[asterisk-bugs] [JIRA] (ASTERISK-21316) Segfault on ast_channel_tech(chan)->send_digit_begin

[Ashley Winters (JIRA)]

    [ https://issues.asterisk.org/jira/browse/ASTERISK-21316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=204790#comment-204790 ] 

Ashley Winters commented on ASTERISK-21316:
-------------------------------------------

It's a bridged call. We have a manager event listener which can trigger unbridge upon DTMF. It's like a dynamic features.conf for our multi-tenant IVR. So, sequence of events as best I can piece together:

1. Bridge channel A and B
2. DTMF # received on A
3. Simultaneously ChannelRedirect both A and B to dialplan locations, triggering unbridge
4. After {{ast_channel_bridge}} returns, the channels are not yet marked as ZOMBIE
6. Towards the end of {{ast_channel_bridge}}, it finally checks whether DTMF '#' should have triggered a feature, and if not forwards to the now-ZOMBIE channel
7. In between the NULL check of {{!ast_channel_tech(chan)->send_digit_begin}} and the segfault location, channel B is masqueraded on another thread
8. Segfault
                
> Segfault on ast_channel_tech(chan)->send_digit_begin
> ----------------------------------------------------
>
>                 Key: ASTERISK-21316
>                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-21316
>             Project: Asterisk
>          Issue Type: Bug
>      Security Level: None
>          Components: Core/Channels
>    Affects Versions: 11.2.1
>         Environment: CentOS 6.3
>            Reporter: Ashley Winters
>            Severity: Critical
>         Attachments: gdb-send_digit_begin-segfault.txt, unlocked-send_digit-race.patch
>
>
> Calling {{ast_channel_tech(chan)}} multiple times in a row while chan is unlocked is a race condition. I experienced a segfault when the tech changed to {{null_tech}} between the null check and the function-pointer dereference.

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