Yaron Nachum wrote:
Hello Asterisk users and developers,
The last few weeks we had several crashes on live asterisks running
versions  12.2.0rc1 / 12.6.1 with PJPROJECT versions 2.1.0 / 2.2.1. We
opened a ticket - ASTERISK-24471.

After investigating the issue I can say that the scenario is a CANCEL
being received while handling ANSWER and before generating the 200OK
response.

Looking at the core file we see that the problem is in
- pjsip/src/pjsip/sip_transaction.c line 3158 :
         PJ_ASSERT_RETURN(event->type == PJSIP_EVENT_TX_MSG &&
event->body.tx_msg.tdata == tsx->last_tx,
                          PJ_EINVALIDOP);

After investigating further I came to a conclusion that the second
expression fails (marked with yellow), and that causes the Asterisk to
crash.

I have already removed the expression and logged whenever this
expression fails. It seems to work fine. Since the change it the
happened several times, the application didn't crash and going over the
debug it seems that the call was handled fine.

Can anyone tell what is the purpose of this expression? Any explanation
why this expression fails in the above scenario?

PJSIP is written with assertions in various places which check various conditions to make sure that things are as expected. In the above scenario what's happening is that the CANCEL is coming in and changing the transaction so when the answer is sent (which occurs after handling the CANCEL) it is not in the expected state and it asserts. It's safe to do as you've done since the operation will do nothing, but that's not a viable fix to push upstream as it's a result of an implementation detail with chan_pjsip. The fix will occur in chan_pjsip once the issue is handled.

--
Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org

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