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bridge.c: Fixed race condition during attended transfer

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During an attended transfer a thread is started that handles imparting the
bridge channel. From the start of the thread to when the bridge channel is
ready exists a gap that can potentially cause problems (for instance, the
channel being swapped is hung up before the replacement channel enters the
bridge thus stopping the transfer). This patch adds a condition that waits
for the impart thread to get to a point of acceptable readiness before
allowing the initiating thread to continue.

ASTERISK-24782
Reported by: John Bigelow

Change-Id: I08fe33a2560da924e676df55b181e46fca604577
This commit is contained in:
Kevin Harwell
2015-07-08 14:56:10 -05:00
parent 7ff1ac8797
commit 97ee0ee6c6
4 changed files with 109 additions and 9 deletions
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51
main/bridge.c
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@@ -1551,7 +1551,7 @@ int ast_bridge_join(struct ast_bridge *bridge,
}
if (!res) {
res = bridge_channel_internal_join(bridge_channel);
res = bridge_channel_internal_join(bridge_channel, NULL);
}
/* Cleanup all the data in the bridge channel after it leaves the bridge. */
@@ -1581,13 +1581,14 @@ join_exit:;
/*! \brief Thread responsible for imparted bridged channels to be departed */
static void *bridge_channel_depart_thread(void *data)
{
struct ast_bridge_channel *bridge_channel = data;
struct bridge_channel_internal_cond *cond = data;
struct ast_bridge_channel *bridge_channel = cond->bridge_channel;
if (bridge_channel->callid) {
ast_callid_threadassoc_add(bridge_channel->callid);
}
bridge_channel_internal_join(bridge_channel);
bridge_channel_internal_join(bridge_channel, cond);
/*
* cleanup
@@ -1608,14 +1609,15 @@ static void *bridge_channel_depart_thread(void *data)
/*! \brief Thread responsible for independent imparted bridged channels */
static void *bridge_channel_ind_thread(void *data)
{
struct ast_bridge_channel *bridge_channel = data;
struct bridge_channel_internal_cond *cond = data;
struct ast_bridge_channel *bridge_channel = cond->bridge_channel;
struct ast_channel *chan;
if (bridge_channel->callid) {
ast_callid_threadassoc_add(bridge_channel->callid);
}
bridge_channel_internal_join(bridge_channel);
bridge_channel_internal_join(bridge_channel, cond);
chan = bridge_channel->chan;
/* cleanup */
@@ -1699,13 +1701,27 @@ int ast_bridge_impart(struct ast_bridge *bridge,
/* Actually create the thread that will handle the channel */
if (!res) {
struct bridge_channel_internal_cond cond = {
.done = 0,
.bridge_channel = bridge_channel
};
ast_mutex_init(&cond.lock);
ast_cond_init(&cond.cond, NULL);
if ((flags & AST_BRIDGE_IMPART_CHAN_MASK) == AST_BRIDGE_IMPART_CHAN_INDEPENDENT) {
res = ast_pthread_create_detached(&bridge_channel->thread, NULL,
bridge_channel_ind_thread, bridge_channel);
bridge_channel_ind_thread, &cond);
} else {
res = ast_pthread_create(&bridge_channel->thread, NULL,
bridge_channel_depart_thread, bridge_channel);
bridge_channel_depart_thread, &cond);
}
if (!res) {
bridge_channel_internal_wait(&cond);
}
ast_cond_destroy(&cond.cond);
ast_mutex_destroy(&cond.lock);
}
if (res) {
@@ -3955,6 +3971,15 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
struct ast_channel *chan2, struct ast_bridge *bridge1, struct ast_bridge *bridge2,
struct ast_attended_transfer_message *transfer_msg)
{
#define BRIDGE_LOCK_ONE_OR_BOTH(b1, b2) \
do { \
if (b2) { \
ast_bridge_lock_both(b1, b2); \
} else { \
ast_bridge_lock(b1); \
} \
} while (0)
static const char *dest = "_attended@transfer/m";
struct ast_channel *local_chan;
int cause;
@@ -3985,8 +4010,18 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
return AST_BRIDGE_TRANSFER_FAIL;
}
/*
* Since bridges need to be unlocked before entering ast_bridge_impart and
* core_local may call into it then the bridges need to be unlocked here.
*/
ast_bridge_unlock(bridge1);
if (bridge2) {
ast_bridge_unlock(bridge2);
}
if (ast_call(local_chan, dest, 0)) {
ast_hangup(local_chan);
BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
return AST_BRIDGE_TRANSFER_FAIL;
}
@@ -3996,8 +4031,10 @@ static enum ast_transfer_result attended_transfer_bridge(struct ast_channel *cha
AST_BRIDGE_IMPART_CHAN_INDEPENDENT)) {
ast_hangup(local_chan);
ao2_cleanup(local_chan);
BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
return AST_BRIDGE_TRANSFER_FAIL;
}
BRIDGE_LOCK_ONE_OR_BOTH(bridge1, bridge2);
if (bridge2) {
RAII_VAR(struct ast_channel *, local_chan2, NULL, ao2_cleanup);