IABSD.fr/src/usr.bin/ssh/channels.c

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• Author : djm
  Date : 2026-06-01 05:40:13
  Hash : f1855846
  Message : Actually set pollfd.events correctly for socket type channels; previously we were throwing away the events we computed if the channel had a c->sock distinct from it's other read and write fds. Fortunately, it appears that this case happens rarely, if ever. Reported by Darafei Praliaskouski via GHPR660

• usr.bin/ssh/channels.c

• /* $OpenBSD: channels.c,v 1.461 2026/06/01 05:40:13 djm Exp $ */
  /*
   * Author: Tatu Ylonen <ylo@cs.hut.fi>
   * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   *                    All rights reserved
   * This file contains functions for generic socket connection forwarding.
   * There is also code for initiating connection forwarding for X11 connections,
   * arbitrary tcp/ip connections, and the authentication agent connection.
   *
   * As far as I am concerned, the code I have written for this software
   * can be used freely for any purpose.  Any derived versions of this
   * software must be clearly marked as such, and if the derived work is
   * incompatible with the protocol description in the RFC file, it must be
   * called by a name other than "ssh" or "Secure Shell".
   *
   * SSH2 support added by Markus Friedl.
   * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
   * Copyright (c) 1999 Dug Song.  All rights reserved.
   * Copyright (c) 1999 Theo de Raadt.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/ioctl.h>
  #include <sys/un.h>
  #include <sys/socket.h>
  #include <sys/queue.h>
  
  #include <netinet/in.h>
  #include <arpa/inet.h>
  
  #include <errno.h>
  #include <fcntl.h>
  #include <limits.h>
  #include <netdb.h>
  #include <poll.h>
  #include <stdarg.h>
  #include <stdint.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <termios.h>
  #include <unistd.h>
  
  #include "xmalloc.h"
  #include "ssh.h"
  #include "ssh2.h"
  #include "ssherr.h"
  #include "sshbuf.h"
  #include "packet.h"
  #include "log.h"
  #include "misc.h"
  #include "channels.h"
  #include "compat.h"
  #include "canohost.h"
  #include "pathnames.h"
  #include "match.h"
  
  /* XXX remove once we're satisfied there's no lurking bugs */
  /* #define DEBUG_CHANNEL_POLL 1 */
  
  /* -- agent forwarding */
  #define	NUM_SOCKS	10
  
  /* -- X11 forwarding */
  /* X11 port for display :0 */
  #define X11_BASE_PORT	6000
  /* Maximum number of fake X11 displays to try. */
  #define MAX_DISPLAYS  1000
  
  /* Per-channel callback for pre/post IO actions */
  typedef void chan_fn(struct ssh *, Channel *c);
  
  /*
   * Data structure for storing which hosts are permitted for forward requests.
   * The local sides of any remote forwards are stored in this array to prevent
   * a corrupt remote server from accessing arbitrary TCP/IP ports on our local
   * network (which might be behind a firewall).
   */
  /* XXX: streamlocal wants a path instead of host:port */
  /*      Overload host_to_connect; we could just make this match Forward */
  /*	XXX - can we use listen_host instead of listen_path? */
  struct permission {
  	char *host_to_connect;		/* Connect to 'host'. */
  	int port_to_connect;		/* Connect to 'port'. */
  	char *listen_host;		/* Remote side should listen address. */
  	char *listen_path;		/* Remote side should listen path. */
  	int listen_port;		/* Remote side should listen port. */
  	Channel *downstream;		/* Downstream mux*/
  };
  
  /*
   * Stores the forwarding permission state for a single direction (local or
   * remote).
   */
  struct permission_set {
  	/*
  	 * List of all local permitted host/port pairs to allow for the
  	 * user.
  	 */
  	u_int num_permitted_user;
  	struct permission *permitted_user;
  
  	/*
  	 * List of all permitted host/port pairs to allow for the admin.
  	 */
  	u_int num_permitted_admin;
  	struct permission *permitted_admin;
  
  	/*
  	 * If this is true, all opens/listens are permitted.  This is the
  	 * case on the server on which we have to trust the client anyway,
  	 * and the user could do anything after logging in.
  	 */
  	int all_permitted;
  };
  
  /* Used to record timeouts per channel type */
  struct ssh_channel_timeout {
  	char *type_pattern;
  	int timeout_secs;
  };
  
  /* Master structure for channels state */
  struct ssh_channels {
  	/*
  	 * Pointer to an array containing all allocated channels.  The array
  	 * is dynamically extended as needed.
  	 */
  	Channel **channels;
  
  	/*
  	 * Size of the channel array.  All slots of the array must always be
  	 * initialized (at least the type field); unused slots set to NULL
  	 */
  	u_int channels_alloc;
  
  	/*
  	 * 'channel_pre*' are called just before IO to add any bits
  	 * relevant to channels in the c->io_want bitmasks.
  	 *
  	 * 'channel_post*': perform any appropriate operations for
  	 * channels which have c->io_ready events pending.
  	 */
  	chan_fn **channel_pre;
  	chan_fn **channel_post;
  
  	/* -- tcp forwarding */
  	struct permission_set local_perms;
  	struct permission_set remote_perms;
  
  	/* -- X11 forwarding */
  
  	/* Saved X11 local (client) display. */
  	char *x11_saved_display;
  
  	/* Saved X11 authentication protocol name. */
  	char *x11_saved_proto;
  
  	/* Saved X11 authentication data.  This is the real data. */
  	char *x11_saved_data;
  	u_int x11_saved_data_len;
  
  	/* Deadline after which all X11 connections are refused */
  	time_t x11_refuse_time;
  
  	/*
  	 * Fake X11 authentication data.  This is what the server will be
  	 * sending us; we should replace any occurrences of this by the
  	 * real data.
  	 */
  	u_char *x11_fake_data;
  	u_int x11_fake_data_len;
  
  	/* AF_UNSPEC or AF_INET or AF_INET6 */
  	int IPv4or6;
  
  	/* Channel timeouts by type */
  	struct ssh_channel_timeout *timeouts;
  	size_t ntimeouts;
  	/* Global timeout for all OPEN channels */
  	int global_deadline;
  	time_t lastused;
  	/* pattern-lists used to classify channels as bulk */
  	char *bulk_classifier_tty, *bulk_classifier_notty;
  	/* Number of active bulk channels (set by channel_handler) */
  	u_int nbulk;
  };
  
  /* helper */
  static void port_open_helper(struct ssh *ssh, Channel *c, char *rtype);
  static const char *channel_rfwd_bind_host(const char *listen_host);
  
  /* non-blocking connect helpers */
  static int connect_next(struct channel_connect *);
  static void channel_connect_ctx_free(struct channel_connect *);
  static Channel *rdynamic_connect_prepare(struct ssh *, char *, char *);
  static int rdynamic_connect_finish(struct ssh *, Channel *);
  
  /* Setup helper */
  static void channel_handler_init(struct ssh_channels *sc);
  
  /* -- channel core */
  
  void
  channel_init_channels(struct ssh *ssh)
  {
  	struct ssh_channels *sc;
  
  	if ((sc = calloc(1, sizeof(*sc))) == NULL)
  		fatal_f("allocation failed");
  	sc->channels_alloc = 10;
  	sc->channels = xcalloc(sc->channels_alloc, sizeof(*sc->channels));
  	sc->IPv4or6 = AF_UNSPEC;
  	sc->bulk_classifier_tty = xstrdup(CHANNEL_BULK_TTY);
  	sc->bulk_classifier_notty = xstrdup(CHANNEL_BULK_NOTTY);
  	channel_handler_init(sc);
  
  	ssh->chanctxt = sc;
  }
  
  Channel *
  channel_by_id(struct ssh *ssh, int id)
  {
  	Channel *c;
  
  	if (id < 0 || (u_int)id >= ssh->chanctxt->channels_alloc) {
  		logit_f("%d: bad id", id);
  		return NULL;
  	}
  	c = ssh->chanctxt->channels[id];
  	if (c == NULL) {
  		logit_f("%d: bad id: channel free", id);
  		return NULL;
  	}
  	return c;
  }
  
  Channel *
  channel_by_remote_id(struct ssh *ssh, u_int remote_id)
  {
  	Channel *c;
  	u_int i;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c != NULL && c->have_remote_id && c->remote_id == remote_id)
  			return c;
  	}
  	return NULL;
  }
  
  /*
   * Returns the channel if it is allowed to receive protocol messages.
   * Private channels, like listening sockets, may not receive messages.
   */
  Channel *
  channel_lookup(struct ssh *ssh, int id)
  {
  	Channel *c;
  
  	if ((c = channel_by_id(ssh, id)) == NULL)
  		return NULL;
  
  	switch (c->type) {
  	case SSH_CHANNEL_X11_OPEN:
  	case SSH_CHANNEL_LARVAL:
  	case SSH_CHANNEL_CONNECTING:
  	case SSH_CHANNEL_DYNAMIC:
  	case SSH_CHANNEL_RDYNAMIC_OPEN:
  	case SSH_CHANNEL_RDYNAMIC_FINISH:
  	case SSH_CHANNEL_OPENING:
  	case SSH_CHANNEL_OPEN:
  	case SSH_CHANNEL_ABANDONED:
  	case SSH_CHANNEL_MUX_PROXY:
  		return c;
  	}
  	logit("Non-public channel %d, type %d.", id, c->type);
  	return NULL;
  }
  
  /*
   * Add a timeout for open channels whose c->ctype (or c->xctype if it is set)
   * match type_pattern.
   */
  void
  channel_add_timeout(struct ssh *ssh, const char *type_pattern,
      int timeout_secs)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  
  	if (strcmp(type_pattern, "global") == 0) {
  		debug2_f("global channel timeout %d seconds", timeout_secs);
  		sc->global_deadline = timeout_secs;
  		return;
  	}
  	debug2_f("channel type \"%s\" timeout %d seconds",
  	    type_pattern, timeout_secs);
  	sc->timeouts = xrecallocarray(sc->timeouts, sc->ntimeouts,
  	    sc->ntimeouts + 1, sizeof(*sc->timeouts));
  	sc->timeouts[sc->ntimeouts].type_pattern = xstrdup(type_pattern);
  	sc->timeouts[sc->ntimeouts].timeout_secs = timeout_secs;
  	sc->ntimeouts++;
  }
  
  /* Clears all previously-added channel timeouts */
  void
  channel_clear_timeouts(struct ssh *ssh)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	size_t i;
  
  	debug3_f("clearing");
  	for (i = 0; i < sc->ntimeouts; i++)
  		free(sc->timeouts[i].type_pattern);
  	free(sc->timeouts);
  	sc->timeouts = NULL;
  	sc->ntimeouts = 0;
  }
  
  static int
  lookup_timeout(struct ssh *ssh, const char *type)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	size_t i;
  
  	for (i = 0; i < sc->ntimeouts; i++) {
  		if (match_pattern(type, sc->timeouts[i].type_pattern))
  			return sc->timeouts[i].timeout_secs;
  	}
  
  	return 0;
  }
  
  static void
  channel_classify(struct ssh *ssh, Channel *c)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	const char *type = c->xctype == NULL ? c->ctype : c->xctype;
  	const char *classifier = (c->isatty || c->remote_has_tty) ?
  	    sc->bulk_classifier_tty : sc->bulk_classifier_notty;
  
  	c->bulk = type != NULL && match_pattern_list(type, classifier, 0) == 1;
  }
  
  /*
   * Sets "extended type" of a channel; used by session layer to add additional
   * information about channel types (e.g. shell, login, subsystem) that can then
   * be used to select timeouts and DSCP values.
   * Will reset c->inactive_deadline as a side-effect.
   */
  void
  channel_set_xtype(struct ssh *ssh, int id, const char *xctype)
  {
  	Channel *c;
  
  	if ((c = channel_by_id(ssh, id)) == NULL)
  		fatal_f("missing channel %d", id);
  	if (c->xctype != NULL)
  		free(c->xctype);
  	c->xctype = xstrdup(xctype);
  	/* Type has changed, so look up inactivity deadline again */
  	c->inactive_deadline = lookup_timeout(ssh, c->xctype);
  	channel_classify(ssh, c);
  	debug2_f("labeled channel %d as %s (inactive timeout %u)", id, xctype,
  	    c->inactive_deadline);
  }
  
  /*
   * update "last used" time on a channel.
   * NB. nothing else should update lastused except to clear it.
   */
  static void
  channel_set_used_time(struct ssh *ssh, Channel *c)
  {
  	ssh->chanctxt->lastused = monotime();
  	if (c != NULL)
  		c->lastused = ssh->chanctxt->lastused;
  }
  
  /*
   * Get the time at which a channel is due to time out for inactivity.
   * Returns 0 if the channel is not due to time out ever.
   */
  static time_t
  channel_get_expiry(struct ssh *ssh, Channel *c)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	time_t expiry = 0, channel_expiry;
  
  	if (sc->lastused != 0 && sc->global_deadline != 0)
  		expiry = sc->lastused + sc->global_deadline;
  	if (c->lastused != 0 && c->inactive_deadline != 0) {
  		channel_expiry = c->lastused + c->inactive_deadline;
  		if (expiry == 0 || channel_expiry < expiry)
  			expiry = channel_expiry;
  	}
  	return expiry;
  }
  
  /* Returns non-zero if there is an open, non-interactive channel */
  int
  channel_has_bulk(struct ssh *ssh)
  {
  	return ssh->chanctxt != NULL && ssh->chanctxt->nbulk != 0;
  }
  
  /*
   * Register filedescriptors for a channel, used when allocating a channel or
   * when the channel consumer/producer is ready, e.g. shell exec'd
   */
  static void
  channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,
      int extusage, int nonblock, int is_tty)
  {
  	int val;
  
  	if (rfd != -1)
  		(void)fcntl(rfd, F_SETFD, FD_CLOEXEC);
  	if (wfd != -1 && wfd != rfd)
  		(void)fcntl(wfd, F_SETFD, FD_CLOEXEC);
  	if (efd != -1 && efd != rfd && efd != wfd)
  		(void)fcntl(efd, F_SETFD, FD_CLOEXEC);
  
  	c->rfd = rfd;
  	c->wfd = wfd;
  	c->sock = (rfd == wfd) ? rfd : -1;
  	c->efd = efd;
  	c->extended_usage = extusage;
  
  	if ((c->isatty = is_tty) != 0)
  		debug2("channel %d: rfd %d isatty", c->self, c->rfd);
  
  	/* enable nonblocking mode */
  	c->restore_block = 0;
  	if (nonblock == CHANNEL_NONBLOCK_STDIO) {
  		/*
  		 * Special handling for stdio file descriptors: do not set
  		 * non-blocking mode if they are TTYs. Otherwise prepare to
  		 * restore their blocking state on exit to avoid interfering
  		 * with other programs that follow.
  		 */
  		if (rfd != -1 && !isatty(rfd) &&
  		    (val = fcntl(rfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
  			c->restore_flags[0] = val;
  			c->restore_block |= CHANNEL_RESTORE_RFD;
  			set_nonblock(rfd);
  		}
  		if (wfd != -1 && !isatty(wfd) &&
  		    (val = fcntl(wfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
  			c->restore_flags[1] = val;
  			c->restore_block |= CHANNEL_RESTORE_WFD;
  			set_nonblock(wfd);
  		}
  		if (efd != -1 && !isatty(efd) &&
  		    (val = fcntl(efd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
  			c->restore_flags[2] = val;
  			c->restore_block |= CHANNEL_RESTORE_EFD;
  			set_nonblock(efd);
  		}
  	} else if (nonblock) {
  		if (rfd != -1)
  			set_nonblock(rfd);
  		if (wfd != -1)
  			set_nonblock(wfd);
  		if (efd != -1)
  			set_nonblock(efd);
  	}
  	/* channel might be entering a larval state, so reset global timeout */
  	channel_set_used_time(ssh, NULL);
  	channel_classify(ssh, c);
  }
  
  /*
   * Allocate a new channel object and set its type and socket.
   */
  Channel *
  channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
      u_int window, u_int maxpack, int extusage, const char *remote_name,
      int nonblock)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	u_int i, found;
  	Channel *c;
  	int r;
  
  	/* Try to find a free slot where to put the new channel. */
  	for (i = 0; i < sc->channels_alloc; i++) {
  		if (sc->channels[i] == NULL) {
  			/* Found a free slot. */
  			found = i;
  			break;
  		}
  	}
  	if (i >= sc->channels_alloc) {
  		/*
  		 * There are no free slots. Take last+1 slot and expand
  		 * the array.
  		 */
  		found = sc->channels_alloc;
  		if (sc->channels_alloc > CHANNELS_MAX_CHANNELS)
  			fatal_f("internal error: channels_alloc %d too big",
  			    sc->channels_alloc);
  		sc->channels = xrecallocarray(sc->channels, sc->channels_alloc,
  		    sc->channels_alloc + 10, sizeof(*sc->channels));
  		sc->channels_alloc += 10;
  		debug2("channel: expanding %d", sc->channels_alloc);
  	}
  	/* Initialize and return new channel. */
  	c = sc->channels[found] = xcalloc(1, sizeof(Channel));
  	if ((c->input = sshbuf_new()) == NULL ||
  	    (c->output = sshbuf_new()) == NULL ||
  	    (c->extended = sshbuf_new()) == NULL)
  		fatal_f("sshbuf_new failed");
  	if ((r = sshbuf_set_max_size(c->input, CHAN_INPUT_MAX)) != 0)
  		fatal_fr(r, "sshbuf_set_max_size");
  	c->ostate = CHAN_OUTPUT_OPEN;
  	c->istate = CHAN_INPUT_OPEN;
  	channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, 0);
  	c->self = found;
  	c->type = type;
  	c->ctype = ctype;
  	c->local_window = window;
  	c->local_window_max = window;
  	c->local_maxpacket = maxpack;
  	c->remote_name = xstrdup(remote_name);
  	c->ctl_chan = -1;
  	c->delayed = 1;		/* prevent call to channel_post handler */
  	c->inactive_deadline = lookup_timeout(ssh, c->ctype);
  	TAILQ_INIT(&c->status_confirms);
  	channel_classify(ssh, c);
  	debug("channel %d: new %s [%s] (inactive timeout: %u)",
  	    found, c->ctype, remote_name, c->inactive_deadline);
  	return c;
  }
  
  void
  channel_set_tty(struct ssh *ssh, Channel *c)
  {
  	c->remote_has_tty = 1;
  	channel_classify(ssh, c);
  }
  
  int
  channel_close_fd(struct ssh *ssh, Channel *c, int *fdp)
  {
  	int ret, fd = *fdp;
  
  	if (fd == -1)
  		return 0;
  
  	/* restore blocking */
  	if (*fdp == c->rfd &&
  	    (c->restore_block & CHANNEL_RESTORE_RFD) != 0)
  		(void)fcntl(*fdp, F_SETFL, c->restore_flags[0]);
  	else if (*fdp == c->wfd &&
  	    (c->restore_block & CHANNEL_RESTORE_WFD) != 0)
  		(void)fcntl(*fdp, F_SETFL, c->restore_flags[1]);
  	else if (*fdp == c->efd &&
  	    (c->restore_block & CHANNEL_RESTORE_EFD) != 0)
  		(void)fcntl(*fdp, F_SETFL, c->restore_flags[2]);
  
  	if (*fdp == c->rfd) {
  		c->io_want &= ~SSH_CHAN_IO_RFD;
  		c->io_ready &= ~SSH_CHAN_IO_RFD;
  		c->rfd = -1;
  		c->pfds[0] = -1;
  	}
  	if (*fdp == c->wfd) {
  		c->io_want &= ~SSH_CHAN_IO_WFD;
  		c->io_ready &= ~SSH_CHAN_IO_WFD;
  		c->wfd = -1;
  		c->pfds[1] = -1;
  	}
  	if (*fdp == c->efd) {
  		c->io_want &= ~SSH_CHAN_IO_EFD;
  		c->io_ready &= ~SSH_CHAN_IO_EFD;
  		c->efd = -1;
  		c->pfds[2] = -1;
  	}
  	if (*fdp == c->sock) {
  		c->io_want &= ~SSH_CHAN_IO_SOCK;
  		c->io_ready &= ~SSH_CHAN_IO_SOCK;
  		c->sock = -1;
  		c->pfds[3] = -1;
  	}
  
  	ret = close(fd);
  	*fdp = -1; /* probably redundant */
  	return ret;
  }
  
  /* Close all channel fd/socket. */
  static void
  channel_close_fds(struct ssh *ssh, Channel *c)
  {
  	int sock = c->sock, rfd = c->rfd, wfd = c->wfd, efd = c->efd;
  
  	channel_close_fd(ssh, c, &c->sock);
  	if (rfd != sock)
  		channel_close_fd(ssh, c, &c->rfd);
  	if (wfd != sock && wfd != rfd)
  		channel_close_fd(ssh, c, &c->wfd);
  	if (efd != sock && efd != rfd && efd != wfd)
  		channel_close_fd(ssh, c, &c->efd);
  }
  
  static void
  fwd_perm_clear(struct permission *perm)
  {
  	free(perm->host_to_connect);
  	free(perm->listen_host);
  	free(perm->listen_path);
  	memset(perm, 0, sizeof(*perm));
  }
  
  /* Returns an printable name for the specified forwarding permission list */
  static const char *
  fwd_ident(int who, int where)
  {
  	if (who == FORWARD_ADM) {
  		if (where == FORWARD_LOCAL)
  			return "admin local";
  		else if (where == FORWARD_REMOTE)
  			return "admin remote";
  	} else if (who == FORWARD_USER) {
  		if (where == FORWARD_LOCAL)
  			return "user local";
  		else if (where == FORWARD_REMOTE)
  			return "user remote";
  	}
  	fatal("Unknown forward permission list %d/%d", who, where);
  }
  
  /* Returns the forwarding permission list for the specified direction */
  static struct permission_set *
  permission_set_get(struct ssh *ssh, int where)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  
  	switch (where) {
  	case FORWARD_LOCAL:
  		return &sc->local_perms;
  		break;
  	case FORWARD_REMOTE:
  		return &sc->remote_perms;
  		break;
  	default:
  		fatal_f("invalid forwarding direction %d", where);
  	}
  }
  
  /* Returns pointers to the specified forwarding list and its element count */
  static void
  permission_set_get_array(struct ssh *ssh, int who, int where,
      struct permission ***permpp, u_int **npermpp)
  {
  	struct permission_set *pset = permission_set_get(ssh, where);
  
  	switch (who) {
  	case FORWARD_USER:
  		*permpp = &pset->permitted_user;
  		*npermpp = &pset->num_permitted_user;
  		break;
  	case FORWARD_ADM:
  		*permpp = &pset->permitted_admin;
  		*npermpp = &pset->num_permitted_admin;
  		break;
  	default:
  		fatal_f("invalid forwarding client %d", who);
  	}
  }
  
  /* Adds an entry to the specified forwarding list */
  static int
  permission_set_add(struct ssh *ssh, int who, int where,
      const char *host_to_connect, int port_to_connect,
      const char *listen_host, const char *listen_path, int listen_port,
      Channel *downstream)
  {
  	struct permission **permp;
  	u_int n, *npermp;
  
  	permission_set_get_array(ssh, who, where, &permp, &npermp);
  
  	if (*npermp >= INT_MAX)
  		fatal_f("%s overflow", fwd_ident(who, where));
  
  	*permp = xrecallocarray(*permp, *npermp, *npermp + 1, sizeof(**permp));
  	n = (*npermp)++;
  #define MAYBE_DUP(s) ((s == NULL) ? NULL : xstrdup(s))
  	(*permp)[n].host_to_connect = MAYBE_DUP(host_to_connect);
  	(*permp)[n].port_to_connect = port_to_connect;
  	(*permp)[n].listen_host = MAYBE_DUP(listen_host);
  	(*permp)[n].listen_path = MAYBE_DUP(listen_path);
  	(*permp)[n].listen_port = listen_port;
  	(*permp)[n].downstream = downstream;
  #undef MAYBE_DUP
  	return (int)n;
  }
  
  static void
  mux_remove_remote_forwardings(struct ssh *ssh, Channel *c)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	struct permission *perm;
  	int r;
  	u_int i;
  
  	for (i = 0; i < pset->num_permitted_user; i++) {
  		perm = &pset->permitted_user[i];
  		if (perm->downstream != c)
  			continue;
  
  		/* cancel on the server, since mux client is gone */
  		debug("channel %d: cleanup remote forward for %s:%u",
  		    c->self, perm->listen_host, perm->listen_port);
  		if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
  		    (r = sshpkt_put_cstring(ssh,
  		    "cancel-tcpip-forward")) != 0 ||
  		    (r = sshpkt_put_u8(ssh, 0)) != 0 ||
  		    (r = sshpkt_put_cstring(ssh,
  		    channel_rfwd_bind_host(perm->listen_host))) != 0 ||
  		    (r = sshpkt_put_u32(ssh, perm->listen_port)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0) {
  			fatal_fr(r, "channel %i", c->self);
  		}
  		fwd_perm_clear(perm); /* unregister */
  	}
  }
  
  /* Free the channel and close its fd/socket. */
  void
  channel_free(struct ssh *ssh, Channel *c)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	char *s;
  	u_int i, n;
  	Channel *other;
  	struct channel_confirm *cc;
  
  	for (n = 0, i = 0; i < sc->channels_alloc; i++) {
  		if ((other = sc->channels[i]) == NULL)
  			continue;
  		n++;
  		/* detach from mux client and prepare for closing */
  		if (c->type == SSH_CHANNEL_MUX_CLIENT &&
  		    other->type == SSH_CHANNEL_MUX_PROXY &&
  		    other->mux_ctx == c) {
  			other->mux_ctx = NULL;
  			other->type = SSH_CHANNEL_OPEN;
  			other->istate = CHAN_INPUT_CLOSED;
  			other->ostate = CHAN_OUTPUT_CLOSED;
  		}
  	}
  	debug("channel %d: free: %s, nchannels %u", c->self,
  	    c->remote_name ? c->remote_name : "???", n);
  
  	if (c->type == SSH_CHANNEL_MUX_CLIENT) {
  		mux_remove_remote_forwardings(ssh, c);
  		free(c->mux_ctx);
  		c->mux_ctx = NULL;
  	} else if (c->type == SSH_CHANNEL_MUX_LISTENER) {
  		free(c->mux_ctx);
  		c->mux_ctx = NULL;
  	}
  
  	if (log_level_get() >= SYSLOG_LEVEL_DEBUG3) {
  		s = channel_open_message(ssh);
  		debug3("channel %d: status: %s", c->self, s);
  		free(s);
  	}
  
  	channel_close_fds(ssh, c);
  	sshbuf_free(c->input);
  	sshbuf_free(c->output);
  	sshbuf_free(c->extended);
  	c->input = c->output = c->extended = NULL;
  	free(c->remote_name);
  	c->remote_name = NULL;
  	free(c->path);
  	c->path = NULL;
  	free(c->listening_addr);
  	c->listening_addr = NULL;
  	free(c->xctype);
  	c->xctype = NULL;
  	while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
  		if (cc->abandon_cb != NULL)
  			cc->abandon_cb(ssh, c, cc->ctx);
  		TAILQ_REMOVE(&c->status_confirms, cc, entry);
  		freezero(cc, sizeof(*cc));
  	}
  	if (c->filter_cleanup != NULL && c->filter_ctx != NULL)
  		c->filter_cleanup(ssh, c->self, c->filter_ctx);
  	sc->channels[c->self] = NULL;
  	freezero(c, sizeof(*c));
  }
  
  void
  channel_free_all(struct ssh *ssh)
  {
  	u_int i;
  	struct ssh_channels *sc = ssh->chanctxt;
  
  	for (i = 0; i < sc->channels_alloc; i++)
  		if (sc->channels[i] != NULL)
  			channel_free(ssh, sc->channels[i]);
  
  	free(sc->channels);
  	sc->channels = NULL;
  	sc->channels_alloc = 0;
  
  	free(sc->x11_saved_display);
  	sc->x11_saved_display = NULL;
  
  	free(sc->x11_saved_proto);
  	sc->x11_saved_proto = NULL;
  
  	free(sc->x11_saved_data);
  	sc->x11_saved_data = NULL;
  	sc->x11_saved_data_len = 0;
  
  	free(sc->x11_fake_data);
  	sc->x11_fake_data = NULL;
  	sc->x11_fake_data_len = 0;
  }
  
  void
  channel_free_channels(struct ssh *ssh)
  {
  	struct ssh_channels *sc;
  
  	if (ssh == NULL || ssh->chanctxt == NULL)
  		return;
  	channel_free_all(ssh);
  	channel_clear_permission(ssh, FORWARD_USER, FORWARD_LOCAL);
  	channel_clear_permission(ssh, FORWARD_USER, FORWARD_REMOTE);
  	channel_clear_permission(ssh, FORWARD_ADM, FORWARD_LOCAL);
  	channel_clear_permission(ssh, FORWARD_ADM, FORWARD_REMOTE);
  	sc = ssh->chanctxt;
  	free(sc->bulk_classifier_tty);
  	free(sc->bulk_classifier_notty);
  	free(sc->channel_pre);
  	free(sc->channel_post);
  	freezero(sc, sizeof(*sc));
  	ssh->chanctxt = NULL;
  }
  
  /*
   * Closes the sockets/fds of all channels.  This is used to close extra file
   * descriptors after a fork.
   */
  void
  channel_close_all(struct ssh *ssh)
  {
  	u_int i;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++)
  		if (ssh->chanctxt->channels[i] != NULL)
  			channel_close_fds(ssh, ssh->chanctxt->channels[i]);
  }
  
  /*
   * Stop listening to channels.
   */
  void
  channel_stop_listening(struct ssh *ssh)
  {
  	u_int i;
  	Channel *c;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c != NULL) {
  			switch (c->type) {
  			case SSH_CHANNEL_AUTH_SOCKET:
  			case SSH_CHANNEL_PORT_LISTENER:
  			case SSH_CHANNEL_RPORT_LISTENER:
  			case SSH_CHANNEL_X11_LISTENER:
  			case SSH_CHANNEL_UNIX_LISTENER:
  			case SSH_CHANNEL_RUNIX_LISTENER:
  				channel_close_fd(ssh, c, &c->sock);
  				channel_free(ssh, c);
  				break;
  			}
  		}
  	}
  }
  
  /*
   * Returns true if no channel has too much buffered data, and false if one or
   * more channel is overfull.
   */
  int
  channel_not_very_much_buffered_data(struct ssh *ssh)
  {
  	u_int i;
  	u_int maxsize = ssh_packet_get_maxsize(ssh);
  	Channel *c;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_OPEN)
  			continue;
  		if (sshbuf_len(c->output) > maxsize) {
  			debug2("channel %d: big output buffer %zu > %u",
  			    c->self, sshbuf_len(c->output), maxsize);
  			return 0;
  		}
  	}
  	return 1;
  }
  
  /* Returns true if any channel is still open. */
  int
  channel_still_open(struct ssh *ssh)
  {
  	u_int i;
  	Channel *c;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL)
  			continue;
  		switch (c->type) {
  		case SSH_CHANNEL_X11_LISTENER:
  		case SSH_CHANNEL_PORT_LISTENER:
  		case SSH_CHANNEL_RPORT_LISTENER:
  		case SSH_CHANNEL_MUX_LISTENER:
  		case SSH_CHANNEL_CLOSED:
  		case SSH_CHANNEL_AUTH_SOCKET:
  		case SSH_CHANNEL_DYNAMIC:
  		case SSH_CHANNEL_RDYNAMIC_OPEN:
  		case SSH_CHANNEL_CONNECTING:
  		case SSH_CHANNEL_ZOMBIE:
  		case SSH_CHANNEL_ABANDONED:
  		case SSH_CHANNEL_UNIX_LISTENER:
  		case SSH_CHANNEL_RUNIX_LISTENER:
  			continue;
  		case SSH_CHANNEL_LARVAL:
  			continue;
  		case SSH_CHANNEL_OPENING:
  		case SSH_CHANNEL_OPEN:
  		case SSH_CHANNEL_RDYNAMIC_FINISH:
  		case SSH_CHANNEL_X11_OPEN:
  		case SSH_CHANNEL_MUX_CLIENT:
  		case SSH_CHANNEL_MUX_PROXY:
  			return 1;
  		default:
  			fatal_f("bad channel type %d", c->type);
  			/* NOTREACHED */
  		}
  	}
  	return 0;
  }
  
  /* Returns true if a channel with a TTY is open. */
  int
  channel_tty_open(struct ssh *ssh)
  {
  	u_int i;
  	Channel *c;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_OPEN)
  			continue;
  		if (c->client_tty)
  			return 1;
  	}
  	return 0;
  }
  
  /* Returns the id of an open channel suitable for keepaliving */
  int
  channel_find_open(struct ssh *ssh)
  {
  	u_int i;
  	Channel *c;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL || !c->have_remote_id)
  			continue;
  		switch (c->type) {
  		case SSH_CHANNEL_CLOSED:
  		case SSH_CHANNEL_DYNAMIC:
  		case SSH_CHANNEL_RDYNAMIC_OPEN:
  		case SSH_CHANNEL_RDYNAMIC_FINISH:
  		case SSH_CHANNEL_X11_LISTENER:
  		case SSH_CHANNEL_PORT_LISTENER:
  		case SSH_CHANNEL_RPORT_LISTENER:
  		case SSH_CHANNEL_MUX_LISTENER:
  		case SSH_CHANNEL_MUX_CLIENT:
  		case SSH_CHANNEL_MUX_PROXY:
  		case SSH_CHANNEL_OPENING:
  		case SSH_CHANNEL_CONNECTING:
  		case SSH_CHANNEL_ZOMBIE:
  		case SSH_CHANNEL_ABANDONED:
  		case SSH_CHANNEL_UNIX_LISTENER:
  		case SSH_CHANNEL_RUNIX_LISTENER:
  			continue;
  		case SSH_CHANNEL_LARVAL:
  		case SSH_CHANNEL_AUTH_SOCKET:
  		case SSH_CHANNEL_OPEN:
  		case SSH_CHANNEL_X11_OPEN:
  			return i;
  		default:
  			fatal_f("bad channel type %d", c->type);
  			/* NOTREACHED */
  		}
  	}
  	return -1;
  }
  
  /* Returns the state of the channel's extended usage flag */
  const char *
  channel_format_extended_usage(const Channel *c)
  {
  	if (c->efd == -1)
  		return "closed";
  
  	switch (c->extended_usage) {
  	case CHAN_EXTENDED_WRITE:
  		return "write";
  	case CHAN_EXTENDED_READ:
  		return "read";
  	case CHAN_EXTENDED_IGNORE:
  		return "ignore";
  	default:
  		return "UNKNOWN";
  	}
  }
  
  static char *
  channel_format_status(const Channel *c)
  {
  	char *ret = NULL;
  
  	xasprintf(&ret, "t%d [%s] %s%u %s%u i%u/%zu o%u/%zu e[%s]/%zu "
  	    "fd %d/%d/%d sock %d cc %d %s%u io 0x%02x/0x%02x %s%s",
  	    c->type, c->xctype != NULL ? c->xctype : c->ctype,
  	    c->have_remote_id ? "r" : "nr", c->remote_id,
  	    c->mux_ctx != NULL ? "m" : "nm", c->mux_downstream_id,
  	    c->istate, sshbuf_len(c->input),
  	    c->ostate, sshbuf_len(c->output),
  	    channel_format_extended_usage(c), sshbuf_len(c->extended),
  	    c->rfd, c->wfd, c->efd, c->sock, c->ctl_chan,
  	    c->have_ctl_child_id ? "c" : "nc", c->ctl_child_id,
  	    c->io_want, c->io_ready,
  	    c->isatty ? "T" : (c->remote_has_tty ? "RT" : ""),
  	    c->bulk ? "B" : "I");
  	return ret;
  }
  
  /*
   * Returns a message describing the currently open forwarded connections,
   * suitable for sending to the client.  The message contains crlf pairs for
   * newlines.
   */
  char *
  channel_open_message(struct ssh *ssh)
  {
  	struct sshbuf *buf;
  	Channel *c;
  	u_int i;
  	int r;
  	char *cp, *ret;
  
  	if ((buf = sshbuf_new()) == NULL)
  		fatal_f("sshbuf_new");
  	if ((r = sshbuf_putf(buf,
  	    "The following connections are open:\r\n")) != 0)
  		fatal_fr(r, "sshbuf_putf");
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL)
  			continue;
  		switch (c->type) {
  		case SSH_CHANNEL_X11_LISTENER:
  		case SSH_CHANNEL_PORT_LISTENER:
  		case SSH_CHANNEL_RPORT_LISTENER:
  		case SSH_CHANNEL_CLOSED:
  		case SSH_CHANNEL_AUTH_SOCKET:
  		case SSH_CHANNEL_ZOMBIE:
  		case SSH_CHANNEL_ABANDONED:
  		case SSH_CHANNEL_MUX_LISTENER:
  		case SSH_CHANNEL_UNIX_LISTENER:
  		case SSH_CHANNEL_RUNIX_LISTENER:
  			continue;
  		case SSH_CHANNEL_LARVAL:
  		case SSH_CHANNEL_OPENING:
  		case SSH_CHANNEL_CONNECTING:
  		case SSH_CHANNEL_DYNAMIC:
  		case SSH_CHANNEL_RDYNAMIC_OPEN:
  		case SSH_CHANNEL_RDYNAMIC_FINISH:
  		case SSH_CHANNEL_OPEN:
  		case SSH_CHANNEL_X11_OPEN:
  		case SSH_CHANNEL_MUX_PROXY:
  		case SSH_CHANNEL_MUX_CLIENT:
  			cp = channel_format_status(c);
  			if ((r = sshbuf_putf(buf, "  #%d %.300s (%s)\r\n",
  			    c->self, c->remote_name, cp)) != 0) {
  				free(cp);
  				fatal_fr(r, "sshbuf_putf");
  			}
  			free(cp);
  			continue;
  		default:
  			fatal_f("bad channel type %d", c->type);
  			/* NOTREACHED */
  		}
  	}
  	if ((ret = sshbuf_dup_string(buf)) == NULL)
  		fatal_f("sshbuf_dup_string");
  	sshbuf_free(buf);
  	return ret;
  }
  
  void
  channel_report_open(struct ssh *ssh, int level)
  {
  	char *open, *oopen, *cp, ident[256];
  
  	sshpkt_fmt_connection_id(ssh, ident, sizeof(ident));
  	do_log2(level, "Connection: %s (pid %ld)", ident, (long)getpid());
  	open = oopen = channel_open_message(ssh);
  	while ((cp = strsep(&open, "\r\n")) != NULL) {
  		if (*cp != '\0')
  			do_log2(level, "%s", cp);
  	}
  	free(oopen);
  }
  
  static void
  open_preamble(struct ssh *ssh, const char *where, Channel *c, const char *type)
  {
  	int r;
  
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN)) != 0 ||
  	    (r = sshpkt_put_cstring(ssh, type)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0) {
  		fatal_r(r, "%s: channel %i: open", where, c->self);
  	}
  }
  
  void
  channel_send_open(struct ssh *ssh, int id)
  {
  	Channel *c = channel_lookup(ssh, id);
  	int r;
  
  	if (c == NULL) {
  		logit("channel_send_open: %d: bad id", id);
  		return;
  	}
  	debug2("channel %d: send open", id);
  	open_preamble(ssh, __func__, c, c->ctype);
  	if ((r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i", c->self);
  }
  
  void
  channel_request_start(struct ssh *ssh, int id, const char *service,
      int wantconfirm)
  {
  	Channel *c = channel_lookup(ssh, id);
  	int r;
  
  	if (c == NULL) {
  		logit_f("%d: unknown channel id", id);
  		return;
  	}
  	if (!c->have_remote_id)
  		fatal_f("channel %d: no remote id", c->self);
  
  	debug2("channel %d: request %s confirm %d", id, service, wantconfirm);
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_REQUEST)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  	    (r = sshpkt_put_cstring(ssh, service)) != 0 ||
  	    (r = sshpkt_put_u8(ssh, wantconfirm)) != 0) {
  		fatal_fr(r, "channel %i", c->self);
  	}
  }
  
  void
  channel_register_status_confirm(struct ssh *ssh, int id,
      channel_confirm_cb *cb, channel_confirm_abandon_cb *abandon_cb, void *ctx)
  {
  	struct channel_confirm *cc;
  	Channel *c;
  
  	if ((c = channel_lookup(ssh, id)) == NULL)
  		fatal_f("%d: bad id", id);
  
  	cc = xcalloc(1, sizeof(*cc));
  	cc->cb = cb;
  	cc->abandon_cb = abandon_cb;
  	cc->ctx = ctx;
  	TAILQ_INSERT_TAIL(&c->status_confirms, cc, entry);
  }
  
  void
  channel_register_open_confirm(struct ssh *ssh, int id,
      channel_open_fn *fn, void *ctx)
  {
  	Channel *c = channel_lookup(ssh, id);
  
  	if (c == NULL) {
  		logit_f("%d: bad id", id);
  		return;
  	}
  	c->open_confirm = fn;
  	c->open_confirm_ctx = ctx;
  }
  
  void
  channel_register_cleanup(struct ssh *ssh, int id,
      channel_callback_fn *fn, int do_close)
  {
  	Channel *c = channel_by_id(ssh, id);
  
  	if (c == NULL) {
  		logit_f("%d: bad id", id);
  		return;
  	}
  	c->detach_user = fn;
  	c->detach_close = do_close;
  }
  
  void
  channel_cancel_cleanup(struct ssh *ssh, int id)
  {
  	Channel *c = channel_by_id(ssh, id);
  
  	if (c == NULL) {
  		logit_f("%d: bad id", id);
  		return;
  	}
  	c->detach_user = NULL;
  	c->detach_close = 0;
  }
  
  void
  channel_register_filter(struct ssh *ssh, int id, channel_infilter_fn *ifn,
      channel_outfilter_fn *ofn, channel_filter_cleanup_fn *cfn, void *ctx)
  {
  	Channel *c = channel_lookup(ssh, id);
  
  	if (c == NULL) {
  		logit_f("%d: bad id", id);
  		return;
  	}
  	c->input_filter = ifn;
  	c->output_filter = ofn;
  	c->filter_ctx = ctx;
  	c->filter_cleanup = cfn;
  }
  
  void
  channel_set_fds(struct ssh *ssh, int id, int rfd, int wfd, int efd,
      int extusage, int nonblock, int is_tty, u_int window_max)
  {
  	Channel *c = channel_lookup(ssh, id);
  	int r;
  
  	if (c == NULL || c->type != SSH_CHANNEL_LARVAL)
  		fatal("channel_activate for non-larval channel %d.", id);
  	if (!c->have_remote_id)
  		fatal_f("channel %d: no remote id", c->self);
  
  	channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, is_tty);
  	c->type = SSH_CHANNEL_OPEN;
  	channel_set_used_time(ssh, c);
  	c->local_window = c->local_window_max = window_max;
  
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i", c->self);
  }
  
  static void
  channel_pre_listener(struct ssh *ssh, Channel *c)
  {
  	c->io_want = SSH_CHAN_IO_SOCK_R;
  }
  
  static void
  channel_pre_connecting(struct ssh *ssh, Channel *c)
  {
  	debug3("channel %d: waiting for connection", c->self);
  	c->io_want = SSH_CHAN_IO_SOCK_W;
  }
  
  static void
  channel_pre_open(struct ssh *ssh, Channel *c)
  {
  	c->io_want = 0;
  	if (c->istate == CHAN_INPUT_OPEN &&
  	    c->remote_window > 0 &&
  	    sshbuf_len(c->input) < c->remote_window &&
  	    sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
  		c->io_want |= SSH_CHAN_IO_RFD;
  	if (c->ostate == CHAN_OUTPUT_OPEN ||
  	    c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
  		if (sshbuf_len(c->output) > 0) {
  			c->io_want |= SSH_CHAN_IO_WFD;
  		} else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
  			if (CHANNEL_EFD_OUTPUT_ACTIVE(c))
  				debug2("channel %d: "
  				    "obuf_empty delayed efd %d/(%zu)", c->self,
  				    c->efd, sshbuf_len(c->extended));
  			else
  				chan_obuf_empty(ssh, c);
  		}
  	}
  	/** XXX check close conditions, too */
  	if (c->efd != -1 && !(c->istate == CHAN_INPUT_CLOSED &&
  	    c->ostate == CHAN_OUTPUT_CLOSED)) {
  		if (c->extended_usage == CHAN_EXTENDED_WRITE &&
  		    sshbuf_len(c->extended) > 0)
  			c->io_want |= SSH_CHAN_IO_EFD_W;
  		else if (c->efd != -1 && !(c->flags & CHAN_EOF_SENT) &&
  		    (c->extended_usage == CHAN_EXTENDED_READ ||
  		    c->extended_usage == CHAN_EXTENDED_IGNORE) &&
  		    sshbuf_len(c->extended) < c->remote_window)
  			c->io_want |= SSH_CHAN_IO_EFD_R;
  	}
  	/* XXX: What about efd? races? */
  }
  
  /*
   * This is a special state for X11 authentication spoofing.  An opened X11
   * connection (when authentication spoofing is being done) remains in this
   * state until the first packet has been completely read.  The authentication
   * data in that packet is then substituted by the real data if it matches the
   * fake data, and the channel is put into normal mode.
   * XXX All this happens at the client side.
   * Returns: 0 = need more data, -1 = wrong cookie, 1 = ok
   */
  static int
  x11_open_helper(struct ssh *ssh, struct sshbuf *b)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	u_char *ucp;
  	u_int proto_len, data_len;
  
  	if (sc->x11_saved_proto == NULL) {
  		error("X11 forwarding opened before X11 forwarding requested");
  		return -1;
  	}
  
  	/* Is this being called after the refusal deadline? */
  	if (sc->x11_refuse_time != 0 &&
  	    monotime() >= sc->x11_refuse_time) {
  		verbose("Rejected X11 connection after ForwardX11Timeout "
  		    "expired");
  		return -1;
  	}
  
  	/* Check if the fixed size part of the packet is in buffer. */
  	if (sshbuf_len(b) < 12)
  		return 0;
  
  	/* Parse the lengths of variable-length fields. */
  	ucp = sshbuf_mutable_ptr(b);
  	if (ucp[0] == 0x42) {	/* Byte order MSB first. */
  		proto_len = 256 * ucp[6] + ucp[7];
  		data_len = 256 * ucp[8] + ucp[9];
  	} else if (ucp[0] == 0x6c) {	/* Byte order LSB first. */
  		proto_len = ucp[6] + 256 * ucp[7];
  		data_len = ucp[8] + 256 * ucp[9];
  	} else {
  		debug2("Initial X11 packet contains bad byte order byte: 0x%x",
  		    ucp[0]);
  		return -1;
  	}
  
  	/* Check if the whole packet is in buffer. */
  	if (sshbuf_len(b) <
  	    12 + ((proto_len + 3) & ~3) + ((data_len + 3) & ~3))
  		return 0;
  
  	/* Check if authentication protocol matches. */
  	if (proto_len != strlen(sc->x11_saved_proto) ||
  	    memcmp(ucp + 12, sc->x11_saved_proto, proto_len) != 0) {
  		debug2("X11 connection uses different authentication protocol.");
  		return -1;
  	}
  	/* Check if authentication data matches our fake data. */
  	if (data_len != sc->x11_fake_data_len ||
  	    timingsafe_bcmp(ucp + 12 + ((proto_len + 3) & ~3),
  		sc->x11_fake_data, sc->x11_fake_data_len) != 0) {
  		debug2("X11 auth data does not match fake data.");
  		return -1;
  	}
  	/* Check fake data length */
  	if (sc->x11_fake_data_len != sc->x11_saved_data_len) {
  		error("X11 fake_data_len %d != saved_data_len %d",
  		    sc->x11_fake_data_len, sc->x11_saved_data_len);
  		return -1;
  	}
  	/*
  	 * Received authentication protocol and data match
  	 * our fake data. Substitute the fake data with real
  	 * data.
  	 */
  	memcpy(ucp + 12 + ((proto_len + 3) & ~3),
  	    sc->x11_saved_data, sc->x11_saved_data_len);
  	return 1;
  }
  
  void
  channel_force_close(struct ssh *ssh, Channel *c, int abandon)
  {
  	debug3_f("channel %d: forcibly closing", c->self);
  	if (c->istate == CHAN_INPUT_OPEN)
  		chan_read_failed(ssh, c);
  	if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
  		sshbuf_reset(c->input);
  		chan_ibuf_empty(ssh, c);
  	}
  	if (c->ostate == CHAN_OUTPUT_OPEN ||
  	    c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
  		sshbuf_reset(c->output);
  		chan_write_failed(ssh, c);
  	}
  	if (c->detach_user)
  		c->detach_user(ssh, c->self, 1, NULL);
  	if (c->efd != -1)
  		channel_close_fd(ssh, c, &c->efd);
  	if (abandon)
  		c->type = SSH_CHANNEL_ABANDONED;
  	/* exempt from inactivity timeouts */
  	c->inactive_deadline = 0;
  	c->lastused = 0;
  }
  
  static void
  channel_pre_x11_open(struct ssh *ssh, Channel *c)
  {
  	int ret = x11_open_helper(ssh, c->output);
  
  	/* c->force_drain = 1; */
  
  	if (ret == 1) {
  		c->type = SSH_CHANNEL_OPEN;
  		channel_set_used_time(ssh, c);
  		channel_pre_open(ssh, c);
  	} else if (ret == -1) {
  		logit("X11 connection rejected because of wrong "
  		    "authentication.");
  		debug2("X11 rejected %d i%d/o%d",
  		    c->self, c->istate, c->ostate);
  		channel_force_close(ssh, c, 0);
  	}
  }
  
  static void
  channel_pre_mux_client(struct ssh *ssh, Channel *c)
  {
  	c->io_want = 0;
  	if (c->istate == CHAN_INPUT_OPEN && !c->mux_pause &&
  	    sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
  		c->io_want |= SSH_CHAN_IO_RFD;
  	if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
  		/* clear buffer immediately (discard any partial packet) */
  		sshbuf_reset(c->input);
  		chan_ibuf_empty(ssh, c);
  		/* Start output drain. XXX just kill chan? */
  		chan_rcvd_oclose(ssh, c);
  	}
  	if (c->ostate == CHAN_OUTPUT_OPEN ||
  	    c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
  		if (sshbuf_len(c->output) > 0)
  			c->io_want |= SSH_CHAN_IO_WFD;
  		else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN)
  			chan_obuf_empty(ssh, c);
  	}
  }
  
  static inline int
  socks_decode_error(Channel *c, int status, const char *func, const char *msg)
  {
  	if (status == SSH_ERR_MESSAGE_INCOMPLETE)
  		return 0;
  	else {
  		debug_r(status, "%s: channel %d: decode %s",
  		    func, c->self, msg);
  		return -1;
  	}
  }
  
  /* try to decode a socks4 header */
  static int
  channel_decode_socks4(Channel *c, struct sshbuf *input, struct sshbuf *output)
  {
  	uint8_t socks_ver, socks_cmd, dest_addr[4];
  	uint16_t dest_port;
  	char *user = NULL, *host = NULL;
  	int success = -1, socks4a = 0, r;
  	struct sshbuf *b = NULL;
  
  	if (sshbuf_len(input) < 9)
  		return 0;
  
  	/* We may not have a complete message, so work on a dup of the buffer */
  	if ((b = sshbuf_fromb(input)) == NULL)
  		fatal_f("sshbuf_fromb failed");
  
  	debug2("channel %d: decode socks4", c->self);
  	if ((r = sshbuf_get_u8(b, &socks_ver)) != 0 ||
  	    (r = sshbuf_get_u8(b, &socks_cmd)) != 0 ||
  	    (r = sshbuf_get_u16(b, &dest_port)) != 0 ||
  	    (r = sshbuf_get(b, &dest_addr, sizeof(dest_addr))) != 0 ||
  	    (r = sshbuf_get_nulterminated_string(b, 1024, &user, NULL)) != 0) {
  		success = socks_decode_error(c, r, __func__, "header");
  		goto out;
  	}
  
  	/* Is this a SOCKS4A request? (indicated by an address of 0.0.0.x) */
  	if (dest_addr[0] == 0 && dest_addr[1] == 0 &&
  	    dest_addr[2] == 0 && dest_addr[3] != 0) {
  		/* If so, then the hostname follows, also nul-terminated */
  		if ((r = sshbuf_get_nulterminated_string(b, 1024,
  		    &host, NULL)) != 0) {
  			success = socks_decode_error(c, r, __func__, "host");
  			goto out;
  		}
  		socks4a = 1;
  	} else {
  		/* Plain SOCKS4 passes an IPv4 binary address; reconstruct */
  		xasprintf(&host, "%d.%d.%d.%d",
  		    dest_addr[0], dest_addr[1], dest_addr[2], dest_addr[3]);
  	}
  
  	/* We have a complete SOCKS4 message; consume it from input */
  	if ((r = sshbuf_consume_upto_child(input, b)) != 0)
  		fatal_fr(r, "channel %d: consume", c->self);
  
  	/* Handle the request */
  	debug2("channel %d: %s: user=\"%s\" command=%d destination=[%s]:%d",
  	    c->self, socks4a ? "SOCKS4A" : "SOCKS4", user, (int)socks_cmd,
  	    host, dest_port);
  	if (socks_cmd != 1) {
  		debug("channel %d: cannot handle %s command 0x%02x",
  		    c->self, socks4a ? "SOCKS4A" : "SOCKS4", socks_cmd);
  		goto out;
  	}
  	free(c->path);
  	c->path = host;
  	host = NULL; /* transferred */
  	c->host_port = dest_port;
  
  	/* Reply to the SOCKS4 client */
  	if ((r = sshbuf_put_u8(output, 0)) != 0 ||	/* vn: 0 for reply */
  	    (r = sshbuf_put_u8(output, 90)) != 0 ||	/* cd: req granted */
  	    (r = sshbuf_put_u16(output, 0)) != 0 ||	/* port: ignored */
  	    (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0) /* ignored */
  		fatal_fr(r, "channel %d: compose reply", c->self);
  
  	/* success */
  	success = 1;
   out:
  	sshbuf_free(b);
  	free(user);
  	free(host);
  	return success;
  }
  
  /* try to decode a socks5 header */
  #define SSH_SOCKS5_AUTHDONE	0x1000
  #define SSH_SOCKS5_NOAUTH	0x00
  #define SSH_SOCKS5_IPV4		0x01
  #define SSH_SOCKS5_DOMAIN	0x03
  #define SSH_SOCKS5_IPV6		0x04
  #define SSH_SOCKS5_CONNECT	0x01
  #define SSH_SOCKS5_SUCCESS	0x00
  
  /*
   * Handles SOCKS5 authentication. Note 'b' must be a dup of 'input'
   * Returns 0 on insufficient queued date, 1 on authentication success or
   * -1 on error.
   */
  static int
  channel_socks5_check_auth(Channel *c, struct sshbuf *b, struct sshbuf *input,
      struct sshbuf *output)
  {
  	uint8_t socks_ver;
  	uint8_t nmethods, method;
  	int r;
  	u_int i, found;
  
  	/* format: ver | nmethods | methods */
  	if ((r = sshbuf_get_u8(b, &socks_ver)) != 0)
  		return socks_decode_error(c, r, __func__, "version");
  	if (socks_ver != 5) /* shouldn't happen; checked by caller^2 */
  		fatal_fr(r, "channel %d: internal error: not socks5", c->self);
  	if ((r = sshbuf_get_u8(b, &nmethods)) != 0)
  		return socks_decode_error(c, r, __func__, "methods");
  	for (found = i = 0; i < nmethods; i++) {
  		if ((r = sshbuf_get_u8(b, &method)) != 0)
  			return socks_decode_error(c, r, __func__, "method");
  		if (method == SSH_SOCKS5_NOAUTH)
  			found = 1;
  	}
  	if (!found) {
  		debug("channel %d: didn't request SSH_SOCKS5_NOAUTH", c->self);
  		return -1;
  	}
  	/* Consume completed request */
  	if ((r = sshbuf_consume_upto_child(input, b)) != 0)
  		fatal_fr(r, "channel %d: consume", c->self);
  
  	/* Compose reply: version, method */
  	if ((r = sshbuf_put_u8(output, 0x05)) != 0 ||
  	    (r = sshbuf_put_u8(output, SSH_SOCKS5_NOAUTH)) != 0)
  		fatal_fr(r, "channel %d: append reply", c->self);
  	/* success */
  	debug2("channel %d: socks5 auth done", c->self);
  	return 1;
  }
  
  static int
  channel_decode_socks5(Channel *c, struct sshbuf *input, struct sshbuf *output)
  {
  	uint8_t socks_ver, socks_cmd, socks_reserved, socks_atyp, addrlen;
  	uint16_t dest_port;
  	char dest_addr[255+1], ntop[INET6_ADDRSTRLEN];
  	u_int af;
  	int r, success = -1;;
  	struct sshbuf *b = NULL;
  
  	debug2("channel %d: decode socks5 %s", c->self,
  	    (c->flags & SSH_SOCKS5_AUTHDONE) ? "request" : "auth");
  
  	/* We may not have a complete message, so work on a dup of the buffer */
  	if ((b = sshbuf_fromb(input)) == NULL)
  		fatal_f("sshbuf_fromb failed");
  
  	if (!(c->flags & SSH_SOCKS5_AUTHDONE)) {
  		if ((r = channel_socks5_check_auth(c, b, input, output)) != 1) {
  			success = r;
  			goto out;
  		}
  		c->flags |= SSH_SOCKS5_AUTHDONE;
  		/* Continue to parse request in case client speculated ahead */
  	}
  
  	/* Request messages (auth or connect) always start with the version */
  	if ((r = sshbuf_get_u8(b, &socks_ver)) != 0) {
  		success = socks_decode_error(c, r, __func__, "version");
  		goto out;
  	}
  	if (socks_ver != 5) /* shouldn't happen */
  		fatal_fr(r, "channel %d: internal error: not socks5", c->self);
  
  	/* Parse SOCKS5 request header */
  	debug2("channel %d: socks5 post auth", c->self);
  	if ((r = sshbuf_get_u8(b, &socks_cmd)) != 0 ||
  	    (r = sshbuf_get_u8(b, &socks_reserved)) != 0 ||
  	    (r = sshbuf_get_u8(b, &socks_atyp)) != 0) {
  		success = socks_decode_error(c, r, __func__, "request header");
  		goto out;
  	}
  
  	if (socks_ver != 0x05 ||
  	    socks_cmd != SSH_SOCKS5_CONNECT ||
  	    socks_reserved != 0x00) {
  		debug2("channel %d: only socks5 connect supported", c->self);
  		goto out;
  	}
  
  	switch (socks_atyp) {
  	case SSH_SOCKS5_IPV4:
  		addrlen = 4;
  		af = AF_INET;
  		break;
  	case SSH_SOCKS5_DOMAIN:
  		if ((r = sshbuf_get_u8(b, &addrlen)) != 0) {
  			success = socks_decode_error(c, r, __func__, "addrlen");
  			goto out;
  		}
  		af = -1;
  		break;
  	case SSH_SOCKS5_IPV6:
  		addrlen = 16;
  		af = AF_INET6;
  		break;
  	default:
  		debug2("channel %d: bad socks5 atyp %d", c->self, socks_atyp);
  		goto out;
  	}
  	if ((r = sshbuf_get(b, &dest_addr, addrlen)) != 0 ||
  	    (r = sshbuf_get_u16(b, &dest_port)) != 0) {
  		success = socks_decode_error(c, r, __func__, "addr/port");
  		goto out;
  	}
  	dest_addr[addrlen] = '\0';
  
  	/* We have a complete SOCKS5 request; consume it from input */
  	if ((r = sshbuf_consume_upto_child(input, b)) != 0)
  		fatal_fr(r, "channel %d: consume", c->self);
  
  	free(c->path);
  	c->path = NULL;
  	if (socks_atyp == SSH_SOCKS5_DOMAIN)
  		c->path = xstrdup(dest_addr);
  	else {
  		if (inet_ntop(af, dest_addr, ntop, sizeof(ntop)) == NULL)
  			return -1;
  		c->path = xstrdup(ntop);
  	}
  	c->host_port = dest_port;
  
  	debug2("channel %d: dynamic request: socks5 host %s port %u command %u",
  	    c->self, c->path, c->host_port, socks_cmd);
  
  	/* Reply */
  	if ((r = sshbuf_put_u8(output, 0x05)) != 0 ||	/* version */
  	    (r = sshbuf_put_u8(output, SSH_SOCKS5_SUCCESS)) != 0 || /* cmd */
  	    (r = sshbuf_put_u8(output, 0)) != 0 ||	/* reserved, ignored */
  	    (r = sshbuf_put_u8(output, SSH_SOCKS5_IPV4)) != 0 || /* addrtype */
  	    (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0 || /* addr */
  	    (r = sshbuf_put_u16(output, dest_port)) != 0) /* port */
  		fatal_fr(r, "channel %d: append reply", c->self);
  
  	/* success */
  	success = 1;
   out:
  	sshbuf_free(b);
  	return success;
  }
  
  Channel *
  channel_connect_stdio_fwd(struct ssh *ssh,
      const char *host_to_connect, int port_to_connect,
      int in, int out, int nonblock)
  {
  	Channel *c;
  
  	debug_f("%s:%d", host_to_connect, port_to_connect);
  
  	c = channel_new(ssh, "stdio-forward", SSH_CHANNEL_OPENING, in, out,
  	    -1, CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
  	    0, "stdio-forward", nonblock);
  
  	c->path = xstrdup(host_to_connect);
  	c->host_port = port_to_connect;
  	c->listening_port = 0;
  	c->force_drain = 1;
  
  	channel_register_fds(ssh, c, in, out, -1, 0, 1, 0);
  	port_open_helper(ssh, c, port_to_connect == PORT_STREAMLOCAL ?
  	    "direct-streamlocal@openssh.com" : "direct-tcpip");
  
  	return c;
  }
  
  /* dynamic port forwarding */
  static void
  channel_pre_dynamic(struct ssh *ssh, Channel *c)
  {
  	u_int have;
  	u_char ver;
  	int r, ret;
  
  	c->io_want = 0;
  	have = sshbuf_len(c->input);
  	debug2("channel %d: pre_dynamic: have %d", c->self, have);
  	/* sshbuf_dump(c->input, stderr); */
  	/* check if the fixed size part of the packet is in buffer. */
  	if (have < 3) {
  		/* need more */
  		c->io_want |= SSH_CHAN_IO_RFD;
  		return;
  	}
  	/* try to guess the protocol */
  	if ((r = sshbuf_peek_u8(c->input, 0, &ver)) != 0)
  		fatal_fr(r, "sshbuf_peek_u8");
  	switch (ver) {
  	case 0x04:
  		ret = channel_decode_socks4(c, c->input, c->output);
  		break;
  	case 0x05:
  		ret = channel_decode_socks5(c, c->input, c->output);
  		break;
  	default:
  		debug2_f("channel %d: unknown SOCKS version %u", c->self, ver);
  		ret = -1;
  		break;
  	}
  	if (ret < 0) {
  		chan_mark_dead(ssh, c);
  	} else if (ret == 0) {
  		debug2("channel %d: pre_dynamic: need more", c->self);
  		/* need more */
  		c->io_want |= SSH_CHAN_IO_RFD;
  		if (sshbuf_len(c->output))
  			c->io_want |= SSH_CHAN_IO_WFD;
  	} else {
  		/* switch to the next state */
  		c->type = SSH_CHANNEL_OPENING;
  		port_open_helper(ssh, c, "direct-tcpip");
  	}
  }
  
  /* simulate read-error */
  static void
  rdynamic_close(struct ssh *ssh, Channel *c)
  {
  	c->type = SSH_CHANNEL_OPEN;
  	channel_force_close(ssh, c, 0);
  }
  
  /* reverse dynamic port forwarding */
  static void
  channel_before_prepare_io_rdynamic(struct ssh *ssh, Channel *c)
  {
  	const u_char *p;
  	u_int have, len;
  	int r, ret;
  
  	have = sshbuf_len(c->output);
  	debug2("channel %d: pre_rdynamic: have %d", c->self, have);
  	/* sshbuf_dump(c->output, stderr); */
  	/* EOF received */
  	if (c->flags & CHAN_EOF_RCVD) {
  		if ((r = sshbuf_consume(c->output, have)) != 0)
  			fatal_fr(r, "channel %d: consume", c->self);
  		rdynamic_close(ssh, c);
  		return;
  	}
  	/* check if the fixed size part of the packet is in buffer. */
  	if (have < 3)
  		return;
  	/* try to guess the protocol */
  	p = sshbuf_ptr(c->output);
  	switch (p[0]) {
  	case 0x04:
  		/* switch input/output for reverse forwarding */
  		ret = channel_decode_socks4(c, c->output, c->input);
  		break;
  	case 0x05:
  		ret = channel_decode_socks5(c, c->output, c->input);
  		break;
  	default:
  		ret = -1;
  		break;
  	}
  	if (ret < 0) {
  		rdynamic_close(ssh, c);
  	} else if (ret == 0) {
  		debug2("channel %d: pre_rdynamic: need more", c->self);
  		/* send socks request to peer */
  		len = sshbuf_len(c->input);
  		if (len > 0 && len < c->remote_window) {
  			if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  			    (r = sshpkt_put_stringb(ssh, c->input)) != 0 ||
  			    (r = sshpkt_send(ssh)) != 0) {
  				fatal_fr(r, "channel %i: rdynamic", c->self);
  			}
  			if ((r = sshbuf_consume(c->input, len)) != 0)
  				fatal_fr(r, "channel %d: consume", c->self);
  			c->remote_window -= len;
  		}
  	} else if (rdynamic_connect_finish(ssh, c) < 0) {
  		/* the connect failed */
  		rdynamic_close(ssh, c);
  	}
  }
  
  /* This is our fake X11 server socket. */
  static void
  channel_post_x11_listener(struct ssh *ssh, Channel *c)
  {
  	Channel *nc;
  	struct sockaddr_storage addr;
  	int r, newsock, oerrno, remote_port;
  	socklen_t addrlen;
  	char buf[16384], *remote_ipaddr;
  
  	if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
  		return;
  
  	debug("X11 connection requested.");
  	addrlen = sizeof(addr);
  	newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  	if (c->single_connection) {
  		oerrno = errno;
  		debug2("single_connection: closing X11 listener.");
  		channel_close_fd(ssh, c, &c->sock);
  		chan_mark_dead(ssh, c);
  		errno = oerrno;
  	}
  	if (newsock == -1) {
  		if (errno != EINTR && errno != EWOULDBLOCK &&
  		    errno != ECONNABORTED)
  			error("accept: %.100s", strerror(errno));
  		if (errno == EMFILE || errno == ENFILE)
  			c->notbefore = monotime() + 1;
  		return;
  	}
  	set_nodelay(newsock);
  	remote_ipaddr = get_peer_ipaddr(newsock);
  	remote_port = get_peer_port(newsock);
  	snprintf(buf, sizeof buf, "X11 connection from %.200s port %d",
  	    remote_ipaddr, remote_port);
  
  	nc = channel_new(ssh, "x11-connection",
  	    SSH_CHANNEL_OPENING, newsock, newsock, -1,
  	    c->local_window_max, c->local_maxpacket, 0, buf, 1);
  	open_preamble(ssh, __func__, nc, "x11");
  	if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, remote_port)) != 0) {
  		fatal_fr(r, "channel %i: reply", c->self);
  	}
  	if ((r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i: send", c->self);
  	free(remote_ipaddr);
  }
  
  static void
  port_open_helper(struct ssh *ssh, Channel *c, char *rtype)
  {
  	char *local_ipaddr = get_local_ipaddr(c->sock);
  	int local_port = c->sock == -1 ? 65536 : get_local_port(c->sock);
  	char *remote_ipaddr = get_peer_ipaddr(c->sock);
  	int remote_port = get_peer_port(c->sock);
  	int r;
  
  	if (remote_port == -1) {
  		/* Fake addr/port to appease peers that validate it (Tectia) */
  		free(remote_ipaddr);
  		remote_ipaddr = xstrdup("127.0.0.1");
  		remote_port = 65535;
  	}
  
  	free(c->remote_name);
  	xasprintf(&c->remote_name,
  	    "%s: listening port %d for %.100s port %d, "
  	    "connect from %.200s port %d to %.100s port %d",
  	    rtype, c->listening_port, c->path, c->host_port,
  	    remote_ipaddr, remote_port, local_ipaddr, local_port);
  
  	open_preamble(ssh, __func__, c, rtype);
  	if (strcmp(rtype, "direct-tcpip") == 0) {
  		/* target host, port */
  		if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, c->host_port)) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	} else if (strcmp(rtype, "direct-streamlocal@openssh.com") == 0) {
  		/* target path */
  		if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	} else if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
  		/* listen path */
  		if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	} else {
  		/* listen address, port */
  		if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, local_port)) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	}
  	if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
  		/* reserved for future owner/mode info */
  		if ((r = sshpkt_put_cstring(ssh, "")) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	} else {
  		/* originator host and port */
  		if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, (u_int)remote_port)) != 0)
  			fatal_fr(r, "channel %i: reply", c->self);
  	}
  	if ((r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i: send", c->self);
  	free(remote_ipaddr);
  	free(local_ipaddr);
  }
  
  void
  channel_set_x11_refuse_time(struct ssh *ssh, time_t refuse_time)
  {
  	ssh->chanctxt->x11_refuse_time = refuse_time;
  }
  
  /*
   * This socket is listening for connections to a forwarded TCP/IP port.
   */
  static void
  channel_post_port_listener(struct ssh *ssh, Channel *c)
  {
  	Channel *nc;
  	struct sockaddr_storage addr;
  	int newsock, nextstate;
  	socklen_t addrlen;
  	char *rtype;
  
  	if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
  		return;
  
  	debug("Connection to port %d forwarding to %.100s port %d requested.",
  	    c->listening_port, c->path, c->host_port);
  
  	if (c->type == SSH_CHANNEL_RPORT_LISTENER) {
  		nextstate = SSH_CHANNEL_OPENING;
  		rtype = "forwarded-tcpip";
  	} else if (c->type == SSH_CHANNEL_RUNIX_LISTENER) {
  		nextstate = SSH_CHANNEL_OPENING;
  		rtype = "forwarded-streamlocal@openssh.com";
  	} else if (c->host_port == PORT_STREAMLOCAL) {
  		nextstate = SSH_CHANNEL_OPENING;
  		rtype = "direct-streamlocal@openssh.com";
  	} else if (c->host_port == 0) {
  		nextstate = SSH_CHANNEL_DYNAMIC;
  		rtype = "dynamic-tcpip";
  	} else {
  		nextstate = SSH_CHANNEL_OPENING;
  		rtype = "direct-tcpip";
  	}
  
  	addrlen = sizeof(addr);
  	newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  	if (newsock == -1) {
  		if (errno != EINTR && errno != EWOULDBLOCK &&
  		    errno != ECONNABORTED)
  			error("accept: %.100s", strerror(errno));
  		if (errno == EMFILE || errno == ENFILE)
  			c->notbefore = monotime() + 1;
  		return;
  	}
  	if (c->host_port != PORT_STREAMLOCAL)
  		set_nodelay(newsock);
  	nc = channel_new(ssh, rtype, nextstate, newsock, newsock, -1,
  	    c->local_window_max, c->local_maxpacket, 0, rtype, 1);
  	nc->listening_port = c->listening_port;
  	nc->host_port = c->host_port;
  	if (c->path != NULL)
  		nc->path = xstrdup(c->path);
  
  	if (nextstate != SSH_CHANNEL_DYNAMIC)
  		port_open_helper(ssh, nc, rtype);
  }
  
  /*
   * This is the authentication agent socket listening for connections from
   * clients.
   */
  static void
  channel_post_auth_listener(struct ssh *ssh, Channel *c)
  {
  	Channel *nc;
  	int r, newsock;
  	struct sockaddr_storage addr;
  	socklen_t addrlen;
  
  	if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
  		return;
  
  	addrlen = sizeof(addr);
  	newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  	if (newsock == -1) {
  		error("accept from auth socket: %.100s", strerror(errno));
  		if (errno == EMFILE || errno == ENFILE)
  			c->notbefore = monotime() + 1;
  		return;
  	}
  	nc = channel_new(ssh, "agent-connection",
  	    SSH_CHANNEL_OPENING, newsock, newsock, -1,
  	    c->local_window_max, c->local_maxpacket,
  	    0, "accepted auth socket", 1);
  	open_preamble(ssh, __func__, nc,
  	    c->agent_new ? "agent-connect" : "auth-agent@openssh.com");
  	if ((r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i", c->self);
  }
  
  static void
  channel_post_connecting(struct ssh *ssh, Channel *c)
  {
  	int err = 0, sock, isopen, r;
  	socklen_t sz = sizeof(err);
  
  	if ((c->io_ready & SSH_CHAN_IO_SOCK_W) == 0)
  		return;
  	if (!c->have_remote_id)
  		fatal_f("channel %d: no remote id", c->self);
  	/* for rdynamic the OPEN_CONFIRMATION has been sent already */
  	isopen = (c->type == SSH_CHANNEL_RDYNAMIC_FINISH);
  
  	if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, &err, &sz) == -1) {
  		err = errno;
  		error("getsockopt SO_ERROR failed");
  	}
  
  	if (err == 0) {
  		/* Non-blocking connection completed */
  		debug("channel %d: connected to %s port %d",
  		    c->self, c->connect_ctx.host, c->connect_ctx.port);
  		channel_connect_ctx_free(&c->connect_ctx);
  		c->type = SSH_CHANNEL_OPEN;
  		channel_set_used_time(ssh, c);
  		if (isopen) {
  			/* no message necessary */
  		} else {
  			if ((r = sshpkt_start(ssh,
  			    SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0 ||
  			    (r = sshpkt_send(ssh)) != 0)
  				fatal_fr(r, "channel %i open confirm", c->self);
  		}
  		return;
  	}
  	if (err == EINTR || err == EAGAIN || err == EINPROGRESS)
  		return;
  
  	/* Non-blocking connection failed */
  	debug("channel %d: connection failed: %s", c->self, strerror(err));
  
  	/* Try next address, if any */
  	if ((sock = connect_next(&c->connect_ctx)) == -1) {
  		/* Exhausted all addresses for this destination */
  		error("connect_to %.100s port %d: failed.",
  		    c->connect_ctx.host, c->connect_ctx.port);
  		channel_connect_ctx_free(&c->connect_ctx);
  		if (isopen) {
  			rdynamic_close(ssh, c);
  		} else {
  			if ((r = sshpkt_start(ssh,
  			    SSH2_MSG_CHANNEL_OPEN_FAILURE)) != 0 ||
  			    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  			    (r = sshpkt_put_u32(ssh,
  			    SSH2_OPEN_CONNECT_FAILED)) != 0 ||
  			    (r = sshpkt_put_cstring(ssh, strerror(err))) != 0 ||
  			    (r = sshpkt_put_cstring(ssh, "")) != 0 ||
  			    (r = sshpkt_send(ssh)) != 0)
  				fatal_fr(r, "channel %i: failure", c->self);
  			chan_mark_dead(ssh, c);
  		}
  	}
  
  	/* New non-blocking connection in progress */
  	close(c->sock);
  	c->sock = c->rfd = c->wfd = sock;
  }
  
  static int
  channel_handle_rfd(struct ssh *ssh, Channel *c)
  {
  	char buf[CHAN_RBUF];
  	ssize_t len;
  	int r;
  	size_t nr = 0, have, avail, maxlen = CHANNEL_MAX_READ;
  
  	if ((c->io_ready & SSH_CHAN_IO_RFD) == 0)
  		return 1; /* Shouldn't happen */
  	if ((avail = sshbuf_avail(c->input)) == 0)
  		return 1; /* Shouldn't happen */
  
  	/*
  	 * For "simple" channels (i.e. not datagram or filtered), we can
  	 * read directly to the channel buffer.
  	 */
  	if (c->input_filter == NULL && !c->datagram) {
  		/* Only OPEN channels have valid rwin */
  		if (c->type == SSH_CHANNEL_OPEN) {
  			if ((have = sshbuf_len(c->input)) >= c->remote_window)
  				return 1; /* shouldn't happen */
  			if (maxlen > c->remote_window - have)
  				maxlen = c->remote_window - have;
  		}
  		if (maxlen > avail)
  			maxlen = avail;
  		if ((r = sshbuf_read(c->rfd, c->input, maxlen, &nr)) != 0) {
  			if (errno == EINTR || errno == EAGAIN)
  				return 1;
  			debug2("channel %d: read failed rfd %d maxlen %zu: %s",
  			    c->self, c->rfd, maxlen, ssh_err(r));
  			goto rfail;
  		}
  		if (nr != 0)
  			channel_set_used_time(ssh, c);
  		return 1;
  	}
  
  	len = read(c->rfd, buf, sizeof(buf));
  	if (len == -1 && (errno == EINTR || errno == EAGAIN))
  		return 1;
  	if (len <= 0) {
  		debug2("channel %d: read<=0 rfd %d len %zd: %s",
  		    c->self, c->rfd, len,
  		    len == 0 ? "closed" : strerror(errno));
   rfail:
  		if (c->type != SSH_CHANNEL_OPEN) {
  			debug2("channel %d: not open", c->self);
  			chan_mark_dead(ssh, c);
  			return -1;
  		} else {
  			chan_read_failed(ssh, c);
  		}
  		return -1;
  	}
  	channel_set_used_time(ssh, c);
  	if (c->input_filter != NULL) {
  		if (c->input_filter(ssh, c, buf, len) == -1) {
  			debug2("channel %d: filter stops", c->self);
  			chan_read_failed(ssh, c);
  		}
  	} else if (c->datagram) {
  		if ((r = sshbuf_put_string(c->input, buf, len)) != 0)
  			fatal_fr(r, "channel %i: put datagram", c->self);
  	}
  	return 1;
  }
  
  static int
  channel_handle_wfd(struct ssh *ssh, Channel *c)
  {
  	struct termios tio;
  	u_char *data = NULL, *buf; /* XXX const; need filter API change */
  	size_t dlen, olen = 0;
  	int r, len;
  
  	if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
  		return 1;
  	if (sshbuf_len(c->output) == 0)
  		return 1;
  
  	/* Send buffered output data to the socket. */
  	olen = sshbuf_len(c->output);
  	if (c->output_filter != NULL) {
  		if ((buf = c->output_filter(ssh, c, &data, &dlen)) == NULL) {
  			debug2("channel %d: filter stops", c->self);
  			if (c->type != SSH_CHANNEL_OPEN)
  				chan_mark_dead(ssh, c);
  			else
  				chan_write_failed(ssh, c);
  			return -1;
  		}
  	} else if (c->datagram) {
  		if ((r = sshbuf_get_string(c->output, &data, &dlen)) != 0)
  			fatal_fr(r, "channel %i: get datagram", c->self);
  		buf = data;
  	} else {
  		buf = data = sshbuf_mutable_ptr(c->output);
  		dlen = sshbuf_len(c->output);
  	}
  
  	if (c->datagram) {
  		/* ignore truncated writes, datagrams might get lost */
  		len = write(c->wfd, buf, dlen);
  		free(data);
  		if (len == -1 && (errno == EINTR || errno == EAGAIN))
  			return 1;
  		if (len <= 0)
  			goto write_fail;
  		goto out;
  	}
  
  	len = write(c->wfd, buf, dlen);
  	if (len == -1 && (errno == EINTR || errno == EAGAIN))
  		return 1;
  	if (len <= 0) {
   write_fail:
  		if (c->type != SSH_CHANNEL_OPEN) {
  			debug2("channel %d: not open", c->self);
  			chan_mark_dead(ssh, c);
  			return -1;
  		} else {
  			chan_write_failed(ssh, c);
  		}
  		return -1;
  	}
  	channel_set_used_time(ssh, c);
  	if (c->isatty && dlen >= 1 && buf[0] != '\r') {
  		if (tcgetattr(c->wfd, &tio) == 0 &&
  		    !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
  			/*
  			 * Simulate echo to reduce the impact of
  			 * traffic analysis. We need to match the
  			 * size of a SSH2_MSG_CHANNEL_DATA message
  			 * (4 byte channel id + buf)
  			 */
  			if ((r = sshpkt_msg_ignore(ssh, 4+len)) != 0 ||
  			    (r = sshpkt_send(ssh)) != 0)
  				fatal_fr(r, "channel %i: ignore", c->self);
  		}
  	}
  	if ((r = sshbuf_consume(c->output, len)) != 0)
  		fatal_fr(r, "channel %i: consume", c->self);
   out:
  	c->local_consumed += olen - sshbuf_len(c->output);
  
  	return 1;
  }
  
  static int
  channel_handle_efd_write(struct ssh *ssh, Channel *c)
  {
  	int r;
  	ssize_t len;
  
  	if ((c->io_ready & SSH_CHAN_IO_EFD_W) == 0)
  		return 1;
  	if (sshbuf_len(c->extended) == 0)
  		return 1;
  
  	len = write(c->efd, sshbuf_ptr(c->extended),
  	    sshbuf_len(c->extended));
  	debug2("channel %d: written %zd to efd %d", c->self, len, c->efd);
  	if (len == -1 && (errno == EINTR || errno == EAGAIN))
  		return 1;
  	if (len <= 0) {
  		debug2("channel %d: closing write-efd %d", c->self, c->efd);
  		channel_close_fd(ssh, c, &c->efd);
  	} else {
  		if ((r = sshbuf_consume(c->extended, len)) != 0)
  			fatal_fr(r, "channel %i: consume", c->self);
  		c->local_consumed += len;
  		channel_set_used_time(ssh, c);
  	}
  	return 1;
  }
  
  static int
  channel_handle_efd_read(struct ssh *ssh, Channel *c)
  {
  	char buf[CHAN_RBUF];
  	int r;
  	ssize_t len;
  
  	if ((c->io_ready & SSH_CHAN_IO_EFD_R) == 0)
  		return 1;
  
  	len = read(c->efd, buf, sizeof(buf));
  	debug2("channel %d: read %zd from efd %d", c->self, len, c->efd);
  	if (len == -1 && (errno == EINTR || errno == EAGAIN))
  		return 1;
  	if (len <= 0) {
  		debug2("channel %d: closing read-efd %d", c->self, c->efd);
  		channel_close_fd(ssh, c, &c->efd);
  		return 1;
  	}
  	channel_set_used_time(ssh, c);
  	if (c->extended_usage == CHAN_EXTENDED_IGNORE)
  		debug3("channel %d: discard efd", c->self);
  	else if ((r = sshbuf_put(c->extended, buf, len)) != 0)
  		fatal_fr(r, "channel %i: append", c->self);
  	return 1;
  }
  
  static int
  channel_handle_efd(struct ssh *ssh, Channel *c)
  {
  	if (c->efd == -1)
  		return 1;
  
  	/** XXX handle drain efd, too */
  
  	if (c->extended_usage == CHAN_EXTENDED_WRITE)
  		return channel_handle_efd_write(ssh, c);
  	else if (c->extended_usage == CHAN_EXTENDED_READ ||
  	    c->extended_usage == CHAN_EXTENDED_IGNORE)
  		return channel_handle_efd_read(ssh, c);
  
  	return 1;
  }
  
  static int
  channel_check_window(struct ssh *ssh, Channel *c)
  {
  	int r;
  
  	if (c->type == SSH_CHANNEL_OPEN &&
  	    !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
  	    ((c->local_window_max - c->local_window >
  	    c->local_maxpacket*3) ||
  	    c->local_window < c->local_window_max/2) &&
  	    c->local_consumed > 0) {
  		if (!c->have_remote_id)
  			fatal_f("channel %d: no remote id", c->self);
  		if ((r = sshpkt_start(ssh,
  		    SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, c->local_consumed)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0) {
  			fatal_fr(r, "channel %i", c->self);
  		}
  		debug2("channel %d: window %d sent adjust %d", c->self,
  		    c->local_window, c->local_consumed);
  		c->local_window += c->local_consumed;
  		c->local_consumed = 0;
  	}
  	return 1;
  }
  
  static void
  channel_post_open(struct ssh *ssh, Channel *c)
  {
  	channel_handle_rfd(ssh, c);
  	channel_handle_wfd(ssh, c);
  	channel_handle_efd(ssh, c);
  	channel_check_window(ssh, c);
  }
  
  static u_int
  read_mux(struct ssh *ssh, Channel *c, u_int need)
  {
  	char buf[CHAN_RBUF];
  	ssize_t len;
  	u_int rlen;
  	int r;
  
  	if (sshbuf_len(c->input) < need) {
  		rlen = need - sshbuf_len(c->input);
  		len = read(c->rfd, buf, MINIMUM(rlen, CHAN_RBUF));
  		if (len == -1 && (errno == EINTR || errno == EAGAIN))
  			return sshbuf_len(c->input);
  		if (len <= 0) {
  			debug2("channel %d: ctl read<=0 rfd %d len %zd",
  			    c->self, c->rfd, len);
  			chan_read_failed(ssh, c);
  			return 0;
  		} else if ((r = sshbuf_put(c->input, buf, len)) != 0)
  			fatal_fr(r, "channel %i: append", c->self);
  	}
  	return sshbuf_len(c->input);
  }
  
  static void
  channel_post_mux_client_read(struct ssh *ssh, Channel *c)
  {
  	u_int need;
  
  	if ((c->io_ready & SSH_CHAN_IO_RFD) == 0)
  		return;
  	if (c->istate != CHAN_INPUT_OPEN && c->istate != CHAN_INPUT_WAIT_DRAIN)
  		return;
  	if (c->mux_pause)
  		return;
  
  	/*
  	 * Don't not read past the precise end of packets to
  	 * avoid disrupting fd passing.
  	 */
  	if (read_mux(ssh, c, 4) < 4) /* read header */
  		return;
  	/* XXX sshbuf_peek_u32 */
  	need = PEEK_U32(sshbuf_ptr(c->input));
  #define CHANNEL_MUX_MAX_PACKET	(256 * 1024)
  	if (need > CHANNEL_MUX_MAX_PACKET) {
  		debug2("channel %d: packet too big %u > %u",
  		    c->self, CHANNEL_MUX_MAX_PACKET, need);
  		chan_rcvd_oclose(ssh, c);
  		return;
  	}
  	if (read_mux(ssh, c, need + 4) < need + 4) /* read body */
  		return;
  	if (c->mux_rcb(ssh, c) != 0) {
  		debug("channel %d: mux_rcb failed", c->self);
  		chan_mark_dead(ssh, c);
  		return;
  	}
  }
  
  static void
  channel_post_mux_client_write(struct ssh *ssh, Channel *c)
  {
  	ssize_t len;
  	int r;
  
  	if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
  		return;
  	if (sshbuf_len(c->output) == 0)
  		return;
  
  	len = write(c->wfd, sshbuf_ptr(c->output), sshbuf_len(c->output));
  	if (len == -1 && (errno == EINTR || errno == EAGAIN))
  		return;
  	if (len <= 0) {
  		chan_mark_dead(ssh, c);
  		return;
  	}
  	if ((r = sshbuf_consume(c->output, len)) != 0)
  		fatal_fr(r, "channel %i: consume", c->self);
  }
  
  static void
  channel_post_mux_client(struct ssh *ssh, Channel *c)
  {
  	channel_post_mux_client_read(ssh, c);
  	channel_post_mux_client_write(ssh, c);
  }
  
  static void
  channel_post_mux_listener(struct ssh *ssh, Channel *c)
  {
  	Channel *nc;
  	struct sockaddr_storage addr;
  	socklen_t addrlen;
  	int newsock;
  	uid_t euid;
  	gid_t egid;
  
  	if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
  		return;
  
  	debug("multiplexing control connection");
  
  	/*
  	 * Accept connection on control socket
  	 */
  	memset(&addr, 0, sizeof(addr));
  	addrlen = sizeof(addr);
  	if ((newsock = accept(c->sock, (struct sockaddr*)&addr,
  	    &addrlen)) == -1) {
  		error_f("accept: %s", strerror(errno));
  		if (errno == EMFILE || errno == ENFILE)
  			c->notbefore = monotime() + 1;
  		return;
  	}
  
  	if (getpeereid(newsock, &euid, &egid) == -1) {
  		error_f("getpeereid failed: %s", strerror(errno));
  		close(newsock);
  		return;
  	}
  	if ((euid != 0) && (getuid() != euid)) {
  		error("multiplex uid mismatch: peer euid %u != uid %u",
  		    (u_int)euid, (u_int)getuid());
  		close(newsock);
  		return;
  	}
  	nc = channel_new(ssh, "mux-control", SSH_CHANNEL_MUX_CLIENT,
  	    newsock, newsock, -1, c->local_window_max,
  	    c->local_maxpacket, 0, "mux-control", 1);
  	nc->mux_rcb = c->mux_rcb;
  	debug3_f("new mux channel %d fd %d", nc->self, nc->sock);
  	/* establish state */
  	nc->mux_rcb(ssh, nc);
  	/* mux state transitions must not elicit protocol messages */
  	nc->flags |= CHAN_LOCAL;
  }
  
  static void
  channel_handler_init(struct ssh_channels *sc)
  {
  	chan_fn **pre, **post;
  
  	if ((pre = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*pre))) == NULL ||
  	    (post = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*post))) == NULL)
  		fatal_f("allocation failed");
  
  	pre[SSH_CHANNEL_OPEN] =			&channel_pre_open;
  	pre[SSH_CHANNEL_X11_OPEN] =		&channel_pre_x11_open;
  	pre[SSH_CHANNEL_PORT_LISTENER] =	&channel_pre_listener;
  	pre[SSH_CHANNEL_RPORT_LISTENER] =	&channel_pre_listener;
  	pre[SSH_CHANNEL_UNIX_LISTENER] =	&channel_pre_listener;
  	pre[SSH_CHANNEL_RUNIX_LISTENER] =	&channel_pre_listener;
  	pre[SSH_CHANNEL_X11_LISTENER] =		&channel_pre_listener;
  	pre[SSH_CHANNEL_AUTH_SOCKET] =		&channel_pre_listener;
  	pre[SSH_CHANNEL_CONNECTING] =		&channel_pre_connecting;
  	pre[SSH_CHANNEL_DYNAMIC] =		&channel_pre_dynamic;
  	pre[SSH_CHANNEL_RDYNAMIC_FINISH] =	&channel_pre_connecting;
  	pre[SSH_CHANNEL_MUX_LISTENER] =		&channel_pre_listener;
  	pre[SSH_CHANNEL_MUX_CLIENT] =		&channel_pre_mux_client;
  
  	post[SSH_CHANNEL_OPEN] =		&channel_post_open;
  	post[SSH_CHANNEL_PORT_LISTENER] =	&channel_post_port_listener;
  	post[SSH_CHANNEL_RPORT_LISTENER] =	&channel_post_port_listener;
  	post[SSH_CHANNEL_UNIX_LISTENER] =	&channel_post_port_listener;
  	post[SSH_CHANNEL_RUNIX_LISTENER] =	&channel_post_port_listener;
  	post[SSH_CHANNEL_X11_LISTENER] =	&channel_post_x11_listener;
  	post[SSH_CHANNEL_AUTH_SOCKET] =		&channel_post_auth_listener;
  	post[SSH_CHANNEL_CONNECTING] =		&channel_post_connecting;
  	post[SSH_CHANNEL_DYNAMIC] =		&channel_post_open;
  	post[SSH_CHANNEL_RDYNAMIC_FINISH] =	&channel_post_connecting;
  	post[SSH_CHANNEL_MUX_LISTENER] =	&channel_post_mux_listener;
  	post[SSH_CHANNEL_MUX_CLIENT] =		&channel_post_mux_client;
  
  	sc->channel_pre = pre;
  	sc->channel_post = post;
  }
  
  /* gc dead channels */
  static void
  channel_garbage_collect(struct ssh *ssh, Channel *c)
  {
  	if (c == NULL)
  		return;
  	if (c->detach_user != NULL) {
  		if (!chan_is_dead(ssh, c, c->detach_close))
  			return;
  
  		debug2("channel %d: gc: notify user", c->self);
  		c->detach_user(ssh, c->self, 0, NULL);
  		/* if we still have a callback */
  		if (c->detach_user != NULL)
  			return;
  		debug2("channel %d: gc: user detached", c->self);
  	}
  	if (!chan_is_dead(ssh, c, 1))
  		return;
  	debug2("channel %d: garbage collecting", c->self);
  	channel_free(ssh, c);
  }
  
  enum channel_table { CHAN_PRE, CHAN_POST };
  
  static void
  channel_handler(struct ssh *ssh, int table, struct timespec *timeout)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	chan_fn **ftab = table == CHAN_PRE ? sc->channel_pre : sc->channel_post;
  	u_int i, oalloc;
  	Channel *c;
  	time_t now;
  
  	now = monotime();
  	for (sc->nbulk = i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
  		c = sc->channels[i];
  		if (c == NULL)
  			continue;
  		/* Count open channels in bulk state */
  		if (c->type == SSH_CHANNEL_OPEN && c->bulk)
  			sc->nbulk++;
  		/* Try to keep IO going while rekeying */
  		if (ssh_packet_is_rekeying(ssh) && c->type != SSH_CHANNEL_OPEN)
  			continue;
  		if (c->delayed) {
  			if (table == CHAN_PRE)
  				c->delayed = 0;
  			else
  				continue;
  		}
  		if (ftab[c->type] != NULL) {
  			if (table == CHAN_PRE && c->type == SSH_CHANNEL_OPEN &&
  			    channel_get_expiry(ssh, c) != 0 &&
  			    now >= channel_get_expiry(ssh, c)) {
  				/* channel closed for inactivity */
  				verbose("channel %d: closing after %u seconds "
  				    "of inactivity", c->self,
  				    c->inactive_deadline);
  				channel_force_close(ssh, c, 1);
  			} else if (c->notbefore <= now) {
  				/* Run handlers that are not paused. */
  				(*ftab[c->type])(ssh, c);
  				/* inactivity timeouts must interrupt poll() */
  				if (timeout != NULL &&
  				    c->type == SSH_CHANNEL_OPEN &&
  				    channel_get_expiry(ssh, c) != 0) {
  					ptimeout_deadline_monotime(timeout,
  					    channel_get_expiry(ssh, c));
  				}
  			} else if (timeout != NULL) {
  				/*
  				 * Arrange for poll() wakeup when channel pause
  				 * timer expires.
  				 */
  				ptimeout_deadline_monotime(timeout,
  				    c->notbefore);
  			}
  		}
  		channel_garbage_collect(ssh, c);
  	}
  }
  
  /*
   * Create sockets before preparing IO.
   * This is necessary for things that need to happen after reading
   * the network-input but need to be completed before IO event setup, e.g.
   * because they may create new channels.
   */
  static void
  channel_before_prepare_io(struct ssh *ssh)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	Channel *c;
  	u_int i, oalloc;
  
  	for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
  		c = sc->channels[i];
  		if (c == NULL)
  			continue;
  		if (c->type == SSH_CHANNEL_RDYNAMIC_OPEN)
  			channel_before_prepare_io_rdynamic(ssh, c);
  	}
  }
  
  static void
  dump_channel_poll(const char *func, const char *what, Channel *c,
      u_int pollfd_offset, struct pollfd *pfd)
  {
  #ifdef DEBUG_CHANNEL_POLL
  	debug3("%s: channel %d: %s r%d w%d e%d s%d c->pfds [ %d %d %d %d ] "
  	    "io_want 0x%02x io_ready 0x%02x pfd[%u].fd=%d "
  	    "pfd.ev 0x%02x pfd.rev 0x%02x", func, c->self, what,
  	    c->rfd, c->wfd, c->efd, c->sock,
  	    c->pfds[0], c->pfds[1], c->pfds[2], c->pfds[3],
  	    c->io_want, c->io_ready,
  	    pollfd_offset, pfd->fd, pfd->events, pfd->revents);
  #endif
  }
  
  /* Prepare pollfd entries for a single channel */
  static void
  channel_prepare_pollfd(Channel *c, u_int *next_pollfd,
      struct pollfd *pfd, u_int npfd)
  {
  	u_int ev, p = *next_pollfd;
  
  	if (c == NULL)
  		return;
  	if (p + 4 > npfd) {
  		/* Shouldn't happen */
  		fatal_f("channel %d: bad pfd offset %u (max %u)",
  		    c->self, p, npfd);
  	}
  	c->pfds[0] = c->pfds[1] = c->pfds[2] = c->pfds[3] = -1;
  	/*
  	 * prepare c->rfd
  	 *
  	 * This is a special case, since c->rfd might be the same as
  	 * c->wfd, c->efd and/or c->sock. Handle those here if they want
  	 * IO too.
  	 */
  	if (c->rfd != -1) {
  		ev = 0;
  		if ((c->io_want & SSH_CHAN_IO_RFD) != 0)
  			ev |= POLLIN;
  		/* rfd == wfd */
  		if (c->wfd == c->rfd) {
  			if ((c->io_want & SSH_CHAN_IO_WFD) != 0)
  				ev |= POLLOUT;
  		}
  		/* rfd == efd */
  		if (c->efd == c->rfd) {
  			if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
  				ev |= POLLIN;
  			if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
  				ev |= POLLOUT;
  		}
  		/* rfd == sock */
  		if (c->sock == c->rfd) {
  			if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
  				ev |= POLLIN;
  			if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
  				ev |= POLLOUT;
  		}
  		/* Pack a pfd entry if any event armed for this fd */
  		if (ev != 0) {
  			c->pfds[0] = p;
  			pfd[p].fd = c->rfd;
  			pfd[p].events = ev;
  			dump_channel_poll(__func__, "rfd", c, p, &pfd[p]);
  			p++;
  		}
  	}
  	/* prepare c->wfd if wanting IO and not already handled above */
  	if (c->wfd != -1 && c->rfd != c->wfd) {
  		ev = 0;
  		if ((c->io_want & SSH_CHAN_IO_WFD))
  			ev |= POLLOUT;
  		/* Pack a pfd entry if any event armed for this fd */
  		if (ev != 0) {
  			c->pfds[1] = p;
  			pfd[p].fd = c->wfd;
  			pfd[p].events = ev;
  			dump_channel_poll(__func__, "wfd", c, p, &pfd[p]);
  			p++;
  		}
  	}
  	/* prepare c->efd if wanting IO and not already handled above */
  	if (c->efd != -1 && c->rfd != c->efd) {
  		ev = 0;
  		if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
  			ev |= POLLIN;
  		if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
  			ev |= POLLOUT;
  		/* Pack a pfd entry if any event armed for this fd */
  		if (ev != 0) {
  			c->pfds[2] = p;
  			pfd[p].fd = c->efd;
  			pfd[p].events = ev;
  			dump_channel_poll(__func__, "efd", c, p, &pfd[p]);
  			p++;
  		}
  	}
  	/* prepare c->sock if wanting IO and not already handled above */
  	if (c->sock != -1 && c->rfd != c->sock) {
  		ev = 0;
  		if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
  			ev |= POLLIN;
  		if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
  			ev |= POLLOUT;
  		/* Pack a pfd entry if any event armed for this fd */
  		if (ev != 0) {
  			c->pfds[3] = p;
  			pfd[p].fd = c->sock;
  			pfd[p].events = ev;
  			dump_channel_poll(__func__, "sock", c, p, &pfd[p]);
  			p++;
  		}
  	}
  	*next_pollfd = p;
  }
  
  /* * Allocate/prepare poll structure */
  void
  channel_prepare_poll(struct ssh *ssh, struct pollfd **pfdp, u_int *npfd_allocp,
      u_int *npfd_activep, u_int npfd_reserved, struct timespec *timeout)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	u_int i, oalloc, p, npfd = npfd_reserved;
  
  	channel_before_prepare_io(ssh); /* might create a new channel */
  	/* clear out I/O flags from last poll */
  	for (i = 0; i < sc->channels_alloc; i++) {
  		if (sc->channels[i] == NULL)
  			continue;
  		sc->channels[i]->io_want = sc->channels[i]->io_ready = 0;
  	}
  	/* Allocate 4x pollfd for each channel (rfd, wfd, efd, sock) */
  	if (sc->channels_alloc >= (INT_MAX / 4) - npfd_reserved)
  		fatal_f("too many channels"); /* shouldn't happen */
  	npfd += sc->channels_alloc * 4;
  	if (npfd > *npfd_allocp) {
  		*pfdp = xrecallocarray(*pfdp, *npfd_allocp,
  		    npfd, sizeof(**pfdp));
  		*npfd_allocp = npfd;
  	}
  	*npfd_activep = npfd_reserved;
  	oalloc = sc->channels_alloc;
  
  	channel_handler(ssh, CHAN_PRE, timeout);
  
  	if (oalloc != sc->channels_alloc) {
  		/* shouldn't happen */
  		fatal_f("channels_alloc changed during CHAN_PRE "
  		    "(was %u, now %u)", oalloc, sc->channels_alloc);
  	}
  
  	/* Prepare pollfd */
  	p = npfd_reserved;
  	for (i = 0; i < sc->channels_alloc; i++)
  		channel_prepare_pollfd(sc->channels[i], &p, *pfdp, npfd);
  	*npfd_activep = p;
  }
  
  static void
  fd_ready(Channel *c, int p, struct pollfd *pfds, u_int npfd, int fd,
      const char *what, u_int revents_mask, u_int ready)
  {
  	struct pollfd *pfd = &pfds[p];
  
  	if (fd == -1)
  		return;
  	if (p == -1 || (u_int)p >= npfd)
  		fatal_f("channel %d: bad pfd %d (max %u)", c->self, p, npfd);
  	dump_channel_poll(__func__, what, c, p, pfd);
  	if (pfd->fd != fd) {
  		fatal("channel %d: inconsistent %s fd=%d pollfd[%u].fd %d "
  		    "r%d w%d e%d s%d", c->self, what, fd, p, pfd->fd,
  		    c->rfd, c->wfd, c->efd, c->sock);
  	}
  	if ((pfd->revents & POLLNVAL) != 0) {
  		fatal("channel %d: invalid %s pollfd[%u].fd %d r%d w%d e%d s%d",
  		    c->self, what, p, pfd->fd, c->rfd, c->wfd, c->efd, c->sock);
  	}
  	if ((pfd->revents & (revents_mask|POLLHUP|POLLERR)) != 0)
  		c->io_ready |= ready & c->io_want;
  }
  
  /*
   * After poll, perform any appropriate operations for channels which have
   * events pending.
   */
  void
  channel_after_poll(struct ssh *ssh, struct pollfd *pfd, u_int npfd)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	u_int i;
  	int p;
  	Channel *c;
  
  #ifdef DEBUG_CHANNEL_POLL
  	for (p = 0; p < (int)npfd; p++) {
  		if (pfd[p].revents == 0)
  			continue;
  		debug_f("pfd[%u].fd %d rev 0x%04x",
  		    p, pfd[p].fd, pfd[p].revents);
  	}
  #endif
  
  	/* Convert pollfd into c->io_ready */
  	for (i = 0; i < sc->channels_alloc; i++) {
  		c = sc->channels[i];
  		if (c == NULL)
  			continue;
  		/* if rfd is shared with efd/sock then wfd should be too */
  		if (c->rfd != -1 && c->wfd != -1 && c->rfd != c->wfd &&
  		    (c->rfd == c->efd || c->rfd == c->sock)) {
  			/* Shouldn't happen */
  			fatal_f("channel %d: unexpected fds r%d w%d e%d s%d",
  			    c->self, c->rfd, c->wfd, c->efd, c->sock);
  		}
  		c->io_ready = 0;
  		/* rfd, potentially shared with wfd, efd and sock */
  		if (c->rfd != -1 && (p = c->pfds[0]) != -1) {
  			fd_ready(c, p, pfd, npfd, c->rfd,
  			    "rfd", POLLIN, SSH_CHAN_IO_RFD);
  			if (c->rfd == c->wfd) {
  				fd_ready(c, p, pfd, npfd, c->wfd,
  				    "wfd/r", POLLOUT, SSH_CHAN_IO_WFD);
  			}
  			if (c->rfd == c->efd) {
  				fd_ready(c, p, pfd, npfd, c->efd,
  				    "efdr/r", POLLIN, SSH_CHAN_IO_EFD_R);
  				fd_ready(c, p, pfd, npfd, c->efd,
  				    "efdw/r", POLLOUT, SSH_CHAN_IO_EFD_W);
  			}
  			if (c->rfd == c->sock) {
  				fd_ready(c, p, pfd, npfd, c->sock,
  				    "sockr/r", POLLIN, SSH_CHAN_IO_SOCK_R);
  				fd_ready(c, p, pfd, npfd, c->sock,
  				    "sockw/r", POLLOUT, SSH_CHAN_IO_SOCK_W);
  			}
  			dump_channel_poll(__func__, "rfd", c, p, pfd);
  		}
  		/* wfd */
  		if (c->wfd != -1 && c->wfd != c->rfd &&
  		    (p = c->pfds[1]) != -1) {
  			fd_ready(c, p, pfd, npfd, c->wfd,
  			    "wfd", POLLOUT, SSH_CHAN_IO_WFD);
  			dump_channel_poll(__func__, "wfd", c, p, pfd);
  		}
  		/* efd */
  		if (c->efd != -1 && c->efd != c->rfd &&
  		    (p = c->pfds[2]) != -1) {
  			fd_ready(c, p, pfd, npfd, c->efd,
  			    "efdr", POLLIN, SSH_CHAN_IO_EFD_R);
  			fd_ready(c, p, pfd, npfd, c->efd,
  			    "efdw", POLLOUT, SSH_CHAN_IO_EFD_W);
  			dump_channel_poll(__func__, "efd", c, p, pfd);
  		}
  		/* sock */
  		if (c->sock != -1 && c->sock != c->rfd &&
  		    (p = c->pfds[3]) != -1) {
  			fd_ready(c, p, pfd, npfd, c->sock,
  			    "sockr", POLLIN, SSH_CHAN_IO_SOCK_R);
  			fd_ready(c, p, pfd, npfd, c->sock,
  			    "sockw", POLLOUT, SSH_CHAN_IO_SOCK_W);
  			dump_channel_poll(__func__, "sock", c, p, pfd);
  		}
  	}
  	channel_handler(ssh, CHAN_POST, NULL);
  }
  
  /*
   * Enqueue data for channels with open or draining c->input.
   * Returns non-zero if a packet was enqueued.
   */
  static int
  channel_output_poll_input_open(struct ssh *ssh, Channel *c)
  {
  	size_t len, plen;
  	const u_char *pkt;
  	int r;
  
  	if ((len = sshbuf_len(c->input)) == 0) {
  		if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
  			/*
  			 * input-buffer is empty and read-socket shutdown:
  			 * tell peer, that we will not send more data:
  			 * send IEOF.
  			 * hack for extended data: delay EOF if EFD still
  			 * in use.
  			 */
  			if (CHANNEL_EFD_INPUT_ACTIVE(c))
  				debug2("channel %d: "
  				    "ibuf_empty delayed efd %d/(%zu)",
  				    c->self, c->efd, sshbuf_len(c->extended));
  			else
  				chan_ibuf_empty(ssh, c);
  		}
  		return 0;
  	}
  
  	if (!c->have_remote_id)
  		fatal_f("channel %d: no remote id", c->self);
  
  	if (c->datagram) {
  		/* Check datagram will fit; drop if not */
  		if ((r = sshbuf_get_string_direct(c->input, &pkt, &plen)) != 0)
  			fatal_fr(r, "channel %i: get datagram", c->self);
  		/*
  		 * XXX this does tail-drop on the datagram queue which is
  		 * usually suboptimal compared to head-drop. Better to have
  		 * backpressure at read time? (i.e. read + discard)
  		 */
  		if (plen > c->remote_window || plen > c->remote_maxpacket) {
  			debug("channel %d: datagram too big", c->self);
  			return 0;
  		}
  		/* Enqueue it */
  		if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  		    (r = sshpkt_put_string(ssh, pkt, plen)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0)
  			fatal_fr(r, "channel %i: send datagram", c->self);
  		c->remote_window -= plen;
  		return 1;
  	}
  
  	/* Enqueue packet for buffered data. */
  	if (len > c->remote_window)
  		len = c->remote_window;
  	if (len > c->remote_maxpacket)
  		len = c->remote_maxpacket;
  	if (len == 0)
  		return 0;
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  	    (r = sshpkt_put_string(ssh, sshbuf_ptr(c->input), len)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i: send data", c->self);
  	if ((r = sshbuf_consume(c->input, len)) != 0)
  		fatal_fr(r, "channel %i: consume", c->self);
  	c->remote_window -= len;
  	return 1;
  }
  
  /*
   * Enqueue data for channels with open c->extended in read mode.
   * Returns non-zero if a packet was enqueued.
   */
  static int
  channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
  {
  	size_t len;
  	int r;
  
  	if ((len = sshbuf_len(c->extended)) == 0)
  		return 0;
  
  	debug2("channel %d: rwin %u elen %zu euse %d", c->self,
  	    c->remote_window, sshbuf_len(c->extended), c->extended_usage);
  	if (len > c->remote_window)
  		len = c->remote_window;
  	if (len > c->remote_maxpacket)
  		len = c->remote_maxpacket;
  	if (len == 0)
  		return 0;
  	if (!c->have_remote_id)
  		fatal_f("channel %d: no remote id", c->self);
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, SSH2_EXTENDED_DATA_STDERR)) != 0 ||
  	    (r = sshpkt_put_string(ssh, sshbuf_ptr(c->extended), len)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "channel %i: data", c->self);
  	if ((r = sshbuf_consume(c->extended, len)) != 0)
  		fatal_fr(r, "channel %i: consume", c->self);
  	c->remote_window -= len;
  	debug2("channel %d: sent ext data %zu", c->self, len);
  	return 1;
  }
  
  /*
   * If there is data to send to the connection, enqueue some of it now.
   * Returns non-zero if data was enqueued.
   */
  int
  channel_output_poll(struct ssh *ssh)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	Channel *c;
  	u_int i;
  	int ret = 0;
  
  	for (i = 0; i < sc->channels_alloc; i++) {
  		c = sc->channels[i];
  		if (c == NULL)
  			continue;
  
  		/*
  		 * We are only interested in channels that can have buffered
  		 * incoming data.
  		 */
  		if (c->type != SSH_CHANNEL_OPEN)
  			continue;
  		if ((c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD))) {
  			/* XXX is this true? */
  			debug3("channel %d: will not send data after close",
  			    c->self);
  			continue;
  		}
  
  		/* Get the amount of buffered data for this channel. */
  		if (c->istate == CHAN_INPUT_OPEN ||
  		    c->istate == CHAN_INPUT_WAIT_DRAIN)
  			ret |= channel_output_poll_input_open(ssh, c);
  		/* Send extended data, i.e. stderr */
  		if (!(c->flags & CHAN_EOF_SENT) &&
  		    c->extended_usage == CHAN_EXTENDED_READ)
  			ret |= channel_output_poll_extended_read(ssh, c);
  	}
  	return ret;
  }
  
  /* -- mux proxy support  */
  
  /*
   * When multiplexing channel messages for mux clients we have to deal
   * with downstream messages from the mux client and upstream messages
   * from the ssh server:
   * 1) Handling downstream messages is straightforward and happens
   *    in channel_proxy_downstream():
   *    - We forward all messages (mostly) unmodified to the server.
   *    - However, in order to route messages from upstream to the correct
   *      downstream client, we have to replace the channel IDs used by the
   *      mux clients with a unique channel ID because the mux clients might
   *      use conflicting channel IDs.
   *    - so we inspect and change both SSH2_MSG_CHANNEL_OPEN and
   *      SSH2_MSG_CHANNEL_OPEN_CONFIRMATION messages, create a local
   *      SSH_CHANNEL_MUX_PROXY channel and replace the mux clients ID
   *      with the newly allocated channel ID.
   * 2) Upstream messages are received by matching SSH_CHANNEL_MUX_PROXY
   *    channels and processed by channel_proxy_upstream(). The local channel ID
   *    is then translated back to the original mux client ID.
   * 3) In both cases we need to keep track of matching SSH2_MSG_CHANNEL_CLOSE
   *    messages so we can clean up SSH_CHANNEL_MUX_PROXY channels.
   * 4) The SSH_CHANNEL_MUX_PROXY channels also need to closed when the
   *    downstream mux client are removed.
   * 5) Handling SSH2_MSG_CHANNEL_OPEN messages from the upstream server
   *    requires more work, because they are not addressed to a specific
   *    channel. E.g. client_request_forwarded_tcpip() needs to figure
   *    out whether the request is addressed to the local client or a
   *    specific downstream client based on the listen-address/port.
   * 6) Agent and X11-Forwarding have a similar problem and are currently
   *    not supported as the matching session/channel cannot be identified
   *    easily.
   */
  
  /*
   * receive packets from downstream mux clients:
   * channel callback fired on read from mux client, creates
   * SSH_CHANNEL_MUX_PROXY channels and translates channel IDs
   * on channel creation.
   */
  int
  channel_proxy_downstream(struct ssh *ssh, Channel *downstream)
  {
  	Channel *c = NULL;
  	struct sshbuf *original = NULL, *modified = NULL;
  	const u_char *cp;
  	char *ctype = NULL, *listen_host = NULL;
  	u_char type;
  	size_t have;
  	int ret = -1, r;
  	u_int id, remote_id, listen_port;
  
  	/* sshbuf_dump(downstream->input, stderr); */
  	if ((r = sshbuf_get_string_direct(downstream->input, &cp, &have))
  	    != 0) {
  		error_fr(r, "parse");
  		return -1;
  	}
  	if (have < 2) {
  		error_f("short message");
  		return -1;
  	}
  	type = cp[1];
  	/* skip padlen + type */
  	cp += 2;
  	have -= 2;
  	if (ssh_packet_log_type(type))
  		debug3_f("channel %u: down->up: type %u",
  		    downstream->self, type);
  
  	switch (type) {
  	case SSH2_MSG_CHANNEL_OPEN:
  		if ((original = sshbuf_from(cp, have)) == NULL ||
  		    (modified = sshbuf_new()) == NULL) {
  			error_f("alloc");
  			goto out;
  		}
  		if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0 ||
  		    (r = sshbuf_get_u32(original, &id)) != 0) {
  			error_fr(r, "parse");
  			goto out;
  		}
  		c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
  		    -1, -1, -1, 0, 0, 0, ctype, 1);
  		c->mux_ctx = downstream;	/* point to mux client */
  		c->mux_downstream_id = id;	/* original downstream id */
  		if ((r = sshbuf_put_cstring(modified, ctype)) != 0 ||
  		    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
  		    (r = sshbuf_putb(modified, original)) != 0) {
  			error_fr(r, "compose");
  			channel_free(ssh, c);
  			goto out;
  		}
  		break;
  	case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
  		/*
  		 * Almost the same as SSH2_MSG_CHANNEL_OPEN, except then we
  		 * need to parse 'remote_id' instead of 'ctype'.
  		 */
  		if ((original = sshbuf_from(cp, have)) == NULL ||
  		    (modified = sshbuf_new()) == NULL) {
  			error_f("alloc");
  			goto out;
  		}
  		if ((r = sshbuf_get_u32(original, &remote_id)) != 0 ||
  		    (r = sshbuf_get_u32(original, &id)) != 0) {
  			error_fr(r, "parse");
  			goto out;
  		}
  		c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
  		    -1, -1, -1, 0, 0, 0, "mux-down-connect", 1);
  		c->mux_ctx = downstream;	/* point to mux client */
  		c->mux_downstream_id = id;
  		c->remote_id = remote_id;
  		c->have_remote_id = 1;
  		if ((r = sshbuf_put_u32(modified, remote_id)) != 0 ||
  		    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
  		    (r = sshbuf_putb(modified, original)) != 0) {
  			error_fr(r, "compose");
  			channel_free(ssh, c);
  			goto out;
  		}
  		break;
  	case SSH2_MSG_GLOBAL_REQUEST:
  		if ((original = sshbuf_from(cp, have)) == NULL) {
  			error_f("alloc");
  			goto out;
  		}
  		if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0) {
  			error_fr(r, "parse");
  			goto out;
  		}
  		if (strcmp(ctype, "tcpip-forward") != 0) {
  			error_f("unsupported request %s", ctype);
  			goto out;
  		}
  		if ((r = sshbuf_get_u8(original, NULL)) != 0 ||
  		    (r = sshbuf_get_cstring(original, &listen_host, NULL)) != 0 ||
  		    (r = sshbuf_get_u32(original, &listen_port)) != 0) {
  			error_fr(r, "parse");
  			goto out;
  		}
  		if (listen_port > 65535) {
  			error_f("tcpip-forward for %s: bad port %u",
  			    listen_host, listen_port);
  			goto out;
  		}
  		/* Record that connection to this host/port is permitted. */
  		permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL, "<mux>",
  		    -1, listen_host, NULL, (int)listen_port, downstream);
  		break;
  	case SSH2_MSG_CHANNEL_CLOSE:
  		if (have < 4)
  			break;
  		remote_id = PEEK_U32(cp);
  		if ((c = channel_by_remote_id(ssh, remote_id)) != NULL) {
  			if (c->flags & CHAN_CLOSE_RCVD)
  				channel_free(ssh, c);
  			else
  				c->flags |= CHAN_CLOSE_SENT;
  		}
  		break;
  	}
  	if (modified) {
  		if ((r = sshpkt_start(ssh, type)) != 0 ||
  		    (r = sshpkt_putb(ssh, modified)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0) {
  			error_fr(r, "send");
  			goto out;
  		}
  	} else {
  		if ((r = sshpkt_start(ssh, type)) != 0 ||
  		    (r = sshpkt_put(ssh, cp, have)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0) {
  			error_fr(r, "send");
  			goto out;
  		}
  	}
  	ret = 0;
   out:
  	free(ctype);
  	free(listen_host);
  	sshbuf_free(original);
  	sshbuf_free(modified);
  	return ret;
  }
  
  /*
   * receive packets from upstream server and de-multiplex packets
   * to correct downstream:
   * implemented as a helper for channel input handlers,
   * replaces local (proxy) channel ID with downstream channel ID.
   */
  int
  channel_proxy_upstream(Channel *c, int type, uint32_t seq, struct ssh *ssh)
  {
  	struct sshbuf *b = NULL;
  	Channel *downstream;
  	const u_char *cp = NULL;
  	size_t len;
  	int r;
  
  	/*
  	 * When receiving packets from the peer we need to check whether we
  	 * need to forward the packets to the mux client. In this case we
  	 * restore the original channel id and keep track of CLOSE messages,
  	 * so we can cleanup the channel.
  	 */
  	if (c == NULL || c->type != SSH_CHANNEL_MUX_PROXY)
  		return 0;
  	if ((downstream = c->mux_ctx) == NULL)
  		return 0;
  	switch (type) {
  	case SSH2_MSG_CHANNEL_CLOSE:
  	case SSH2_MSG_CHANNEL_DATA:
  	case SSH2_MSG_CHANNEL_EOF:
  	case SSH2_MSG_CHANNEL_EXTENDED_DATA:
  	case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
  	case SSH2_MSG_CHANNEL_OPEN_FAILURE:
  	case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
  	case SSH2_MSG_CHANNEL_SUCCESS:
  	case SSH2_MSG_CHANNEL_FAILURE:
  	case SSH2_MSG_CHANNEL_REQUEST:
  		break;
  	default:
  		debug2_f("channel %u: unsupported type %u", c->self, type);
  		return 0;
  	}
  	if ((b = sshbuf_new()) == NULL) {
  		error_f("alloc reply");
  		goto out;
  	}
  	/* get remaining payload (after id) */
  	cp = sshpkt_ptr(ssh, &len);
  	if (cp == NULL) {
  		error_f("no packet");
  		goto out;
  	}
  	/* translate id and send to muxclient */
  	if ((r = sshbuf_put_u8(b, 0)) != 0 ||	/* padlen */
  	    (r = sshbuf_put_u8(b, type)) != 0 ||
  	    (r = sshbuf_put_u32(b, c->mux_downstream_id)) != 0 ||
  	    (r = sshbuf_put(b, cp, len)) != 0 ||
  	    (r = sshbuf_put_stringb(downstream->output, b)) != 0) {
  		error_fr(r, "compose muxclient");
  		goto out;
  	}
  	/* sshbuf_dump(b, stderr); */
  	if (ssh_packet_log_type(type))
  		debug3_f("channel %u: up->down: type %u", c->self, type);
   out:
  	/* update state */
  	switch (type) {
  	case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
  		/* record remote_id for SSH2_MSG_CHANNEL_CLOSE */
  		if (cp && len > 4) {
  			c->remote_id = PEEK_U32(cp);
  			c->have_remote_id = 1;
  		}
  		break;
  	case SSH2_MSG_CHANNEL_CLOSE:
  		if (c->flags & CHAN_CLOSE_SENT)
  			channel_free(ssh, c);
  		else
  			c->flags |= CHAN_CLOSE_RCVD;
  		break;
  	}
  	sshbuf_free(b);
  	return 1;
  }
  
  /* -- protocol input */
  
  /* Parse a channel ID from the current packet */
  static int
  channel_parse_id(struct ssh *ssh, const char *where, const char *what)
  {
  	uint32_t id;
  	int r;
  
  	if ((r = sshpkt_get_u32(ssh, &id)) != 0) {
  		error_r(r, "%s: parse id", where);
  		ssh_packet_disconnect(ssh, "Invalid %s message", what);
  	}
  	if (id > INT_MAX) {
  		error_r(r, "%s: bad channel id %u", where, id);
  		ssh_packet_disconnect(ssh, "Invalid %s channel id", what);
  	}
  	return (int)id;
  }
  
  /* Lookup a channel from an ID in the current packet */
  static Channel *
  channel_from_packet_id(struct ssh *ssh, const char *where, const char *what)
  {
  	int id = channel_parse_id(ssh, where, what);
  	Channel *c;
  
  	if ((c = channel_lookup(ssh, id)) == NULL) {
  		ssh_packet_disconnect(ssh,
  		    "%s packet referred to nonexistent channel %d", what, id);
  	}
  	return c;
  }
  
  int
  channel_input_data(int type, uint32_t seq, struct ssh *ssh)
  {
  	const u_char *data;
  	size_t data_len, win_len;
  	Channel *c = channel_from_packet_id(ssh, __func__, "data");
  	int r;
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  
  	/* Ignore any data for non-open channels (might happen on close) */
  	if (c->type != SSH_CHANNEL_OPEN &&
  	    c->type != SSH_CHANNEL_RDYNAMIC_OPEN &&
  	    c->type != SSH_CHANNEL_RDYNAMIC_FINISH &&
  	    c->type != SSH_CHANNEL_X11_OPEN)
  		return 0;
  
  	/* Get the data. */
  	if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
              (r = sshpkt_get_end(ssh)) != 0)
  		fatal_fr(r, "channel %i: get data", c->self);
  
  	win_len = data_len;
  	if (c->datagram)
  		win_len += 4;  /* string length header */
  
  	/*
  	 * The sending side reduces its window as it sends data, so we
  	 * must 'fake' consumption of the data in order to ensure that window
  	 * updates are sent back. Otherwise the connection might deadlock.
  	 */
  	if (c->ostate != CHAN_OUTPUT_OPEN) {
  		if (win_len > c->local_window)
  			c->local_window = 0;
  		else
  			c->local_window -= win_len;
  		c->local_consumed += win_len;
  		return 0;
  	}
  
  	if (win_len > c->local_maxpacket) {
  		logit("channel %d: rcvd big packet %zu, maxpack %u",
  		    c->self, win_len, c->local_maxpacket);
  		return 0;
  	}
  	if (win_len > c->local_window) {
  		c->local_window_exceeded += win_len - c->local_window;
  		logit("channel %d: rcvd too much data %zu, win %u/%u "
  		    "(excess %u)", c->self, win_len, c->local_window,
  		    c->local_window_max, c->local_window_exceeded);
  		c->local_window = 0;
  		/* Allow 10% grace before bringing the hammer down */
  		if (c->local_window_exceeded > (c->local_window_max / 10)) {
  			ssh_packet_disconnect(ssh, "channel %d: peer ignored "
  			    "channel window", c->self);
  		}
  	} else {
  		c->local_window -= win_len;
  		c->local_window_exceeded = 0;
  	}
  
  	if (c->datagram) {
  		if ((r = sshbuf_put_string(c->output, data, data_len)) != 0)
  			fatal_fr(r, "channel %i: append datagram", c->self);
  	} else if ((r = sshbuf_put(c->output, data, data_len)) != 0)
  		fatal_fr(r, "channel %i: append data", c->self);
  
  	return 0;
  }
  
  int
  channel_input_extended_data(int type, uint32_t seq, struct ssh *ssh)
  {
  	const u_char *data;
  	size_t data_len;
  	uint32_t tcode;
  	Channel *c = channel_from_packet_id(ssh, __func__, "extended data");
  	int r;
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  	if (c->type != SSH_CHANNEL_OPEN) {
  		logit("channel %d: ext data for non open", c->self);
  		return 0;
  	}
  	if (c->flags & CHAN_EOF_RCVD) {
  		if (ssh->compat & SSH_BUG_EXTEOF)
  			debug("channel %d: accepting ext data after eof",
  			    c->self);
  		else
  			ssh_packet_disconnect(ssh, "Received extended_data "
  			    "after EOF on channel %d.", c->self);
  	}
  
  	if ((r = sshpkt_get_u32(ssh, &tcode)) != 0) {
  		error_fr(r, "parse tcode");
  		ssh_packet_disconnect(ssh, "Invalid extended_data message");
  	}
  	if (c->efd == -1 ||
  	    c->extended_usage != CHAN_EXTENDED_WRITE ||
  	    tcode != SSH2_EXTENDED_DATA_STDERR) {
  		logit("channel %d: bad ext data", c->self);
  		return 0;
  	}
  	if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
              (r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "parse data");
  		ssh_packet_disconnect(ssh, "Invalid extended_data message");
  	}
  
  	if (data_len > c->local_window) {
  		logit("channel %d: rcvd too much extended_data %zu, win %u",
  		    c->self, data_len, c->local_window);
  		return 0;
  	}
  	debug2("channel %d: rcvd ext data %zu", c->self, data_len);
  	/* XXX sshpkt_getb? */
  	if ((r = sshbuf_put(c->extended, data, data_len)) != 0)
  		error_fr(r, "append");
  	c->local_window -= data_len;
  	return 0;
  }
  
  int
  channel_input_ieof(int type, uint32_t seq, struct ssh *ssh)
  {
  	Channel *c = channel_from_packet_id(ssh, __func__, "ieof");
  	int r;
  
          if ((r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "parse data");
  		ssh_packet_disconnect(ssh, "Invalid ieof message");
  	}
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  	chan_rcvd_ieof(ssh, c);
  
  	/* XXX force input close */
  	if (c->force_drain && c->istate == CHAN_INPUT_OPEN) {
  		debug("channel %d: FORCE input drain", c->self);
  		c->istate = CHAN_INPUT_WAIT_DRAIN;
  		if (sshbuf_len(c->input) == 0)
  			chan_ibuf_empty(ssh, c);
  	}
  	return 0;
  }
  
  int
  channel_input_oclose(int type, uint32_t seq, struct ssh *ssh)
  {
  	Channel *c = channel_from_packet_id(ssh, __func__, "oclose");
  	int r;
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
          if ((r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "parse data");
  		ssh_packet_disconnect(ssh, "Invalid oclose message");
  	}
  	chan_rcvd_oclose(ssh, c);
  	return 0;
  }
  
  int
  channel_input_open_confirmation(int type, uint32_t seq, struct ssh *ssh)
  {
  	Channel *c = channel_from_packet_id(ssh, __func__, "open confirmation");
  	uint32_t remote_window, remote_maxpacket;
  	int r;
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  	if (c->type != SSH_CHANNEL_OPENING)
  		ssh_packet_disconnect(ssh, "Received open confirmation for "
  		    "non-opening channel %d.", c->self);
  	/*
  	 * Record the remote channel number and mark that the channel
  	 * is now open.
  	 */
  	if ((r = sshpkt_get_u32(ssh, &c->remote_id)) != 0 ||
  	    (r = sshpkt_get_u32(ssh, &remote_window)) != 0 ||
  	    (r = sshpkt_get_u32(ssh, &remote_maxpacket)) != 0 ||
              (r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "window/maxpacket");
  		ssh_packet_disconnect(ssh, "Invalid open confirmation message");
  	}
  
  	c->have_remote_id = 1;
  	c->remote_window = remote_window;
  	c->remote_maxpacket = remote_maxpacket;
  	c->type = SSH_CHANNEL_OPEN;
  	if (c->open_confirm) {
  		debug2_f("channel %d: callback start", c->self);
  		c->open_confirm(ssh, c->self, 1, c->open_confirm_ctx);
  		debug2_f("channel %d: callback done", c->self);
  	}
  	channel_set_used_time(ssh, c);
  	debug2("channel %d: open confirm rwindow %u rmax %u", c->self,
  	    c->remote_window, c->remote_maxpacket);
  	return 0;
  }
  
  static char *
  reason2txt(int reason)
  {
  	switch (reason) {
  	case SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED:
  		return "administratively prohibited";
  	case SSH2_OPEN_CONNECT_FAILED:
  		return "connect failed";
  	case SSH2_OPEN_UNKNOWN_CHANNEL_TYPE:
  		return "unknown channel type";
  	case SSH2_OPEN_RESOURCE_SHORTAGE:
  		return "resource shortage";
  	}
  	return "unknown reason";
  }
  
  int
  channel_input_open_failure(int type, uint32_t seq, struct ssh *ssh)
  {
  	Channel *c = channel_from_packet_id(ssh, __func__, "open failure");
  	uint32_t reason;
  	char *msg = NULL;
  	int r;
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  	if (c->type != SSH_CHANNEL_OPENING)
  		ssh_packet_disconnect(ssh, "Received open failure for "
  		    "non-opening channel %d.", c->self);
  	if ((r = sshpkt_get_u32(ssh, &reason)) != 0) {
  		error_fr(r, "parse reason");
  		ssh_packet_disconnect(ssh, "Invalid open failure message");
  	}
  	/* skip language */
  	if ((r = sshpkt_get_cstring(ssh, &msg, NULL)) != 0 ||
  	    (r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0 ||
              (r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "parse msg/lang");
  		ssh_packet_disconnect(ssh, "Invalid open failure message");
  	}
  	logit("channel %d: open failed: %s%s%s", c->self,
  	    reason2txt(reason), msg ? ": ": "", msg ? msg : "");
  	free(msg);
  	if (c->open_confirm) {
  		debug2_f("channel %d: callback start", c->self);
  		c->open_confirm(ssh, c->self, 0, c->open_confirm_ctx);
  		debug2_f("channel %d: callback done", c->self);
  	}
  	/* Schedule the channel for cleanup/deletion. */
  	chan_mark_dead(ssh, c);
  	return 0;
  }
  
  int
  channel_input_window_adjust(int type, uint32_t seq, struct ssh *ssh)
  {
  	int id = channel_parse_id(ssh, __func__, "window adjust");
  	Channel *c;
  	uint32_t adjust;
  	u_int new_rwin;
  	int r;
  
  	if ((c = channel_lookup(ssh, id)) == NULL) {
  		logit("Received window adjust for non-open channel %d.", id);
  		return 0;
  	}
  
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
  	if ((r = sshpkt_get_u32(ssh, &adjust)) != 0 ||
              (r = sshpkt_get_end(ssh)) != 0) {
  		error_fr(r, "parse adjust");
  		ssh_packet_disconnect(ssh, "Invalid window adjust message");
  	}
  	debug2("channel %d: rcvd adjust %u", c->self, adjust);
  	if ((new_rwin = c->remote_window + adjust) < c->remote_window) {
  		fatal("channel %d: adjust %u overflows remote window %u",
  		    c->self, adjust, c->remote_window);
  	}
  	c->remote_window = new_rwin;
  	return 0;
  }
  
  int
  channel_input_status_confirm(int type, uint32_t seq, struct ssh *ssh)
  {
  	int id = channel_parse_id(ssh, __func__, "status confirm");
  	Channel *c;
  	struct channel_confirm *cc;
  
  	/* Reset keepalive timeout */
  	ssh_packet_set_alive_timeouts(ssh, 0);
  
  	debug2_f("type %d id %d", type, id);
  
  	if ((c = channel_lookup(ssh, id)) == NULL) {
  		logit_f("%d: unknown", id);
  		return 0;
  	}
  	if (channel_proxy_upstream(c, type, seq, ssh))
  		return 0;
          if (sshpkt_get_end(ssh) != 0)
  		ssh_packet_disconnect(ssh, "Invalid status confirm message");
  	if ((cc = TAILQ_FIRST(&c->status_confirms)) == NULL)
  		return 0;
  	cc->cb(ssh, type, c, cc->ctx);
  	TAILQ_REMOVE(&c->status_confirms, cc, entry);
  	freezero(cc, sizeof(*cc));
  	return 0;
  }
  
  /* -- tcp forwarding */
  
  void
  channel_set_af(struct ssh *ssh, int af)
  {
  	ssh->chanctxt->IPv4or6 = af;
  }
  
  
  /*
   * Determine whether or not a port forward listens to loopback, the
   * specified address or wildcard. On the client, a specified bind
   * address will always override gateway_ports. On the server, a
   * gateway_ports of 1 (``yes'') will override the client's specification
   * and force a wildcard bind, whereas a value of 2 (``clientspecified'')
   * will bind to whatever address the client asked for.
   *
   * Special-case listen_addrs are:
   *
   * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
   * "" (empty string), "*"  -> wildcard v4/v6
   * "localhost"             -> loopback v4/v6
   * "127.0.0.1" / "::1"     -> accepted even if gateway_ports isn't set
   */
  static const char *
  channel_fwd_bind_addr(struct ssh *ssh, const char *listen_addr, int *wildcardp,
      int is_client, struct ForwardOptions *fwd_opts)
  {
  	const char *addr = NULL;
  	int wildcard = 0;
  
  	if (listen_addr == NULL) {
  		/* No address specified: default to gateway_ports setting */
  		if (fwd_opts->gateway_ports)
  			wildcard = 1;
  	} else if (fwd_opts->gateway_ports || is_client) {
  		if (((ssh->compat & SSH_OLD_FORWARD_ADDR) &&
  		    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
  		    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
  		    (!is_client && fwd_opts->gateway_ports == 1)) {
  			wildcard = 1;
  			/*
  			 * Notify client if they requested a specific listen
  			 * address and it was overridden.
  			 */
  			if (*listen_addr != '\0' &&
  			    strcmp(listen_addr, "0.0.0.0") != 0 &&
  			    strcmp(listen_addr, "*") != 0) {
  				ssh_packet_send_debug(ssh,
  				    "Forwarding listen address "
  				    "\"%s\" overridden by server "
  				    "GatewayPorts", listen_addr);
  			}
  		} else if (strcmp(listen_addr, "localhost") != 0 ||
  		    strcmp(listen_addr, "127.0.0.1") == 0 ||
  		    strcmp(listen_addr, "::1") == 0) {
  			/*
  			 * Accept explicit localhost address when
  			 * GatewayPorts=yes. The "localhost" hostname is
  			 * deliberately skipped here so it will listen on all
  			 * available local address families.
  			 */
  			addr = listen_addr;
  		}
  	} else if (strcmp(listen_addr, "127.0.0.1") == 0 ||
  	    strcmp(listen_addr, "::1") == 0) {
  		/*
  		 * If a specific IPv4/IPv6 localhost address has been
  		 * requested then accept it even if gateway_ports is in
  		 * effect. This allows the client to prefer IPv4 or IPv6.
  		 */
  		addr = listen_addr;
  	}
  	if (wildcardp != NULL)
  		*wildcardp = wildcard;
  	return addr;
  }
  
  static int
  channel_setup_fwd_listener_tcpip(struct ssh *ssh, int type,
      struct Forward *fwd, int *allocated_listen_port,
      struct ForwardOptions *fwd_opts)
  {
  	Channel *c;
  	int sock, r, success = 0, wildcard = 0, is_client;
  	struct addrinfo hints, *ai, *aitop;
  	const char *host, *addr;
  	char ntop[NI_MAXHOST], strport[NI_MAXSERV];
  	in_port_t *lport_p;
  
  	is_client = (type == SSH_CHANNEL_PORT_LISTENER);
  
  	if (is_client && fwd->connect_path != NULL) {
  		host = fwd->connect_path;
  	} else {
  		host = (type == SSH_CHANNEL_RPORT_LISTENER) ?
  		    fwd->listen_host : fwd->connect_host;
  		if (host == NULL) {
  			error("No forward host name.");
  			return 0;
  		}
  		if (strlen(host) >= NI_MAXHOST) {
  			error("Forward host name too long.");
  			return 0;
  		}
  	}
  
  	/* Determine the bind address, cf. channel_fwd_bind_addr() comment */
  	addr = channel_fwd_bind_addr(ssh, fwd->listen_host, &wildcard,
  	    is_client, fwd_opts);
  	debug3_f("type %d wildcard %d addr %s", type, wildcard,
  	    (addr == NULL) ? "NULL" : addr);
  
  	/*
  	 * getaddrinfo returns a loopback address if the hostname is
  	 * set to NULL and hints.ai_flags is not AI_PASSIVE
  	 */
  	memset(&hints, 0, sizeof(hints));
  	hints.ai_family = ssh->chanctxt->IPv4or6;
  	hints.ai_flags = wildcard ? AI_PASSIVE : 0;
  	hints.ai_socktype = SOCK_STREAM;
  	snprintf(strport, sizeof strport, "%d", fwd->listen_port);
  	if ((r = getaddrinfo(addr, strport, &hints, &aitop)) != 0) {
  		if (addr == NULL) {
  			/* This really shouldn't happen */
  			ssh_packet_disconnect(ssh, "getaddrinfo: fatal error: %s",
  			    ssh_gai_strerror(r));
  		} else {
  			error_f("getaddrinfo(%.64s): %s", addr,
  			    ssh_gai_strerror(r));
  		}
  		return 0;
  	}
  	if (allocated_listen_port != NULL)
  		*allocated_listen_port = 0;
  	for (ai = aitop; ai; ai = ai->ai_next) {
  		switch (ai->ai_family) {
  		case AF_INET:
  			lport_p = &((struct sockaddr_in *)ai->ai_addr)->
  			    sin_port;
  			break;
  		case AF_INET6:
  			lport_p = &((struct sockaddr_in6 *)ai->ai_addr)->
  			    sin6_port;
  			break;
  		default:
  			continue;
  		}
  		/*
  		 * If allocating a port for -R forwards, then use the
  		 * same port for all address families.
  		 */
  		if (type == SSH_CHANNEL_RPORT_LISTENER &&
  		    fwd->listen_port == 0 && allocated_listen_port != NULL &&
  		    *allocated_listen_port > 0)
  			*lport_p = htons(*allocated_listen_port);
  
  		if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
  		    strport, sizeof(strport),
  		    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
  			error_f("getnameinfo failed");
  			continue;
  		}
  		/* Create a port to listen for the host. */
  		sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
  		if (sock == -1) {
  			/* this is no error since kernel may not support ipv6 */
  			verbose("socket [%s]:%s: %.100s", ntop, strport,
  			    strerror(errno));
  			continue;
  		}
  
  		set_reuseaddr(sock);
  
  		debug("Local forwarding listening on %s port %s.",
  		    ntop, strport);
  
  		/* Bind the socket to the address. */
  		if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
  			/*
  			 * address can be in if use ipv6 address is
  			 * already bound
  			 */
  			verbose("bind [%s]:%s: %.100s",
  			    ntop, strport, strerror(errno));
  			close(sock);
  			continue;
  		}
  		/* Start listening for connections on the socket. */
  		if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
  			error("listen [%s]:%s: %.100s", ntop, strport,
  			    strerror(errno));
  			close(sock);
  			continue;
  		}
  
  		/*
  		 * fwd->listen_port == 0 requests a dynamically allocated port -
  		 * record what we got.
  		 */
  		if (type == SSH_CHANNEL_RPORT_LISTENER &&
  		    fwd->listen_port == 0 &&
  		    allocated_listen_port != NULL &&
  		    *allocated_listen_port == 0) {
  			*allocated_listen_port = get_local_port(sock);
  			debug("Allocated listen port %d",
  			    *allocated_listen_port);
  		}
  
  		/* Allocate a channel number for the socket. */
  		c = channel_new(ssh, "port-listener", type, sock, sock, -1,
  		    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
  		    0, "port listener", 1);
  		c->path = xstrdup(host);
  		c->host_port = fwd->connect_port;
  		c->listening_addr = addr == NULL ? NULL : xstrdup(addr);
  		if (fwd->listen_port == 0 && allocated_listen_port != NULL &&
  		    !(ssh->compat & SSH_BUG_DYNAMIC_RPORT))
  			c->listening_port = *allocated_listen_port;
  		else
  			c->listening_port = fwd->listen_port;
  		success = 1;
  	}
  	if (success == 0)
  		error_f("cannot listen to port: %d", fwd->listen_port);
  	freeaddrinfo(aitop);
  	return success;
  }
  
  static int
  channel_setup_fwd_listener_streamlocal(struct ssh *ssh, int type,
      struct Forward *fwd, struct ForwardOptions *fwd_opts)
  {
  	struct sockaddr_un sunaddr;
  	const char *path;
  	Channel *c;
  	int port, sock;
  	mode_t omask;
  
  	switch (type) {
  	case SSH_CHANNEL_UNIX_LISTENER:
  		if (fwd->connect_path != NULL) {
  			if (strlen(fwd->connect_path) > sizeof(sunaddr.sun_path)) {
  				error("Local connecting path too long: %s",
  				    fwd->connect_path);
  				return 0;
  			}
  			path = fwd->connect_path;
  			port = PORT_STREAMLOCAL;
  		} else {
  			if (fwd->connect_host == NULL) {
  				error("No forward host name.");
  				return 0;
  			}
  			if (strlen(fwd->connect_host) >= NI_MAXHOST) {
  				error("Forward host name too long.");
  				return 0;
  			}
  			path = fwd->connect_host;
  			port = fwd->connect_port;
  		}
  		break;
  	case SSH_CHANNEL_RUNIX_LISTENER:
  		path = fwd->listen_path;
  		port = PORT_STREAMLOCAL;
  		break;
  	default:
  		error_f("unexpected channel type %d", type);
  		return 0;
  	}
  
  	if (fwd->listen_path == NULL) {
  		error("No forward path name.");
  		return 0;
  	}
  	if (strlen(fwd->listen_path) > sizeof(sunaddr.sun_path)) {
  		error("Local listening path too long: %s", fwd->listen_path);
  		return 0;
  	}
  
  	debug3_f("type %d path %s", type, fwd->listen_path);
  
  	/* Start a Unix domain listener. */
  	omask = umask(fwd_opts->streamlocal_bind_mask);
  	sock = unix_listener(fwd->listen_path, SSH_LISTEN_BACKLOG,
  	    fwd_opts->streamlocal_bind_unlink);
  	umask(omask);
  	if (sock < 0)
  		return 0;
  
  	debug("Local forwarding listening on path %s.", fwd->listen_path);
  
  	/* Allocate a channel number for the socket. */
  	c = channel_new(ssh, "unix-listener", type, sock, sock, -1,
  	    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
  	    0, "unix listener", 1);
  	c->path = xstrdup(path);
  	c->host_port = port;
  	c->listening_port = PORT_STREAMLOCAL;
  	c->listening_addr = xstrdup(fwd->listen_path);
  	return 1;
  }
  
  static int
  channel_cancel_rport_listener_tcpip(struct ssh *ssh,
      const char *host, u_short port)
  {
  	u_int i;
  	int found = 0;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		Channel *c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
  			continue;
  		if (strcmp(c->path, host) == 0 && c->listening_port == port) {
  			debug2_f("close channel %d", i);
  			channel_free(ssh, c);
  			found = 1;
  		}
  	}
  
  	return found;
  }
  
  static int
  channel_cancel_rport_listener_streamlocal(struct ssh *ssh, const char *path)
  {
  	u_int i;
  	int found = 0;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		Channel *c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_RUNIX_LISTENER)
  			continue;
  		if (c->path == NULL)
  			continue;
  		if (strcmp(c->path, path) == 0) {
  			debug2_f("close channel %d", i);
  			channel_free(ssh, c);
  			found = 1;
  		}
  	}
  
  	return found;
  }
  
  int
  channel_cancel_rport_listener(struct ssh *ssh, struct Forward *fwd)
  {
  	if (fwd->listen_path != NULL) {
  		return channel_cancel_rport_listener_streamlocal(ssh,
  		    fwd->listen_path);
  	} else {
  		return channel_cancel_rport_listener_tcpip(ssh,
  		    fwd->listen_host, fwd->listen_port);
  	}
  }
  
  static int
  channel_cancel_lport_listener_tcpip(struct ssh *ssh,
      const char *lhost, u_short lport, int cport,
      struct ForwardOptions *fwd_opts)
  {
  	u_int i;
  	int found = 0;
  	const char *addr = channel_fwd_bind_addr(ssh, lhost, NULL, 1, fwd_opts);
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		Channel *c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_PORT_LISTENER)
  			continue;
  		if (c->listening_port != lport)
  			continue;
  		if (cport == CHANNEL_CANCEL_PORT_STATIC) {
  			/* skip dynamic forwardings */
  			if (c->host_port == 0)
  				continue;
  		} else {
  			if (c->host_port != cport)
  				continue;
  		}
  		if ((c->listening_addr == NULL && addr != NULL) ||
  		    (c->listening_addr != NULL && addr == NULL))
  			continue;
  		if (addr == NULL || strcmp(c->listening_addr, addr) == 0) {
  			debug2_f("close channel %d", i);
  			channel_free(ssh, c);
  			found = 1;
  		}
  	}
  
  	return found;
  }
  
  static int
  channel_cancel_lport_listener_streamlocal(struct ssh *ssh, const char *path)
  {
  	u_int i;
  	int found = 0;
  
  	if (path == NULL) {
  		error_f("no path specified.");
  		return 0;
  	}
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		Channel *c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->type != SSH_CHANNEL_UNIX_LISTENER)
  			continue;
  		if (c->listening_addr == NULL)
  			continue;
  		if (strcmp(c->listening_addr, path) == 0) {
  			debug2_f("close channel %d", i);
  			channel_free(ssh, c);
  			found = 1;
  		}
  	}
  
  	return found;
  }
  
  int
  channel_cancel_lport_listener(struct ssh *ssh,
      struct Forward *fwd, int cport, struct ForwardOptions *fwd_opts)
  {
  	if (fwd->listen_path != NULL) {
  		return channel_cancel_lport_listener_streamlocal(ssh,
  		    fwd->listen_path);
  	} else {
  		return channel_cancel_lport_listener_tcpip(ssh,
  		    fwd->listen_host, fwd->listen_port, cport, fwd_opts);
  	}
  }
  
  /* protocol local port fwd, used by ssh */
  int
  channel_setup_local_fwd_listener(struct ssh *ssh,
      struct Forward *fwd, struct ForwardOptions *fwd_opts)
  {
  	if (fwd->listen_path != NULL) {
  		return channel_setup_fwd_listener_streamlocal(ssh,
  		    SSH_CHANNEL_UNIX_LISTENER, fwd, fwd_opts);
  	} else {
  		return channel_setup_fwd_listener_tcpip(ssh,
  		    SSH_CHANNEL_PORT_LISTENER, fwd, NULL, fwd_opts);
  	}
  }
  
  /* Matches a remote forwarding permission against a requested forwarding */
  static int
  remote_open_match(struct permission *allowed_open, struct Forward *fwd)
  {
  	int ret;
  	char *lhost;
  
  	/* XXX add ACLs for streamlocal */
  	if (fwd->listen_path != NULL)
  		return 1;
  
  	if (fwd->listen_host == NULL || allowed_open->listen_host == NULL)
  		return 0;
  
  	if (allowed_open->listen_port != FWD_PERMIT_ANY_PORT &&
  	    allowed_open->listen_port != fwd->listen_port)
  		return 0;
  
  	/* Match hostnames case-insensitively */
  	lhost = xstrdup(fwd->listen_host);
  	lowercase(lhost);
  	ret = match_pattern(lhost, allowed_open->listen_host);
  	free(lhost);
  
  	return ret;
  }
  
  /* Checks whether a requested remote forwarding is permitted */
  static int
  check_rfwd_permission(struct ssh *ssh, struct Forward *fwd)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->remote_perms;
  	u_int i, permit, permit_adm = 1;
  	struct permission *perm;
  
  	/* XXX apply GatewayPorts override before checking? */
  
  	permit = pset->all_permitted;
  	if (!permit) {
  		for (i = 0; i < pset->num_permitted_user; i++) {
  			perm = &pset->permitted_user[i];
  			if (remote_open_match(perm, fwd)) {
  				permit = 1;
  				break;
  			}
  		}
  	}
  
  	if (pset->num_permitted_admin > 0) {
  		permit_adm = 0;
  		for (i = 0; i < pset->num_permitted_admin; i++) {
  			perm = &pset->permitted_admin[i];
  			if (remote_open_match(perm, fwd)) {
  				permit_adm = 1;
  				break;
  			}
  		}
  	}
  
  	return permit && permit_adm;
  }
  
  /* protocol v2 remote port fwd, used by sshd */
  int
  channel_setup_remote_fwd_listener(struct ssh *ssh, struct Forward *fwd,
      int *allocated_listen_port, struct ForwardOptions *fwd_opts)
  {
  	if (!check_rfwd_permission(ssh, fwd)) {
  		ssh_packet_send_debug(ssh, "port forwarding refused");
  		if (fwd->listen_path != NULL)
  			/* XXX always allowed, see remote_open_match() */
  			logit("Received request from %.100s port %d to "
  			    "remote forward to path \"%.100s\", "
  			    "but the request was denied.",
  			    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
  			    fwd->listen_path);
  		else if(fwd->listen_host != NULL)
  			logit("Received request from %.100s port %d to "
  			    "remote forward to host %.100s port %d, "
  			    "but the request was denied.",
  			    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
  			    fwd->listen_host, fwd->listen_port );
  		else
  			logit("Received request from %.100s port %d to remote "
  			    "forward, but the request was denied.",
  			    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
  		return 0;
  	}
  	if (fwd->listen_path != NULL) {
  		return channel_setup_fwd_listener_streamlocal(ssh,
  		    SSH_CHANNEL_RUNIX_LISTENER, fwd, fwd_opts);
  	} else {
  		return channel_setup_fwd_listener_tcpip(ssh,
  		    SSH_CHANNEL_RPORT_LISTENER, fwd, allocated_listen_port,
  		    fwd_opts);
  	}
  }
  
  /*
   * Translate the requested rfwd listen host to something usable for
   * this server.
   */
  static const char *
  channel_rfwd_bind_host(const char *listen_host)
  {
  	if (listen_host == NULL) {
  		return "localhost";
  	} else if (*listen_host == '\0' || strcmp(listen_host, "*") == 0) {
  		return "";
  	} else
  		return listen_host;
  }
  
  /*
   * Initiate forwarding of connections to port "port" on remote host through
   * the secure channel to host:port from local side.
   * Returns handle (index) for updating the dynamic listen port with
   * channel_update_permission().
   */
  int
  channel_request_remote_forwarding(struct ssh *ssh, struct Forward *fwd)
  {
  	int r, success = 0, idx = -1;
  	const char *host_to_connect, *listen_host, *listen_path;
  	int port_to_connect, listen_port;
  
  	/* Send the forward request to the remote side. */
  	if (fwd->listen_path != NULL) {
  		if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
  		    (r = sshpkt_put_cstring(ssh,
  		    "streamlocal-forward@openssh.com")) != 0 ||
  		    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
  		    (r = sshpkt_put_cstring(ssh, fwd->listen_path)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0 ||
  		    (r = ssh_packet_write_wait(ssh)) != 0)
  			fatal_fr(r, "request streamlocal");
  	} else {
  		if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
  		    (r = sshpkt_put_cstring(ssh, "tcpip-forward")) != 0 ||
  		    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
  		    (r = sshpkt_put_cstring(ssh,
  		    channel_rfwd_bind_host(fwd->listen_host))) != 0 ||
  		    (r = sshpkt_put_u32(ssh, fwd->listen_port)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0 ||
  		    (r = ssh_packet_write_wait(ssh)) != 0)
  			fatal_fr(r, "request tcpip-forward");
  	}
  	/* Assume that server accepts the request */
  	success = 1;
  	if (success) {
  		/* Record that connection to this host/port is permitted. */
  		host_to_connect = listen_host = listen_path = NULL;
  		port_to_connect = listen_port = 0;
  		if (fwd->connect_path != NULL) {
  			host_to_connect = fwd->connect_path;
  			port_to_connect = PORT_STREAMLOCAL;
  		} else {
  			host_to_connect = fwd->connect_host;
  			port_to_connect = fwd->connect_port;
  		}
  		if (fwd->listen_path != NULL) {
  			listen_path = fwd->listen_path;
  			listen_port = PORT_STREAMLOCAL;
  		} else {
  			listen_host = fwd->listen_host;
  			listen_port = fwd->listen_port;
  		}
  		idx = permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL,
  		    host_to_connect, port_to_connect,
  		    listen_host, listen_path, listen_port, NULL);
  	}
  	return idx;
  }
  
  static int
  open_match(struct permission *allowed_open, const char *requestedhost,
      int requestedport)
  {
  	if (allowed_open->host_to_connect == NULL)
  		return 0;
  	if (allowed_open->port_to_connect != FWD_PERMIT_ANY_PORT &&
  	    allowed_open->port_to_connect != requestedport)
  		return 0;
  	if (strcmp(allowed_open->host_to_connect, FWD_PERMIT_ANY_HOST) != 0 &&
  	    strcmp(allowed_open->host_to_connect, requestedhost) != 0)
  		return 0;
  	return 1;
  }
  
  /*
   * Note that in the listen host/port case
   * we don't support FWD_PERMIT_ANY_PORT and
   * need to translate between the configured-host (listen_host)
   * and what we've sent to the remote server (channel_rfwd_bind_host)
   */
  static int
  open_listen_match_tcpip(struct permission *allowed_open,
      const char *requestedhost, u_short requestedport, int translate)
  {
  	const char *allowed_host;
  
  	if (allowed_open->host_to_connect == NULL)
  		return 0;
  	if (allowed_open->listen_port != requestedport)
  		return 0;
  	if (!translate && allowed_open->listen_host == NULL &&
  	    requestedhost == NULL)
  		return 1;
  	allowed_host = translate ?
  	    channel_rfwd_bind_host(allowed_open->listen_host) :
  	    allowed_open->listen_host;
  	if (allowed_host == NULL || requestedhost == NULL ||
  	    strcmp(allowed_host, requestedhost) != 0)
  		return 0;
  	return 1;
  }
  
  static int
  open_listen_match_streamlocal(struct permission *allowed_open,
      const char *requestedpath)
  {
  	if (allowed_open->host_to_connect == NULL)
  		return 0;
  	if (allowed_open->listen_port != PORT_STREAMLOCAL)
  		return 0;
  	if (allowed_open->listen_path == NULL ||
  	    strcmp(allowed_open->listen_path, requestedpath) != 0)
  		return 0;
  	return 1;
  }
  
  /*
   * Request cancellation of remote forwarding of connection host:port from
   * local side.
   */
  static int
  channel_request_rforward_cancel_tcpip(struct ssh *ssh,
      const char *host, u_short port)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	int r;
  	u_int i;
  	struct permission *perm = NULL;
  
  	for (i = 0; i < pset->num_permitted_user; i++) {
  		perm = &pset->permitted_user[i];
  		if (open_listen_match_tcpip(perm, host, port, 0))
  			break;
  		perm = NULL;
  	}
  	if (perm == NULL) {
  		debug_f("requested forward not found");
  		return -1;
  	}
  	if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
  	    (r = sshpkt_put_cstring(ssh, "cancel-tcpip-forward")) != 0 ||
  	    (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
  	    (r = sshpkt_put_cstring(ssh, channel_rfwd_bind_host(host))) != 0 ||
  	    (r = sshpkt_put_u32(ssh, port)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "send cancel");
  
  	fwd_perm_clear(perm); /* unregister */
  
  	return 0;
  }
  
  /*
   * Request cancellation of remote forwarding of Unix domain socket
   * path from local side.
   */
  static int
  channel_request_rforward_cancel_streamlocal(struct ssh *ssh, const char *path)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	int r;
  	u_int i;
  	struct permission *perm = NULL;
  
  	for (i = 0; i < pset->num_permitted_user; i++) {
  		perm = &pset->permitted_user[i];
  		if (open_listen_match_streamlocal(perm, path))
  			break;
  		perm = NULL;
  	}
  	if (perm == NULL) {
  		debug_f("requested forward not found");
  		return -1;
  	}
  	if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
  	    (r = sshpkt_put_cstring(ssh,
  	    "cancel-streamlocal-forward@openssh.com")) != 0 ||
  	    (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
  	    (r = sshpkt_put_cstring(ssh, path)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0)
  		fatal_fr(r, "send cancel");
  
  	fwd_perm_clear(perm); /* unregister */
  
  	return 0;
  }
  
  /*
   * Request cancellation of remote forwarding of a connection from local side.
   */
  int
  channel_request_rforward_cancel(struct ssh *ssh, struct Forward *fwd)
  {
  	if (fwd->listen_path != NULL) {
  		return channel_request_rforward_cancel_streamlocal(ssh,
  		    fwd->listen_path);
  	} else {
  		return channel_request_rforward_cancel_tcpip(ssh,
  		    fwd->listen_host,
  		    fwd->listen_port ? fwd->listen_port : fwd->allocated_port);
  	}
  }
  
  /*
   * Permits opening to any host/port if permitted_user[] is empty.  This is
   * usually called by the server, because the user could connect to any port
   * anyway, and the server has no way to know but to trust the client anyway.
   */
  void
  channel_permit_all(struct ssh *ssh, int where)
  {
  	struct permission_set *pset = permission_set_get(ssh, where);
  
  	if (pset->num_permitted_user == 0)
  		pset->all_permitted = 1;
  }
  
  /*
   * Permit the specified host/port for forwarding.
   */
  void
  channel_add_permission(struct ssh *ssh, int who, int where,
      char *host, int port)
  {
  	int local = where == FORWARD_LOCAL;
  	struct permission_set *pset = permission_set_get(ssh, where);
  
  	debug("allow %s forwarding to host %s port %d",
  	    fwd_ident(who, where), host, port);
  	/*
  	 * Remote forwards set listen_host/port, local forwards set
  	 * host/port_to_connect.
  	 */
  	permission_set_add(ssh, who, where,
  	    local ? host : NULL, local ? port : 0,
  	    local ? NULL : host, NULL, local ? 0 : port, NULL);
  	pset->all_permitted = 0;
  }
  
  /*
   * Administratively disable forwarding.
   */
  void
  channel_disable_admin(struct ssh *ssh, int where)
  {
  	channel_clear_permission(ssh, FORWARD_ADM, where);
  	permission_set_add(ssh, FORWARD_ADM, where,
  	    NULL, 0, NULL, NULL, 0, NULL);
  }
  
  /*
   * Clear a list of permitted opens.
   */
  void
  channel_clear_permission(struct ssh *ssh, int who, int where)
  {
  	struct permission **permp;
  	u_int i, *npermp;
  
  	permission_set_get_array(ssh, who, where, &permp, &npermp);
  	for (i = 0; i < *npermp; i++)
  		fwd_perm_clear((*permp) + i);
  	free(*permp);
  	*permp = NULL;
  	*npermp = 0;
  }
  
  /*
   * Update the listen port for a dynamic remote forward, after
   * the actual 'newport' has been allocated. If 'newport' < 0 is
   * passed then they entry will be invalidated.
   */
  void
  channel_update_permission(struct ssh *ssh, int idx, int newport)
  {
  	struct permission_set *pset = &ssh->chanctxt->local_perms;
  
  	if (idx < 0 || (u_int)idx >= pset->num_permitted_user) {
  		debug_f("index out of range: %d num_permitted_user %d",
  		    idx, pset->num_permitted_user);
  		return;
  	}
  	debug("%s allowed port %d for forwarding to host %s port %d",
  	    newport > 0 ? "Updating" : "Removing",
  	    newport,
  	    pset->permitted_user[idx].host_to_connect,
  	    pset->permitted_user[idx].port_to_connect);
  	if (newport <= 0)
  		fwd_perm_clear(&pset->permitted_user[idx]);
  	else {
  		pset->permitted_user[idx].listen_port =
  		    (ssh->compat & SSH_BUG_DYNAMIC_RPORT) ? 0 : newport;
  	}
  }
  
  /* Try to start non-blocking connect to next host in cctx list */
  static int
  connect_next(struct channel_connect *cctx)
  {
  	int sock, saved_errno;
  	struct sockaddr_un *sunaddr;
  	char ntop[NI_MAXHOST];
  	char strport[MAXIMUM(NI_MAXSERV, sizeof(sunaddr->sun_path))];
  
  	for (; cctx->ai; cctx->ai = cctx->ai->ai_next) {
  		switch (cctx->ai->ai_family) {
  		case AF_UNIX:
  			/* unix:pathname instead of host:port */
  			sunaddr = (struct sockaddr_un *)cctx->ai->ai_addr;
  			strlcpy(ntop, "unix", sizeof(ntop));
  			strlcpy(strport, sunaddr->sun_path, sizeof(strport));
  			break;
  		case AF_INET:
  		case AF_INET6:
  			if (getnameinfo(cctx->ai->ai_addr, cctx->ai->ai_addrlen,
  			    ntop, sizeof(ntop), strport, sizeof(strport),
  			    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
  				error_f("getnameinfo failed");
  				continue;
  			}
  			break;
  		default:
  			continue;
  		}
  		debug_f("start for host %.100s ([%.100s]:%s)",
  		    cctx->host, ntop, strport);
  		if ((sock = socket(cctx->ai->ai_family, cctx->ai->ai_socktype,
  		    cctx->ai->ai_protocol)) == -1) {
  			if (cctx->ai->ai_next == NULL)
  				error("socket: %.100s", strerror(errno));
  			else
  				verbose("socket: %.100s", strerror(errno));
  			continue;
  		}
  		if (set_nonblock(sock) == -1)
  			fatal_f("set_nonblock(%d)", sock);
  		if (connect(sock, cctx->ai->ai_addr,
  		    cctx->ai->ai_addrlen) == -1 && errno != EINPROGRESS) {
  			debug_f("host %.100s ([%.100s]:%s): %.100s",
  			    cctx->host, ntop, strport, strerror(errno));
  			saved_errno = errno;
  			close(sock);
  			errno = saved_errno;
  			continue;	/* fail -- try next */
  		}
  		if (cctx->ai->ai_family != AF_UNIX)
  			set_nodelay(sock);
  		debug_f("connect host %.100s ([%.100s]:%s) in progress, fd=%d",
  		    cctx->host, ntop, strport, sock);
  		cctx->ai = cctx->ai->ai_next;
  		return sock;
  	}
  	return -1;
  }
  
  static void
  channel_connect_ctx_free(struct channel_connect *cctx)
  {
  	free(cctx->host);
  	if (cctx->aitop) {
  		if (cctx->aitop->ai_family == AF_UNIX)
  			free(cctx->aitop);
  		else
  			freeaddrinfo(cctx->aitop);
  	}
  	memset(cctx, 0, sizeof(*cctx));
  }
  
  /*
   * Return connecting socket to remote host:port or local socket path,
   * passing back the failure reason if appropriate.
   */
  static int
  connect_to_helper(struct ssh *ssh, const char *name, int port, int socktype,
      char *ctype, char *rname, struct channel_connect *cctx,
      int *reason, const char **errmsg)
  {
  	struct addrinfo hints;
  	int gaierr;
  	int sock = -1;
  	char strport[NI_MAXSERV];
  
  	if (port == PORT_STREAMLOCAL) {
  		struct sockaddr_un *sunaddr;
  		struct addrinfo *ai;
  
  		if (strlen(name) > sizeof(sunaddr->sun_path)) {
  			error("%.100s: %.100s", name, strerror(ENAMETOOLONG));
  			return -1;
  		}
  
  		/*
  		 * Fake up a struct addrinfo for AF_UNIX connections.
  		 * channel_connect_ctx_free() must check ai_family
  		 * and use free() not freeaddrinfo() for AF_UNIX.
  		 */
  		ai = xcalloc(1, sizeof(*ai) + sizeof(*sunaddr));
  		ai->ai_addr = (struct sockaddr *)(ai + 1);
  		ai->ai_addrlen = sizeof(*sunaddr);
  		ai->ai_family = AF_UNIX;
  		ai->ai_socktype = socktype;
  		ai->ai_protocol = PF_UNSPEC;
  		sunaddr = (struct sockaddr_un *)ai->ai_addr;
  		sunaddr->sun_family = AF_UNIX;
  		strlcpy(sunaddr->sun_path, name, sizeof(sunaddr->sun_path));
  		cctx->aitop = ai;
  	} else {
  		memset(&hints, 0, sizeof(hints));
  		hints.ai_family = ssh->chanctxt->IPv4or6;
  		hints.ai_socktype = socktype;
  		snprintf(strport, sizeof strport, "%d", port);
  		if ((gaierr = getaddrinfo(name, strport, &hints, &cctx->aitop))
  		    != 0) {
  			if (errmsg != NULL)
  				*errmsg = ssh_gai_strerror(gaierr);
  			if (reason != NULL)
  				*reason = SSH2_OPEN_CONNECT_FAILED;
  			error("connect_to %.100s: unknown host (%s)", name,
  			    ssh_gai_strerror(gaierr));
  			return -1;
  		}
  	}
  
  	cctx->host = xstrdup(name);
  	cctx->port = port;
  	cctx->ai = cctx->aitop;
  
  	if ((sock = connect_next(cctx)) == -1) {
  		error("connect to %.100s port %d failed: %s",
  		    name, port, strerror(errno));
  		return -1;
  	}
  
  	return sock;
  }
  
  /* Return CONNECTING channel to remote host:port or local socket path */
  static Channel *
  connect_to(struct ssh *ssh, const char *host, int port,
      char *ctype, char *rname)
  {
  	struct channel_connect cctx;
  	Channel *c;
  	int sock;
  
  	memset(&cctx, 0, sizeof(cctx));
  	sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
  	    &cctx, NULL, NULL);
  	if (sock == -1) {
  		channel_connect_ctx_free(&cctx);
  		return NULL;
  	}
  	c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
  	    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  	c->host_port = port;
  	c->path = xstrdup(host);
  	c->connect_ctx = cctx;
  
  	return c;
  }
  
  /*
   * returns either the newly connected channel or the downstream channel
   * that needs to deal with this connection.
   */
  Channel *
  channel_connect_by_listen_address(struct ssh *ssh, const char *listen_host,
      u_short listen_port, char *ctype, char *rname)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	u_int i;
  	struct permission *perm;
  
  	for (i = 0; i < pset->num_permitted_user; i++) {
  		perm = &pset->permitted_user[i];
  		if (open_listen_match_tcpip(perm,
  		    listen_host, listen_port, 1)) {
  			if (perm->downstream)
  				return perm->downstream;
  			if (perm->port_to_connect == 0)
  				return rdynamic_connect_prepare(ssh,
  				    ctype, rname);
  			return connect_to(ssh,
  			    perm->host_to_connect, perm->port_to_connect,
  			    ctype, rname);
  		}
  	}
  	error("WARNING: Server requests forwarding for unknown listen_port %d",
  	    listen_port);
  	return NULL;
  }
  
  Channel *
  channel_connect_by_listen_path(struct ssh *ssh, const char *path,
      char *ctype, char *rname)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	u_int i;
  	struct permission *perm;
  
  	for (i = 0; i < pset->num_permitted_user; i++) {
  		perm = &pset->permitted_user[i];
  		if (open_listen_match_streamlocal(perm, path)) {
  			return connect_to(ssh,
  			    perm->host_to_connect, perm->port_to_connect,
  			    ctype, rname);
  		}
  	}
  	error("WARNING: Server requests forwarding for unknown path %.100s",
  	    path);
  	return NULL;
  }
  
  /* Check if connecting to that port is permitted and connect. */
  Channel *
  channel_connect_to_port(struct ssh *ssh, const char *host, u_short port,
      char *ctype, char *rname, int *reason, const char **errmsg)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	struct channel_connect cctx;
  	Channel *c;
  	u_int i, permit, permit_adm = 1;
  	int sock;
  	struct permission *perm;
  
  	permit = pset->all_permitted;
  	if (!permit) {
  		for (i = 0; i < pset->num_permitted_user; i++) {
  			perm = &pset->permitted_user[i];
  			if (open_match(perm, host, port)) {
  				permit = 1;
  				break;
  			}
  		}
  	}
  
  	if (pset->num_permitted_admin > 0) {
  		permit_adm = 0;
  		for (i = 0; i < pset->num_permitted_admin; i++) {
  			perm = &pset->permitted_admin[i];
  			if (open_match(perm, host, port)) {
  				permit_adm = 1;
  				break;
  			}
  		}
  	}
  
  	if (!permit || !permit_adm) {
  		logit("Received request from %.100s port %d to connect to "
  		    "host %.100s port %d, but the request was denied.",
  		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), host, port);
  		if (reason != NULL)
  			*reason = SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED;
  		return NULL;
  	}
  
  	memset(&cctx, 0, sizeof(cctx));
  	sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
  	    &cctx, reason, errmsg);
  	if (sock == -1) {
  		channel_connect_ctx_free(&cctx);
  		return NULL;
  	}
  
  	c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
  	    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  	c->host_port = port;
  	c->path = xstrdup(host);
  	c->connect_ctx = cctx;
  
  	return c;
  }
  
  /* Check if connecting to that path is permitted and connect. */
  Channel *
  channel_connect_to_path(struct ssh *ssh, const char *path,
      char *ctype, char *rname)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	u_int i, permit, permit_adm = 1;
  	struct permission *perm;
  
  	permit = pset->all_permitted;
  	if (!permit) {
  		for (i = 0; i < pset->num_permitted_user; i++) {
  			perm = &pset->permitted_user[i];
  			if (open_match(perm, path, PORT_STREAMLOCAL)) {
  				permit = 1;
  				break;
  			}
  		}
  	}
  
  	if (pset->num_permitted_admin > 0) {
  		permit_adm = 0;
  		for (i = 0; i < pset->num_permitted_admin; i++) {
  			perm = &pset->permitted_admin[i];
  			if (open_match(perm, path, PORT_STREAMLOCAL)) {
  				permit_adm = 1;
  				break;
  			}
  		}
  	}
  
  	if (!permit || !permit_adm) {
  		logit("Received request to connect to path %.100s, "
  		    "but the request was denied.", path);
  		return NULL;
  	}
  	return connect_to(ssh, path, PORT_STREAMLOCAL, ctype, rname);
  }
  
  void
  channel_send_window_changes(struct ssh *ssh)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct winsize ws;
  	int r;
  	u_int i;
  
  	for (i = 0; i < sc->channels_alloc; i++) {
  		if (sc->channels[i] == NULL || !sc->channels[i]->client_tty ||
  		    sc->channels[i]->type != SSH_CHANNEL_OPEN)
  			continue;
  		if (ioctl(sc->channels[i]->rfd, TIOCGWINSZ, &ws) == -1)
  			continue;
  		channel_request_start(ssh, i, "window-change", 0);
  		if ((r = sshpkt_put_u32(ssh, (u_int)ws.ws_col)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_row)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_xpixel)) != 0 ||
  		    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_ypixel)) != 0 ||
  		    (r = sshpkt_send(ssh)) != 0)
  			fatal_fr(r, "channel %u; send window-change", i);
  	}
  }
  
  /* Return RDYNAMIC_OPEN channel: channel allows SOCKS, but is not connected */
  static Channel *
  rdynamic_connect_prepare(struct ssh *ssh, char *ctype, char *rname)
  {
  	Channel *c;
  	int r;
  
  	c = channel_new(ssh, ctype, SSH_CHANNEL_RDYNAMIC_OPEN, -1, -1, -1,
  	    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  	c->host_port = 0;
  	c->path = NULL;
  
  	/*
  	 * We need to open the channel before we have a FD,
  	 * so that we can get SOCKS header from peer.
  	 */
  	if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0)
  		fatal_fr(r, "channel %i; confirm", c->self);
  	return c;
  }
  
  /* Return CONNECTING socket to remote host:port or local socket path */
  static int
  rdynamic_connect_finish(struct ssh *ssh, Channel *c)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	struct permission_set *pset = &sc->local_perms;
  	struct permission *perm;
  	struct channel_connect cctx;
  	u_int i, permit_adm = 1;
  	int sock;
  
  	if (pset->num_permitted_admin > 0) {
  		permit_adm = 0;
  		for (i = 0; i < pset->num_permitted_admin; i++) {
  			perm = &pset->permitted_admin[i];
  			if (open_match(perm, c->path, c->host_port)) {
  				permit_adm = 1;
  				break;
  			}
  		}
  	}
  	if (!permit_adm) {
  		debug_f("requested forward not permitted");
  		return -1;
  	}
  
  	memset(&cctx, 0, sizeof(cctx));
  	sock = connect_to_helper(ssh, c->path, c->host_port, SOCK_STREAM, NULL,
  	    NULL, &cctx, NULL, NULL);
  	if (sock == -1)
  		channel_connect_ctx_free(&cctx);
  	else {
  		/* similar to SSH_CHANNEL_CONNECTING but we've already sent the open */
  		c->type = SSH_CHANNEL_RDYNAMIC_FINISH;
  		c->connect_ctx = cctx;
  		channel_register_fds(ssh, c, sock, sock, -1, 0, 1, 0);
  	}
  	return sock;
  }
  
  /* -- X11 forwarding */
  
  /*
   * Creates an internet domain socket for listening for X11 connections.
   * Returns 0 and a suitable display number for the DISPLAY variable
   * stored in display_numberp , or -1 if an error occurs.
   */
  int
  x11_create_display_inet(struct ssh *ssh, int x11_display_offset,
      int x11_use_localhost, int single_connection,
      u_int *display_numberp, int **chanids)
  {
  	Channel *nc = NULL;
  	int display_number, sock, port;
  	struct addrinfo hints, *ai, *aitop;
  	char strport[NI_MAXSERV];
  	int gaierr, n, num_socks = 0, socks[NUM_SOCKS];
  
  	if (chanids == NULL || x11_display_offset < 0 ||
  	    x11_display_offset > UINT16_MAX - X11_BASE_PORT - MAX_DISPLAYS)
  		return -1;
  
  	for (display_number = x11_display_offset;
  	    display_number < x11_display_offset + MAX_DISPLAYS;
  	    display_number++) {
  		port = X11_BASE_PORT + display_number;
  		memset(&hints, 0, sizeof(hints));
  		hints.ai_family = ssh->chanctxt->IPv4or6;
  		hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
  		hints.ai_socktype = SOCK_STREAM;
  		snprintf(strport, sizeof strport, "%d", port);
  		if ((gaierr = getaddrinfo(NULL, strport,
  		    &hints, &aitop)) != 0) {
  			error("getaddrinfo: %.100s", ssh_gai_strerror(gaierr));
  			return -1;
  		}
  		for (ai = aitop; ai; ai = ai->ai_next) {
  			if (ai->ai_family != AF_INET &&
  			    ai->ai_family != AF_INET6)
  				continue;
  			sock = socket(ai->ai_family, ai->ai_socktype,
  			    ai->ai_protocol);
  			if (sock == -1) {
  				error("socket: %.100s", strerror(errno));
  				freeaddrinfo(aitop);
  				return -1;
  			}
  			set_reuseaddr(sock);
  			if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
  				debug2_f("bind port %d: %.100s", port,
  				    strerror(errno));
  				close(sock);
  				for (n = 0; n < num_socks; n++)
  					close(socks[n]);
  				num_socks = 0;
  				break;
  			}
  			socks[num_socks++] = sock;
  			if (num_socks == NUM_SOCKS)
  				break;
  		}
  		freeaddrinfo(aitop);
  		if (num_socks > 0)
  			break;
  	}
  	if (display_number >= x11_display_offset + MAX_DISPLAYS) {
  		error("Failed to allocate internet-domain X11 display socket.");
  		return -1;
  	}
  	/* Start listening for connections on the socket. */
  	for (n = 0; n < num_socks; n++) {
  		sock = socks[n];
  		if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
  			error("listen: %.100s", strerror(errno));
  			close(sock);
  			return -1;
  		}
  	}
  
  	/* Allocate a channel for each socket. */
  	*chanids = xcalloc(num_socks + 1, sizeof(**chanids));
  	for (n = 0; n < num_socks; n++) {
  		sock = socks[n];
  		nc = channel_new(ssh, "x11-listener",
  		    SSH_CHANNEL_X11_LISTENER, sock, sock, -1,
  		    CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
  		    0, "X11 inet listener", 1);
  		nc->single_connection = single_connection;
  		(*chanids)[n] = nc->self;
  	}
  	(*chanids)[n] = -1;
  
  	/* Return the display number for the DISPLAY environment variable. */
  	*display_numberp = display_number;
  	return 0;
  }
  
  static int
  connect_local_xsocket(u_int dnr)
  {
  	int sock;
  	struct sockaddr_un addr;
  
  	sock = socket(AF_UNIX, SOCK_STREAM, 0);
  	if (sock == -1)
  		error("socket: %.100s", strerror(errno));
  	memset(&addr, 0, sizeof(addr));
  	addr.sun_family = AF_UNIX;
  	snprintf(addr.sun_path, sizeof addr.sun_path, _PATH_UNIX_X, dnr);
  	if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == 0)
  		return sock;
  	close(sock);
  	error("connect %.100s: %.100s", addr.sun_path, strerror(errno));
  	return -1;
  }
  
  int
  x11_connect_display(struct ssh *ssh)
  {
  	u_int display_number;
  	const char *display;
  	char buf[1024], *cp;
  	struct addrinfo hints, *ai, *aitop;
  	char strport[NI_MAXSERV];
  	int gaierr, sock = 0;
  
  	/* Try to open a socket for the local X server. */
  	display = getenv("DISPLAY");
  	if (!display) {
  		error("DISPLAY not set.");
  		return -1;
  	}
  	/*
  	 * Now we decode the value of the DISPLAY variable and make a
  	 * connection to the real X server.
  	 */
  
  	/*
  	 * Check if it is a unix domain socket.  Unix domain displays are in
  	 * one of the following formats: unix:d[.s], :d[.s], ::d[.s]
  	 */
  	if (strncmp(display, "unix:", 5) == 0 ||
  	    display[0] == ':') {
  		/* Connect to the unix domain socket. */
  		if (sscanf(strrchr(display, ':') + 1, "%u",
  		    &display_number) != 1) {
  			error("Could not parse display number from DISPLAY: "
  			    "%.100s", display);
  			return -1;
  		}
  		/* Create a socket. */
  		sock = connect_local_xsocket(display_number);
  		if (sock < 0)
  			return -1;
  
  		/* OK, we now have a connection to the display. */
  		return sock;
  	}
  	/*
  	 * Connect to an inet socket.  The DISPLAY value is supposedly
  	 * hostname:d[.s], where hostname may also be numeric IP address.
  	 */
  	strlcpy(buf, display, sizeof(buf));
  	cp = strchr(buf, ':');
  	if (!cp) {
  		error("Could not find ':' in DISPLAY: %.100s", display);
  		return -1;
  	}
  	*cp = 0;
  	/*
  	 * buf now contains the host name.  But first we parse the
  	 * display number.
  	 */
  	if (sscanf(cp + 1, "%u", &display_number) != 1 ||
  	    display_number > UINT16_MAX - X11_BASE_PORT) {
  		error("Could not parse display number from DISPLAY: %.100s",
  		    display);
  		return -1;
  	}
  
  	/* Look up the host address */
  	memset(&hints, 0, sizeof(hints));
  	hints.ai_family = ssh->chanctxt->IPv4or6;
  	hints.ai_socktype = SOCK_STREAM;
  	snprintf(strport, sizeof strport, "%u", X11_BASE_PORT + display_number);
  	if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
  		error("%.100s: unknown host. (%s)", buf,
  		ssh_gai_strerror(gaierr));
  		return -1;
  	}
  	for (ai = aitop; ai; ai = ai->ai_next) {
  		/* Create a socket. */
  		sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
  		if (sock == -1) {
  			debug2("socket: %.100s", strerror(errno));
  			continue;
  		}
  		/* Connect it to the display. */
  		if (connect(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
  			debug2("connect %.100s port %u: %.100s", buf,
  			    X11_BASE_PORT + display_number, strerror(errno));
  			close(sock);
  			continue;
  		}
  		/* Success */
  		break;
  	}
  	freeaddrinfo(aitop);
  	if (!ai) {
  		error("connect %.100s port %u: %.100s", buf,
  		    X11_BASE_PORT + display_number, strerror(errno));
  		return -1;
  	}
  	set_nodelay(sock);
  	return sock;
  }
  
  /*
   * Requests forwarding of X11 connections, generates fake authentication
   * data, and enables authentication spoofing.
   * This should be called in the client only.
   */
  void
  x11_request_forwarding_with_spoofing(struct ssh *ssh, int client_session_id,
      const char *disp, const char *proto, const char *data, int want_reply)
  {
  	struct ssh_channels *sc = ssh->chanctxt;
  	u_int data_len = (u_int) strlen(data) / 2;
  	u_int i, value;
  	const char *cp;
  	char *new_data;
  	int r, screen_number;
  
  	if (sc->x11_saved_display == NULL)
  		sc->x11_saved_display = xstrdup(disp);
  	else if (strcmp(disp, sc->x11_saved_display) != 0) {
  		error("x11_request_forwarding_with_spoofing: different "
  		    "$DISPLAY already forwarded");
  		return;
  	}
  
  	cp = strchr(disp, ':');
  	if (cp)
  		cp = strchr(cp, '.');
  	if (cp)
  		screen_number = (u_int)strtonum(cp + 1, 0, 400, NULL);
  	else
  		screen_number = 0;
  
  	if (sc->x11_saved_proto == NULL) {
  		/* Save protocol name. */
  		sc->x11_saved_proto = xstrdup(proto);
  
  		/* Extract real authentication data. */
  		sc->x11_saved_data = xmalloc(data_len);
  		for (i = 0; i < data_len; i++) {
  			if (sscanf(data + 2 * i, "%2x", &value) != 1) {
  				fatal("x11_request_forwarding: bad "
  				    "authentication data: %.100s", data);
  			}
  			sc->x11_saved_data[i] = value;
  		}
  		sc->x11_saved_data_len = data_len;
  
  		/* Generate fake data of the same length. */
  		sc->x11_fake_data = xmalloc(data_len);
  		arc4random_buf(sc->x11_fake_data, data_len);
  		sc->x11_fake_data_len = data_len;
  	}
  
  	/* Convert the fake data into hex. */
  	new_data = tohex(sc->x11_fake_data, data_len);
  
  	/* Send the request packet. */
  	channel_request_start(ssh, client_session_id, "x11-req", want_reply);
  	if ((r = sshpkt_put_u8(ssh, 0)) != 0 || /* bool: single connection */
  	    (r = sshpkt_put_cstring(ssh, proto)) != 0 ||
  	    (r = sshpkt_put_cstring(ssh, new_data)) != 0 ||
  	    (r = sshpkt_put_u32(ssh, screen_number)) != 0 ||
  	    (r = sshpkt_send(ssh)) != 0 ||
  	    (r = ssh_packet_write_wait(ssh)) != 0)
  		fatal_fr(r, "send x11-req");
  	free(new_data);
  }
  
  /*
   * Returns whether an x11 channel was used recently (less than a second ago)
   */
  int
  x11_channel_used_recently(struct ssh *ssh) {
  	u_int i;
  	Channel *c;
  	time_t lastused = 0;
  
  	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
  		c = ssh->chanctxt->channels[i];
  		if (c == NULL || c->ctype == NULL || c->lastused == 0 ||
  		    strcmp(c->ctype, "x11-connection") != 0)
  			continue;
  		if (c->lastused > lastused)
  			lastused = c->lastused;
  	}
  	return lastused != 0 && monotime() <= lastused + 1;
  }