kc3-lang/gnulib/lib/chdir-safer.c

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• Hash : 24816be6
  Author :
  Date : 2010-09-01T13:45:53
  

  fcntl-h, etc.: prefer O_SEARCH to O_RDONLY when applicable
  
  POSIX 2008 specifies a new 'open' flag O_SEARCH, which can be used
  when one needs search access to a directory but not read access.
  On systems where it is available, it works in some cases where
  O_RDONLY does not, namely on directories that are searchable but
  not readable, and which need only to be searchable.  If O_SEARCH
  is not available, fall back to the traditional method of using
  O_RDONLY.
  
  * lib/fcntl.in.h (O_SEARCH): #define to O_RDONLY if not defined.
  * lib/chdir-long.c (cdb_advance_fd): Use O_SEARCH, not O_RDONLY,
  when opening a directory that needs only to be searchable.
  * lib/chdir-safer.c (chdir_no_follow): Likewise.
  * lib/fts.c (diropen, fts_open, fd_ring_check): Likewise.
  * lib/openat-proc.c (openat_proc_name): Likewise.
  * lib/openat.c (openat_needs_fchdir): Likewise.
  * lib/save-cwd.c (save_cwd): Likewise.
  * lib/savewd.c (savewd_save, savewd_chdir): Likewise.
  

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• lib/chdir-safer.c

• /* much like chdir(2), but safer
  
     Copyright (C) 2005-2006, 2008-2010 Free Software Foundation, Inc.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 3 of the License, or
     (at your option) any later version.
  
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  
  /* written by Jim Meyering */
  
  #include <config.h>
  
  #include "chdir-safer.h"
  
  #include <stdbool.h>
  #include <fcntl.h>
  #include <errno.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include "same-inode.h"
  
  #ifndef HAVE_READLINK
  # define HAVE_READLINK 0
  #endif
  
  /* Like chdir, but fail if DIR is a symbolic link to a directory (or
     similar funny business).  This avoids a minor race condition
     between when a directory is created or statted and when the process
     chdirs into it.
  
     On older systems lacking full support for O_SEARCH, this function
     can also fail if DIR is not readable.  */
  int
  chdir_no_follow (char const *dir)
  {
    int result = 0;
    int saved_errno;
    int fd = open (dir,
                   O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK);
    if (fd < 0)
      return -1;
  
    /* If open follows symlinks, lstat DIR and fstat FD to ensure that
       they are the same file; if they are different files, set errno to
       ELOOP (the same value that open uses for symlinks with
       O_NOFOLLOW) so the caller can report a failure.
       Skip this check if HAVE_READLINK == 0, which should be the case
       on any system that lacks symlink support.  */
    if (HAVE_READLINK && ! HAVE_WORKING_O_NOFOLLOW)
      {
        struct stat sb1;
        result = lstat (dir, &sb1);
        if (result == 0)
          {
            struct stat sb2;
            result = fstat (fd, &sb2);
            if (result == 0 && ! SAME_INODE (sb1, sb2))
              {
                errno = ELOOP;
                result = -1;
              }
          }
      }
  
    if (result == 0)
      result = fchdir (fd);
  
    saved_errno = errno;
    close (fd);
    errno = saved_errno;
    return result;
  }
  

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