Branch
Hash :
628f39bb
Author :
Date :
2024-08-12T10:00:44
ws: fix potential NULL pointer dereference
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#include "event2/event-config.h"
#include "evconfig-private.h"
#include "event2/buffer.h"
#include "event2/bufferevent.h"
#include "event2/event.h"
#include "event2/http.h"
#include "event2/ws.h"
#include "util-internal.h"
#include "mm-internal.h"
#include "sha1.h"
#include "event2/bufferevent.h"
#include "sys/queue.h"
#include "http-internal.h"
#include "bufferevent-internal.h"
#include <assert.h>
#include <inttypes.h>
#include <string.h>
#include <stdbool.h>
#ifndef _WIN32
#include <sys/socket.h>
#include <sys/stat.h>
#else /* _WIN32 */
#include <winsock2.h>
#include <ws2tcpip.h>
#endif /* _WIN32 */
#ifdef EVENT__HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef EVENT__HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef EVENT__HAVE_NETINET_IN6_H
#include <netinet/in6.h>
#endif
#define WS_UUID "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
/*
* We limit the size of received WS frames to 10 MiB,
* as a DoS prevention measure.
*/
static const size_t WS_MAX_RECV_FRAME_SZ = 10485760;
struct evws_connection {
TAILQ_ENTRY(evws_connection) next;
struct bufferevent *bufev;
ws_on_msg_cb cb;
void *cb_arg;
ws_on_close_cb cbclose;
void *cbclose_arg;
/* for server connections, the http server they are connected with */
struct evhttp *http_server;
struct evbuffer *incomplete_frames;
bool closed;
};
enum WebSocketFrameType {
ERROR_FRAME = 0xFF,
INCOMPLETE_DATA = 0xFE,
CLOSING_FRAME = 0x8,
INCOMPLETE_FRAME = 0x81,
TEXT_FRAME = 0x1,
BINARY_FRAME = 0x2,
PING_FRAME = 0x9,
PONG_FRAME = 0xA
};
static void evws_send(struct evws_connection *evws,
enum WebSocketFrameType frame_type, const char *packet_str, size_t str_len);
/*
* Clean up a WebSockets connection object
*/
void
evws_connection_free(struct evws_connection *evws)
{
/* notify interested parties that this connection is going down */
if (evws->cbclose != NULL)
(*evws->cbclose)(evws, evws->cbclose_arg);
if (evws->http_server != NULL) {
struct evhttp *http = evws->http_server;
TAILQ_REMOVE(&http->ws_sessions, evws, next);
http->connection_cnt--;
}
if (evws->bufev != NULL) {
bufferevent_free(evws->bufev);
}
if (evws->incomplete_frames != NULL) {
evbuffer_free(evws->incomplete_frames);
}
mm_free(evws);
}
static const char basis_64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static int
Base64encode(char *encoded, const char *string, int len)
{
int i;
char *p;
p = encoded;
for (i = 0; i < len - 2; i += 3) {
*p++ = basis_64[(string[i] >> 2) & 0x3F];
*p++ = basis_64[((string[i] & 0x3) << 4) |
((int)(string[i + 1] & 0xF0) >> 4)];
*p++ = basis_64[((string[i + 1] & 0xF) << 2) |
((int)(string[i + 2] & 0xC0) >> 6)];
*p++ = basis_64[string[i + 2] & 0x3F];
}
if (i < len) {
*p++ = basis_64[(string[i] >> 2) & 0x3F];
if (i == (len - 1)) {
*p++ = basis_64[((string[i] & 0x3) << 4)];
*p++ = '=';
} else {
*p++ = basis_64[((string[i] & 0x3) << 4) |
((int)(string[i + 1] & 0xF0) >> 4)];
*p++ = basis_64[((string[i + 1] & 0xF) << 2)];
}
*p++ = '=';
}
*p++ = '\0';
return p - encoded;
}
static char *
ws_gen_accept_key(const char *ws_key, char out[32])
{
char buf[1024];
char digest[20];
snprintf(buf, sizeof(buf), "%s" WS_UUID, ws_key);
builtin_SHA1(digest, buf, strlen(buf));
Base64encode(out, digest, sizeof(digest));
return out;
}
static void
close_after_write_cb(struct bufferevent *bev, void *ctx)
{
if (evbuffer_get_length(bufferevent_get_output(bev)) == 0) {
evws_connection_free(ctx);
}
}
static void
close_event_cb(struct bufferevent *bev, short what, void *ctx)
{
evws_connection_free(ctx);
}
void
evws_close(struct evws_connection *evws, uint16_t reason)
{
uint8_t fr[4] = {0x8 | 0x80, 2, 0};
struct evbuffer *output;
uint16_t *u16;
if (evws->closed)
return;
evws->closed = true;
u16 = (uint16_t *)&fr[2];
*u16 = htons((int16_t)reason);
output = bufferevent_get_output(evws->bufev);
evbuffer_add(output, fr, 4);
/* wait for close frame writing complete and close connection */
bufferevent_setcb(
evws->bufev, NULL, close_after_write_cb, close_event_cb, evws);
}
static void
evws_force_disconnect_(struct evws_connection *evws)
{
evws_close(evws, WS_CR_NONE);
}
/* parse base frame according to
* https://www.rfc-editor.org/rfc/rfc6455#section-5.2
*/
static enum WebSocketFrameType
get_ws_frame(unsigned char *in_buffer, size_t buf_len,
unsigned char **payload_ptr, size_t *out_len)
{
unsigned char opcode;
unsigned char fin;
unsigned char masked;
size_t payload_len;
size_t pos;
int length_field;
if (buf_len < 2) {
return INCOMPLETE_DATA;
}
opcode = in_buffer[0] & 0x0F;
fin = (in_buffer[0] >> 7) & 0x01;
masked = (in_buffer[1] >> 7) & 0x01;
payload_len = 0;
pos = 2;
length_field = in_buffer[1] & (~0x80);
if (length_field <= 125) {
payload_len = length_field;
} else if (length_field == 126) { /* msglen is 16bit */
uint16_t tmp16;
if (buf_len < 4)
return INCOMPLETE_DATA;
memcpy(&tmp16, in_buffer + pos, 2);
payload_len = ntohs(tmp16);
pos += 2;
} else if (length_field == 127) { /* msglen is 64bit */
int i;
uint64_t tmp64 = 0;
if (buf_len < 10)
return INCOMPLETE_DATA;
/* swap bytes from big endian to host byte order */
for (i = 56; i >= 0; i -= 8) {
tmp64 |= (uint64_t)in_buffer[pos++] << i;
}
if (tmp64 > WS_MAX_RECV_FRAME_SZ) {
/* Implementation limitation, we support up to 10 MiB
* length, as a DoS prevention measure.
*/
event_warn("%s: frame length %" PRIu64 " exceeds %" PRIu64 "\n",
__func__, tmp64, (uint64_t)WS_MAX_RECV_FRAME_SZ);
/* Calling code needs these values; do the best we can here.
* Caller will close the connection anyway.
*/
*payload_ptr = in_buffer + pos;
*out_len = 0;
return ERROR_FRAME;
}
payload_len = (size_t)tmp64;
}
if (buf_len < payload_len + pos + (masked ? 4u : 0u)) {
return INCOMPLETE_DATA;
}
/* According to RFC it seems that unmasked data should be prohibited
* but we support it for nonconformant clients
*/
if (masked) {
unsigned char *c, *mask;
size_t i;
mask = in_buffer + pos; /* first 4 bytes are mask bytes */
pos += 4;
/* unmask data */
c = in_buffer + pos;
for (i = 0; i < payload_len; i++) {
c[i] = c[i] ^ mask[i % 4u];
}
}
*payload_ptr = in_buffer + pos;
*out_len = payload_len;
/* are reserved for further frames */
if ((opcode >= 3 && opcode <= 7) || (opcode >= 0xb))
return ERROR_FRAME;
if (opcode <= 0x3 && !fin) {
return INCOMPLETE_FRAME;
}
return opcode;
}
static void
ws_evhttp_read_cb(struct bufferevent *bufev, void *arg)
{
struct evws_connection *evws = arg;
unsigned char *payload;
enum WebSocketFrameType type;
size_t msg_len, in_len, header_sz;
struct evbuffer *input = bufferevent_get_input(evws->bufev);
bufferevent_incref_and_lock_(evws->bufev);
while ((in_len = evbuffer_get_length(input))) {
unsigned char *data = evbuffer_pullup(input, in_len);
if (data == NULL) {
goto bailout;
}
type = get_ws_frame(data, in_len, &payload, &msg_len);
if (type == INCOMPLETE_DATA) {
/* incomplete data received, wait for next chunk */
goto bailout;
}
header_sz = payload - data;
evbuffer_drain(input, header_sz);
data = evbuffer_pullup(input, -1);
switch (type) {
case TEXT_FRAME:
case BINARY_FRAME:
if (evws->incomplete_frames != NULL) {
/* we already have incomplete frames in internal buffer
* and need to concatenate them with final one */
evbuffer_add(evws->incomplete_frames, data, msg_len);
data = evbuffer_pullup(evws->incomplete_frames, -1);
evws->cb(evws, type, data,
evbuffer_get_length(evws->incomplete_frames), evws->cb_arg);
evbuffer_free(evws->incomplete_frames);
evws->incomplete_frames = NULL;
} else {
evws->cb(evws, type, data, msg_len, evws->cb_arg);
}
break;
case INCOMPLETE_FRAME:
/* we received full frame until get fin and need to
* postpone callback until all data arrives */
if (evws->incomplete_frames == NULL) {
evws->incomplete_frames = evbuffer_new();
}
evbuffer_remove_buffer(input, evws->incomplete_frames, msg_len);
continue;
case CLOSING_FRAME:
case ERROR_FRAME:
evws_force_disconnect_(evws);
break;
case PING_FRAME:
case PONG_FRAME:
/* ping or pong frame */
break;
default:
event_warn("%s: unexpected frame type %d\n", __func__, type);
evws_force_disconnect_(evws);
}
evbuffer_drain(input, msg_len);
}
bailout:
bufferevent_decref_and_unlock_(evws->bufev);
}
static void
ws_evhttp_error_cb(struct bufferevent *bufev, short what, void *arg)
{
/* when client just disappears after connection (wscat closed by Cmd+Q) */
if (what & BEV_EVENT_EOF) {
close_after_write_cb(bufev, arg);
}
}
struct evws_connection *
evws_new_session(
struct evhttp_request *req, ws_on_msg_cb cb, void *arg, int options)
{
struct evws_connection *evws = NULL;
struct evkeyvalq *in_hdrs;
const char *upgrade, *connection, *ws_key, *ws_protocol;
struct evkeyvalq *out_hdrs;
struct evhttp_connection *evcon;
in_hdrs = evhttp_request_get_input_headers(req);
upgrade = evhttp_find_header(in_hdrs, "Upgrade");
if (upgrade == NULL || evutil_ascii_strcasecmp(upgrade, "websocket"))
goto error;
connection = evhttp_find_header(in_hdrs, "Connection");
if (connection == NULL || evutil_ascii_strcasestr(connection, "Upgrade") == NULL)
goto error;
ws_key = evhttp_find_header(in_hdrs, "Sec-WebSocket-Key");
if (ws_key == NULL)
goto error;
out_hdrs = evhttp_request_get_output_headers(req);
evhttp_add_header(out_hdrs, "Upgrade", "websocket");
evhttp_add_header(out_hdrs, "Connection", "Upgrade");
evhttp_add_header(out_hdrs, "Sec-WebSocket-Accept",
ws_gen_accept_key(ws_key, (char[32]){0}));
ws_protocol = evhttp_find_header(in_hdrs, "Sec-WebSocket-Protocol");
if (ws_protocol != NULL)
evhttp_add_header(out_hdrs, "Sec-WebSocket-Protocol", ws_protocol);
if ((evws = mm_calloc(1, sizeof(struct evws_connection))) == NULL) {
event_warn("%s: calloc failed", __func__);
goto error;
}
evws->cb = cb;
evws->cb_arg = arg;
evcon = evhttp_request_get_connection(req);
evws->http_server = evcon->http_server;
evws->bufev = evhttp_start_ws_(req);
if (evws->bufev == NULL) {
goto error;
}
if (options & BEV_OPT_THREADSAFE) {
if (bufferevent_enable_locking_(evws->bufev, NULL) < 0)
goto error;
}
bufferevent_setcb(
evws->bufev, ws_evhttp_read_cb, NULL, ws_evhttp_error_cb, evws);
TAILQ_INSERT_TAIL(&evws->http_server->ws_sessions, evws, next);
evws->http_server->connection_cnt++;
return evws;
error:
if (evws)
evws_connection_free(evws);
evhttp_send_reply(req, HTTP_BADREQUEST, NULL, NULL);
return NULL;
}
static void
make_ws_frame(struct evbuffer *output, enum WebSocketFrameType frame_type,
unsigned char *msg, size_t len)
{
size_t pos = 0;
unsigned char header[16] = {0};
header[pos++] = (unsigned char)frame_type | 0x80; /* fin */
if (len <= 125) {
header[pos++] = len;
} else if (len <= 65535) {
header[pos++] = 126; /* 16 bit length */
header[pos++] = (len >> 8) & 0xFF; /* rightmost first */
header[pos++] = len & 0xFF;
} else { /* >2^16-1 */
int i;
const uint64_t tmp64 = len;
header[pos++] = 127; /* 64 bit length */
/* swap bytes from host byte order to big endian */
for (i = 56; i >= 0; i -= 8) {
header[pos++] = tmp64 >> i & 0xFFu;
}
}
evbuffer_add(output, header, pos);
evbuffer_add(output, msg, len);
}
static void
evws_send(struct evws_connection *evws, enum WebSocketFrameType frame_type,
const char *packet_str, size_t str_len)
{
struct evbuffer *output;
bufferevent_lock(evws->bufev);
output = bufferevent_get_output(evws->bufev);
make_ws_frame(output, frame_type, (unsigned char *)packet_str, str_len);
bufferevent_unlock(evws->bufev);
}
void
evws_send_text(struct evws_connection *evws, const char *packet_str)
{
evws_send(evws, TEXT_FRAME, packet_str, strlen(packet_str));
}
void
evws_send_binary(
struct evws_connection *evws, const char *packet_data, size_t packet_len)
{
evws_send(evws, BINARY_FRAME, packet_data, packet_len);
}
void
evws_connection_set_closecb(
struct evws_connection *evws, ws_on_close_cb cb, void *cbarg)
{
evws->cbclose = cb;
evws->cbclose_arg = cbarg;
}
struct bufferevent *
evws_connection_get_bufferevent(struct evws_connection *evws)
{
return evws->bufev;
}