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Bridging: Use a ref to bridge_channel's channel to prevent crash. 

There's a race condition with bridging where a bridge can be torn down
causing the bridge_channel's ast_channel to become NULL when it's still
needed. This particular case happened with attended transfers, but the
crash occurred when trying to publish a stasis message. Now, the
bridge_channel is locked, a ref to the ast_channel is obtained, and that
ref is passed down the chain.

Change-Id: Ic48715c0c041615d17d286790ae3e8c61bb28814
This commit is contained in:
Ben Ford 2020-08-31 11:14:20 -05:00 committed by Joshua Colp
parent bd0724c7ed
commit e7620d034a
3 changed files with 52 additions and 3 deletions
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14
include/asterisk/bridge_channel.h
View File

@ -193,6 +193,20 @@ struct ast_bridge_channel {
} stream_map;
};
/*!
* \brief Get a ref to the bridge_channel's ast_channel
*
* \param bridge_channel The bridge channel
*
* \note The returned channel NEEDS to be unref'd once you are done with it. In general, this
* function is best used when accessing the bridge_channel chan from outside of a bridging
* thread.
*
* \retval ref'd ast_channel on success
* \retval NULL otherwise
*/
struct ast_channel *ast_bridge_channel_get_chan(struct ast_bridge_channel *bridge_channel);
/*!
* \brief Try locking the bridge_channel.
*

21
main/bridge.c
View File

@ -1753,7 +1753,10 @@ int ast_bridge_join(struct ast_bridge *bridge,
ast_channel_lock(chan);
ast_channel_internal_bridge_channel_set(chan, NULL);
ast_channel_unlock(chan);
/* Due to a race condition, we lock the bridge channel here for ast_bridge_channel_get_chan */
ao2_lock(bridge_channel);
bridge_channel->chan = NULL;
ao2_unlock(bridge_channel);
/* If bridge_channel->swap is not NULL then the join failed. */
ao2_t_cleanup(bridge_channel->swap, "Bridge complete: join failed");
bridge_channel->swap = NULL;
@ -1822,7 +1825,10 @@ static void *bridge_channel_ind_thread(void *data)
ast_channel_lock(chan);
ast_channel_internal_bridge_channel_set(chan, NULL);
ast_channel_unlock(chan);
/* Lock here for ast_bridge_channel_get_chan */
ao2_lock(bridge_channel);
bridge_channel->chan = NULL;
ao2_unlock(bridge_channel);
/* If bridge_channel->swap is not NULL then the join failed. */
ao2_t_cleanup(bridge_channel->swap, "Bridge complete: Independent impart join failed");
bridge_channel->swap = NULL;
@ -1923,7 +1929,10 @@ static int bridge_impart_internal(struct ast_bridge *bridge,
ast_channel_lock(chan);
ast_channel_internal_bridge_channel_set(chan, NULL);
ast_channel_unlock(chan);
/* Lock here for ast_bridge_channel_get_chan */
ao2_lock(bridge_channel);
bridge_channel->chan = NULL;
ao2_unlock(bridge_channel);
ao2_t_cleanup(bridge_channel->swap, "Bridge complete: Impart failed");
bridge_channel->swap = NULL;
ast_bridge_features_destroy(bridge_channel->features);
@ -4771,14 +4780,22 @@ enum ast_transfer_result ast_bridge_transfer_attended(struct ast_channel *to_tra
if (to_transferee_bridge_channel) {
/* Take off hold if they are on hold. */
ast_bridge_channel_write_unhold(to_transferee_bridge_channel);
if (ast_bridge_channel_write_unhold(to_transferee_bridge_channel)) {
ast_log(LOG_ERROR, "Transferee channel disappeared during transfer!\n");
res = AST_BRIDGE_TRANSFER_FAIL;
goto end;
}
}
if (to_target_bridge_channel) {
const char *target_complete_sound;
/* Take off hold if they are on hold. */
ast_bridge_channel_write_unhold(to_target_bridge_channel);
if (ast_bridge_channel_write_unhold(to_target_bridge_channel)) {
ast_log(LOG_ERROR, "Target channel disappeared during transfer!\n");
res = AST_BRIDGE_TRANSFER_FAIL;
goto end;
}
/* Is there a courtesy sound to play to the target? */
ast_channel_lock(to_transfer_target);

20
main/bridge_channel.c
View File

@ -208,6 +208,17 @@ static void bridge_sync_signal(struct bridge_sync *sync_struct)
ast_sem_post(&sync_struct->sem);
}
struct ast_channel *ast_bridge_channel_get_chan(struct ast_bridge_channel *bridge_channel)
{
struct ast_channel *chan;
ao2_lock(bridge_channel);
chan = ao2_bump(bridge_channel->chan);
ao2_unlock(bridge_channel);
return chan;
}
void ast_bridge_channel_lock_bridge(struct ast_bridge_channel *bridge_channel)
{
struct ast_bridge *bridge;
@ -1177,7 +1188,14 @@ int ast_bridge_channel_write_hold(struct ast_bridge_channel *bridge_channel, con
int ast_bridge_channel_write_unhold(struct ast_bridge_channel *bridge_channel)
{
ast_channel_publish_cached_blob(bridge_channel->chan, ast_channel_unhold_type(), NULL);
struct ast_channel *chan = ast_bridge_channel_get_chan(bridge_channel);
if (!chan) {
return -1;
}
ast_channel_publish_cached_blob(chan, ast_channel_unhold_type(), NULL);
ao2_ref(chan, -1);
return ast_bridge_channel_write_control_data(bridge_channel, AST_CONTROL_UNHOLD, NULL, 0);
}