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stasis/app: don't lock an app before a call to send 

Calling 'app_send' eventually calls the app's message handler. It's possible
for a handler to obtain a lock on another object, and then need/want to lock
the app object. If the caller of 'app_send' locks the app object prior to
calling then there's a potential for a deadlock, if another thread calls
'app_send' without locking.

This patch makes it so 'app_send' is not called with the app object locked in
the section of code doing such.

ASTERISK-28423 #close

Change-Id: I6767c6d0933c7db1b984018966eefca4c0638a27
This commit is contained in:
Kevin Harwell 2020-01-27 12:01:15 -06:00
parent 313189aae2
commit cce2b0da95
1 changed files with 15 additions and 0 deletions
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15
res/stasis/app.c
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@ -1126,8 +1126,23 @@ void app_update(struct stasis_app *app, stasis_app_cb handler, void *data)
"timestamp", ast_json_timeval(ast_tvnow(), NULL),
"application", app->name);
if (msg) {
/*
* The app must be unlocked before calling 'send' since a handler may
* subsequently attempt to grab the app lock after first obtaining a
* lock for another object, thus causing a deadlock.
*/
ao2_unlock(app);
app_send(app, msg);
ao2_lock(app);
ast_json_unref(msg);
if (!app->handler) {
/*
* If the handler disappeared then the app was deactivated. In that
* case don't replace. Re-activation will reset the handler later.
*/
ao2_unlock(app);
return;
}
}
} else {
ast_verb(1, "Activating Stasis app '%s'\n", app->name);