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parking: Use channel snapshot instead of channel. 

There exists a scenario where a thread can hold a lock on the
channels container while trying to lock a bridge. At the same
time another thread can hold the lock for said bridge while
attempting to retrieve a channel. This causes a deadlock.

This change fixes this scenario by retrieving a channel snapshot
instead of a channel, as information present in the snapshot
is all that is needed.

ASTERISK-28616

Change-Id: I68ceb1d62c7378addcd286e21be08a660a7cecf2
This commit is contained in:
Joshua Colp 2019-11-12 07:00:44 -04:00 committed by George Joseph
parent e3959a2fe1
commit e7320bbbf0
1 changed files with 14 additions and 15 deletions
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29
res/parking/parking_bridge.c
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@ -72,9 +72,9 @@ static void destroy_parked_user(void *obj)
}
/* Only call this on a parked user that hasn't had its parker_dial_string set already */
static int parked_user_set_parker_dial_string(struct parked_user *pu, struct ast_channel *parker)
static int parked_user_set_parker_dial_string(struct parked_user *pu, const char *parker_channel_name)
{
char *dial_string = ast_strdupa(ast_channel_name(parker));
char *dial_string = ast_strdupa(parker_channel_name);
ast_channel_name_to_dial_string(dial_string);
pu->parker_dial_string = ast_strdup(dial_string);
@ -93,7 +93,7 @@ static int parked_user_set_parker_dial_string(struct parked_user *pu, struct ast
*
* \param lot The parking lot we are assigning the user to
* \param parkee The channel being parked
* \param parker The channel performing the park operation (may be the same channel)
* \param parker_channel_name The name of the parker of this channel
* \param parker_dial_string Takes priority over parker for setting the parker dial string if included
* \param use_random_space if true, prioritize using a random parking space instead
* of ${PARKINGEXTEN} and/or automatic assignment from the parking lot
@ -106,7 +106,7 @@ static int parked_user_set_parker_dial_string(struct parked_user *pu, struct ast
*
* \note ao2_cleanup this reference when you are done using it or you'll cause leaks.
*/
static struct parked_user *generate_parked_user(struct parking_lot *lot, struct ast_channel *chan, struct ast_channel *parker, const char *parker_dial_string, int use_random_space, int time_limit)
static struct parked_user *generate_parked_user(struct parking_lot *lot, struct ast_channel *chan, const char *parker_channel_name, const char *parker_dial_string, int use_random_space, int time_limit)
{
struct parked_user *new_parked_user;
int preferred_space = -1; /* Initialize to use parking lot defaults */
@ -167,7 +167,7 @@ static struct parked_user *generate_parked_user(struct parking_lot *lot, struct
if (parker_dial_string) {
new_parked_user->parker_dial_string = ast_strdup(parker_dial_string);
} else {
if (!parker || parked_user_set_parker_dial_string(new_parked_user, parker)) {
if (ast_strlen_zero(parker_channel_name) || parked_user_set_parker_dial_string(new_parked_user, parker_channel_name)) {
ao2_ref(new_parked_user, -1);
ao2_unlock(lot);
return NULL;
@ -207,7 +207,8 @@ static int bridge_parking_push(struct ast_bridge_parking *self, struct ast_bridg
{
struct parked_user *pu;
const char *blind_transfer;
RAII_VAR(struct ast_channel *, parker, NULL, ao2_cleanup); /* XXX replace with ast_channel_cleanup when available */
struct ast_channel_snapshot *parker = NULL;
const char *parker_channel_name = NULL;
RAII_VAR(struct park_common_datastore *, park_datastore, NULL, park_common_datastore_free);
ast_bridge_base_v_table.push(&self->base, bridge_channel, swap);
@ -263,7 +264,7 @@ static int bridge_parking_push(struct ast_bridge_parking *self, struct ast_bridg
/* There was either a failure to apply the datastore when performing park common setup or else we had alloc failures while cloning. Abort. */
return -1;
}
parker = ast_channel_get_by_name(park_datastore->parker_uuid);
parker = ast_channel_snapshot_get_latest(park_datastore->parker_uuid);
/* If the parker and the parkee are the same channel pointer, then the channel entered using
* the park application. It's possible that the channel that transferred it is still alive (particularly
@ -272,18 +273,16 @@ static int bridge_parking_push(struct ast_bridge_parking *self, struct ast_bridg
blind_transfer = pbx_builtin_getvar_helper(bridge_channel->chan, "BLINDTRANSFER");
blind_transfer = ast_strdupa(S_OR(blind_transfer, ""));
ast_channel_unlock(bridge_channel->chan);
if ((!parker || parker == bridge_channel->chan)
if ((!parker || !strcmp(parker->name, ast_channel_name(bridge_channel->chan)))
&& !ast_strlen_zero(blind_transfer)) {
struct ast_channel *real_parker = ast_channel_get_by_name(blind_transfer);
if (real_parker) {
ao2_cleanup(parker);
parker = real_parker;
}
parker_channel_name = blind_transfer;
} else {
parker_channel_name = parker->name;
}
pu = generate_parked_user(self->lot, bridge_channel->chan, parker,
pu = generate_parked_user(self->lot, bridge_channel->chan, parker_channel_name,
park_datastore->parker_dial_string, park_datastore->randomize, park_datastore->time_limit);
ao2_cleanup(parker);
if (!pu) {
publish_parked_call_failure(bridge_channel->chan);
return -1;