[Asterisk-code-review] autochan/mixmonitor/chanspy: Fix unsafe channel locking and ... (asterisk[13])
Richard Mudgett
asteriskteam at digium.com
Wed Mar 15 18:05:18 CDT 2017
Richard Mudgett has uploaded a new change for review. ( https://gerrit.asterisk.org/5219 )
Change subject: autochan/mixmonitor/chanspy: Fix unsafe channel locking and references.
......................................................................
autochan/mixmonitor/chanspy: Fix unsafe channel locking and references.
Dereferencing struct ast_autochan.chan without first calling
ast_autochan_channel_lock() is unsafe because the pointer could change at
any time due to a masquerade. Unfortunately, ast_autochan_channel_lock()
itself uses struct ast_autochan.chan unsafely and can result in a deadlock
if the original channel happens to get destroyed after a masquerade in
addition to the pointer getting changed.
The problem is more likely to happen with v11 and earlier because
masquerades are used to optimize out local channels on those versions.
However, it could still happen on newer versions if the channel is
executing a dialplan application when the channel is transferred or
redirected. In this situation a masquerade still must be used.
* Added a lock to struct ast_autochan to safely be able to use
ast_autochan.chan while trying to get the channel lock in
ast_autochan_channel_lock(). The locking order is the channel lock then
the autochan lock. Locking in the other direction requires deadlock
avoidance.
* Fix unsafe ast_autochan.chan usages in app_mixmonitor.c.
* Fix unsafe ast_autochan.chan usages in app_chanspy.c.
* app_chanspy.c: Removed unused autochan parameter from next_channel().
ASTERISK-26867
Change-Id: Id29dd22bc0f369b44e23ca423d2f3657187cc592
---
M apps/app_chanspy.c
M apps/app_mixmonitor.c
M include/asterisk/autochan.h
M main/autochan.c
4 files changed, 85 insertions(+), 34 deletions(-)
git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/19/5219/1
diff --git a/apps/app_chanspy.c b/apps/app_chanspy.c
index 19675fb..608eb6b 100644
--- a/apps/app_chanspy.c
+++ b/apps/app_chanspy.c
@@ -498,10 +498,15 @@
static int start_spying(struct ast_autochan *autochan, const char *spychan_name, struct ast_audiohook *audiohook)
{
+ int res;
+
+ ast_autochan_channel_lock(autochan);
ast_log(LOG_NOTICE, "Attaching %s to %s\n", spychan_name, ast_channel_name(autochan->chan));
ast_set_flag(audiohook, AST_AUDIOHOOK_TRIGGER_SYNC | AST_AUDIOHOOK_SMALL_QUEUE);
- return ast_audiohook_attach(autochan->chan, audiohook);
+ res = ast_audiohook_attach(autochan->chan, audiohook);
+ ast_autochan_channel_unlock(autochan);
+ return res;
}
static void change_spy_mode(const char digit, struct ast_flags *flags)
@@ -585,8 +590,14 @@
{
int retval = 0;
struct ast_autochan *internal_bridge_autochan;
- RAII_VAR(struct ast_channel *, bridged, ast_channel_bridge_peer(spyee_autochan->chan), ast_channel_cleanup);
+ struct ast_channel *spyee_chan;
+ RAII_VAR(struct ast_channel *, bridged, NULL, ast_channel_cleanup);
+ ast_autochan_channel_lock(spyee_autochan);
+ spyee_chan = ast_channel_ref(spyee_autochan->chan);
+ ast_autochan_channel_unlock(spyee_autochan);
+ bridged = ast_channel_bridge_peer(spyee_chan);
+ ast_channel_unref(spyee_chan);
if (!bridged) {
return -1;
}
@@ -598,12 +609,10 @@
return -1;
}
- ast_autochan_channel_lock(internal_bridge_autochan);
if (start_spying(internal_bridge_autochan, spyer_name, bridge_whisper_audiohook)) {
ast_log(LOG_WARNING, "Unable to attach barge audiohook on spyee '%s'. Barge mode disabled.\n", name);
retval = -1;
}
- ast_autochan_channel_unlock(internal_bridge_autochan);
*spyee_bridge_autochan = internal_bridge_autochan;
@@ -623,21 +632,25 @@
struct ast_autochan *spyee_bridge_autochan = NULL;
const char *spyer_name;
- if (ast_check_hangup(chan) || ast_check_hangup(spyee_autochan->chan) ||
- ast_test_flag(ast_channel_flags(spyee_autochan->chan), AST_FLAG_ZOMBIE)) {
+ ast_channel_lock(chan);
+ if (ast_check_hangup(chan)) {
+ ast_channel_unlock(chan);
return 0;
}
-
- ast_channel_lock(chan);
spyer_name = ast_strdupa(ast_channel_name(chan));
ast_channel_unlock(chan);
ast_autochan_channel_lock(spyee_autochan);
+ if (ast_check_hangup(spyee_autochan->chan)
+ || ast_test_flag(ast_channel_flags(spyee_autochan->chan), AST_FLAG_ZOMBIE)) {
+ ast_autochan_channel_unlock(spyee_autochan);
+ return 0;
+ }
name = ast_strdupa(ast_channel_name(spyee_autochan->chan));
- ast_autochan_channel_unlock(spyee_autochan);
ast_verb(2, "Spying on channel %s\n", name);
publish_chanspy_message(chan, spyee_autochan->chan, 1);
+ ast_autochan_channel_unlock(spyee_autochan);
memset(&csth, 0, sizeof(csth));
ast_copy_flags(&csth.flags, flags, AST_FLAGS_ALL);
@@ -829,7 +842,7 @@
}
static struct ast_autochan *next_channel(struct ast_channel_iterator *iter,
- struct ast_autochan *autochan, struct ast_channel *chan)
+ struct ast_channel *chan)
{
struct ast_channel *next;
struct ast_autochan *autochan_store;
@@ -966,11 +979,12 @@
waitms = 100;
num_spyed_upon = 0;
- for (autochan = next_channel(iter, autochan, chan);
- autochan;
- prev = autochan->chan, ast_autochan_destroy(autochan),
- autochan = next_autochan ? next_autochan :
- next_channel(iter, autochan, chan), next_autochan = NULL) {
+ for (autochan = next_channel(iter, chan);
+ autochan;
+ prev = autochan->chan,
+ ast_autochan_destroy(autochan),
+ autochan = next_autochan ?: next_channel(iter, chan),
+ next_autochan = NULL) {
int igrp = !mygroup;
int ienf = !myenforced;
@@ -984,13 +998,19 @@
break;
}
- if (ast_test_flag(flags, OPTION_BRIDGED) && !ast_channel_is_bridged(autochan->chan)) {
+ ast_autochan_channel_lock(autochan);
+ if (ast_test_flag(flags, OPTION_BRIDGED)
+ && !ast_channel_is_bridged(autochan->chan)) {
+ ast_autochan_channel_unlock(autochan);
continue;
}
- if (ast_check_hangup(autochan->chan) || ast_test_flag(ast_channel_flags(autochan->chan), AST_FLAG_SPYING)) {
+ if (ast_check_hangup(autochan->chan)
+ || ast_test_flag(ast_channel_flags(autochan->chan), AST_FLAG_SPYING)) {
+ ast_autochan_channel_unlock(autochan);
continue;
}
+ ast_autochan_channel_unlock(autochan);
if (mygroup) {
int num_groups = 0;
@@ -1008,11 +1028,13 @@
/* Before dahdi scan was part of chanspy, it would use the "GROUP" variable
* rather than "SPYGROUP", this check is done to preserve expected behavior */
+ ast_autochan_channel_lock(autochan);
if (ast_test_flag(flags, OPTION_DAHDI_SCAN)) {
group = pbx_builtin_getvar_helper(autochan->chan, "GROUP");
} else {
group = pbx_builtin_getvar_helper(autochan->chan, "SPYGROUP");
}
+ ast_autochan_channel_unlock(autochan);
if (!ast_strlen_zero(group)) {
ast_copy_string(dup_group, group, sizeof(dup_group));
@@ -1040,7 +1062,9 @@
snprintf(buffer, sizeof(buffer) - 1, ":%s:", myenforced);
+ ast_autochan_channel_lock(autochan);
ast_copy_string(ext + 1, ast_channel_name(autochan->chan), sizeof(ext) - 1);
+ ast_autochan_channel_unlock(autochan);
if ((end = strchr(ext, '-'))) {
*end++ = ':';
*end = '\0';
@@ -1062,7 +1086,9 @@
char *ptr, *s;
strcpy(peer_name, "spy-");
+ ast_autochan_channel_lock(autochan);
strncat(peer_name, ast_channel_name(autochan->chan), AST_NAME_STRLEN - 4 - 1);
+ ast_autochan_channel_unlock(autochan);
if ((ptr = strchr(peer_name, '/'))) {
*ptr++ = '\0';
for (s = peer_name; s < ptr; s++) {
@@ -1127,12 +1153,14 @@
next = ast_channel_unref(next);
} else {
/* stay on this channel, if it is still valid */
+ ast_autochan_channel_lock(autochan);
if (!ast_check_hangup(autochan->chan)) {
next_autochan = ast_autochan_setup(autochan->chan);
} else {
/* the channel is gone */
next_autochan = NULL;
}
+ ast_autochan_channel_unlock(autochan);
}
} else if (res == 0 && ast_test_flag(flags, OPTION_EXITONHANGUP)) {
ast_autochan_destroy(autochan);
diff --git a/apps/app_mixmonitor.c b/apps/app_mixmonitor.c
index 3515f4b..979bf2d 100644
--- a/apps/app_mixmonitor.c
+++ b/apps/app_mixmonitor.c
@@ -622,6 +622,16 @@
}
}
+static int mixmonitor_autochan_is_bridged(struct ast_autochan *autochan)
+{
+ int is_bridged;
+
+ ast_autochan_channel_lock(autochan);
+ is_bridged = ast_channel_is_bridged(autochan->chan);
+ ast_autochan_channel_unlock(autochan);
+ return is_bridged;
+}
+
static void *mixmonitor_thread(void *obj)
{
struct mixmonitor *mixmonitor = obj;
@@ -679,8 +689,7 @@
ast_audiohook_unlock(&mixmonitor->audiohook);
if (!ast_test_flag(mixmonitor, MUXFLAG_BRIDGED)
- || (mixmonitor->autochan->chan
- && ast_channel_is_bridged(mixmonitor->autochan->chan))) {
+ || mixmonitor_autochan_is_bridged(mixmonitor->autochan)) {
ast_mutex_lock(&mixmonitor->mixmonitor_ds->lock);
/* Write out the frame(s) */
@@ -729,11 +738,11 @@
ast_audiohook_unlock(&mixmonitor->audiohook);
- ast_autochan_channel_lock(mixmonitor->autochan);
if (ast_test_flag(mixmonitor, MUXFLAG_BEEP_STOP)) {
+ ast_autochan_channel_lock(mixmonitor->autochan);
ast_stream_and_wait(mixmonitor->autochan->chan, "beep", "");
+ ast_autochan_channel_unlock(mixmonitor->autochan);
}
- ast_autochan_channel_unlock(mixmonitor->autochan);
ast_autochan_destroy(mixmonitor->autochan);
@@ -805,11 +814,11 @@
return -1;
}
- ast_autochan_channel_lock(mixmonitor->autochan);
if (ast_test_flag(mixmonitor, MUXFLAG_BEEP_START)) {
+ ast_autochan_channel_lock(mixmonitor->autochan);
ast_stream_and_wait(mixmonitor->autochan->chan, "beep", "");
+ ast_autochan_channel_unlock(mixmonitor->autochan);
}
- ast_autochan_channel_unlock(mixmonitor->autochan);
mixmonitor_ds->samp_rate = 8000;
mixmonitor_ds->audiohook = &mixmonitor->audiohook;
diff --git a/include/asterisk/autochan.h b/include/asterisk/autochan.h
index 319c203..128377b 100644
--- a/include/asterisk/autochan.h
+++ b/include/asterisk/autochan.h
@@ -32,6 +32,7 @@
struct ast_autochan {
struct ast_channel *chan;
AST_LIST_ENTRY(ast_autochan) list;
+ ast_mutex_t lock;
};
/*!
@@ -61,19 +62,24 @@
* ast_autochan_channel_lock and ast_autochan_channel_unlock. An attempt to lock
* the autochan->chan directly may result in it being changed after you've
* retrieved the value of chan, but before you've had a chance to lock it.
- * First when chan is locked, the autochan structure is guaranteed to keep the
+ * While chan is locked, the autochan structure is guaranteed to keep the
* same channel.
*/
+/*!
+ * \brief Lock the autochan's channel lock.
+ *
+ * \note We must do deadlock avoidance because the channel lock is
+ * superior to the autochan lock in locking order.
+ */
#define ast_autochan_channel_lock(autochan) \
do { \
- struct ast_channel *autochan_chan = autochan->chan; \
- ast_channel_lock(autochan_chan); \
- if (autochan->chan == autochan_chan) { \
- break; \
+ ast_mutex_lock(&(autochan)->lock); \
+ while (ast_channel_trylock((autochan)->chan)) { \
+ DEADLOCK_AVOIDANCE(&(autochan)->lock); \
} \
- ast_channel_unlock(autochan_chan); \
- } while (1)
+ ast_mutex_unlock(&(autochan)->lock); \
+ } while (0)
#define ast_autochan_channel_unlock(autochan) \
ast_channel_unlock(autochan->chan)
diff --git a/main/autochan.c b/main/autochan.c
index c1e8b83..cf80d8f 100644
--- a/main/autochan.c
+++ b/main/autochan.c
@@ -48,14 +48,17 @@
if (!(autochan = ast_calloc(1, sizeof(*autochan)))) {
return NULL;
}
+ ast_mutex_init(&autochan->lock);
autochan->chan = ast_channel_ref(chan);
- ast_channel_lock(autochan->chan); /* autochan is still private, no need for ast_autochan_channel_lock() */
+ ast_debug(1, "Created autochan %p to hold channel %s (%p)\n",
+ autochan, ast_channel_name(chan), chan);
+
+ /* autochan is still private, no need for ast_autochan_channel_lock() */
+ ast_channel_lock(autochan->chan);
AST_LIST_INSERT_TAIL(ast_channel_autochans(autochan->chan), autochan, list);
ast_channel_unlock(autochan->chan);
-
- ast_debug(1, "Created autochan %p to hold channel %s (%p)\n", autochan, ast_channel_name(chan), chan);
return autochan;
}
@@ -77,6 +80,8 @@
autochan->chan = ast_channel_unref(autochan->chan);
+ ast_mutex_destroy(&autochan->lock);
+
ast_free(autochan);
}
@@ -86,13 +91,16 @@
AST_LIST_APPEND_LIST(ast_channel_autochans(new_chan), ast_channel_autochans(old_chan), list);
+ /* Deadlock avoidance is not needed since the channels are already locked. */
AST_LIST_TRAVERSE(ast_channel_autochans(new_chan), autochan, list) {
+ ast_mutex_lock(&autochan->lock);
if (autochan->chan == old_chan) {
- autochan->chan = ast_channel_unref(old_chan);
autochan->chan = ast_channel_ref(new_chan);
+ ast_channel_unref(old_chan);
ast_debug(1, "Autochan %p used to hold channel %s (%p) but now holds channel %s (%p)\n",
autochan, ast_channel_name(old_chan), old_chan, ast_channel_name(new_chan), new_chan);
}
+ ast_mutex_unlock(&autochan->lock);
}
}
--
To view, visit https://gerrit.asterisk.org/5219
To unsubscribe, visit https://gerrit.asterisk.org/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: Id29dd22bc0f369b44e23ca423d2f3657187cc592
Gerrit-PatchSet: 1
Gerrit-Project: asterisk
Gerrit-Branch: 13
Gerrit-Owner: Richard Mudgett <rmudgett at digium.com>
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