[asterisk-bugs] [JIRA] (ASTERISK-23287) res_pjsip_refer: Crash during attended transfer when attended->transferer_second channel is NULL

[Kinsey Moore (JIRA)]

    [ https://issues.asterisk.org/jira/browse/ASTERISK-23287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=215603#comment-215603 ] 

Kinsey Moore commented on ASTERISK-23287:
-----------------------------------------

Doing a little debugging and looking at the resulting backtraces, this is not quite as simple as tossing an extra ref in there for that channel. Something appears to be consuming a ref that shouldn't be, so it's time to enable REF_DEBUG.
                
> res_pjsip_refer: Crash during attended transfer when attended->transferer_second channel is NULL
> ------------------------------------------------------------------------------------------------
>
>                 Key: ASTERISK-23287
>                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-23287
>             Project: Asterisk
>          Issue Type: Bug
>          Components: Resources/res_pjsip_refer
>    Affects Versions: 12.0.0
>            Reporter: Matt Jordan
>         Attachments: backtrace_5214.txt, full.txt
>
>
> Note that this was caught by the Asterisk Test Suite during the ARI attended transfer event test. Backtrace is attached.
> {noformat}
> #0  0x000000000053da03 in ast_channel_name (chan=0x0) at channel_internal_api.c:464
> 464	DEFINE_STRINGFIELD_GETTER_FOR(name);
> #0  0x000000000053da03 in ast_channel_name (chan=0x0) at channel_internal_api.c:464
> No locals.
> #1  0x00007f05e9000f08 in refer_attended (data=0x7f060c0523c8) at res_pjsip_refer.c:424
>         attended = 0x7f060c0523c8
>         response = 0
>         __PRETTY_FUNCTION__ = "refer_attended"
> {noformat}
> This occurs because some channel is NULL that we weren't expecting. Looking at line 424:
> {noformat}
> 	ast_debug(3, "Performing a REFER attended transfer - Transferer #1: %s Transferer #2: %s\n",
> 		ast_channel_name(attended->transferer_chan), ast_channel_name(attended->transferer_second->channel));
> {noformat}
> So we have either {{attended->transferer_chan}}, or {{attended->transferer_second->channel}}.
> When we make the {{attended}} structure, we are ref bumping the {{ast_sip_session}} objects, but only the {{attended->transferer_chan}} channel is ref bumped:
> {noformat}
> 	struct refer_attended *attended = ao2_alloc(sizeof(*attended), refer_attended_destroy);
> 	if (!attended) {
> 		return NULL;
> 	}
> 	ao2_ref(transferer, +1);
> 	attended->transferer = transferer;
> 	ast_channel_ref(transferer->channel);
> 	attended->transferer_chan = transferer->channel;
> 	ao2_ref(transferer_second, +1);
> 	attended->transferer_second = transferer_second;
> 	if (progress) {
> 		ao2_ref(progress, +1);
> 		attended->progress = progress;
> 	}
> {noformat}
> The most likely culprit for this failing is the attended->transferer_second channel getting nuked out while we serialize the task.

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