[FFmpeg-devel] [PATCH] rtmpproto: Avoid rare crashes in the fail: codepath in rtmp_open

[Martin Storsjö]

On Tue, 28 Jan 2025, Martin Storsjö wrote:

> On Thu, 23 Jan 2025, Martin Storsjö wrote:
>
>> When running the cleanup in rtmp_close on failures in rtmp_open,
>> we can in rare cases end up using rt->playpath, assuming that it
>> is still set.
>> 
>> The crash could happen if we hit the fail codepath in rtmp_open
>> while publishing (rt->is_input == 0) with rt->state set to
>> a value > STATE_FCPUBLISH.
>> 
>> This would normally not happen while publishing; either we have
>> an error (and rt->state <= STATE_FCPUBLISH) or we reach
>> rt->state = STATE_PUBLISHING, and then we also return successfully
>> from rtmp_open.
>> 
>> The unexpected combination of states could happen if the server
>> responds with e.g. "NetStream.Play.Stop" while expecting
>> "NetStream.Publish.Start"; this sets rt->state to STATE_STOPPED,
>> which also fulfills the condition "> STATE_FCPUBLISH".
>> 
>> We don't need to free the rt->playpath/tcurl/flashver strings here;
>> they're handled via AVOption, and thus are freed automatically when
>> the protocol instance is freed (that's why they aren't freed
>> manually within the rtmp_close function either).
>> 
>> We also don't need to free the AVDictionary with options; it's
>> owned by the caller.
>> 
>> A smaller fix would be to just call rtmp_close before freeing
>> the strings and dictionary, but as we don't need to free them
>> at all, let's remove that redundant code.
>> ---
>> libavformat/rtmpproto.c | 4 ----
>> 1 file changed, 4 deletions(-)
>> 
>> diff --git a/libavformat/rtmpproto.c b/libavformat/rtmpproto.c
>> index a34020b092..4095ae9421 100644
>> --- a/libavformat/rtmpproto.c
>> +++ b/libavformat/rtmpproto.c
>> @@ -2925,10 +2925,6 @@ reconnect:
>>     return 0;
>> 
>> fail:
>> -    av_freep(&rt->playpath);
>> -    av_freep(&rt->tcurl);
>> -    av_freep(&rt->flashver);
>> -    av_dict_free(opts);
>>     rtmp_close(s);
>>     return ret;
>> }
>> -- 
>> 2.39.5 (Apple Git-154)
>
> Will push soon.

Pushed.

// Martin