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

[Martin Storsjö]

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.

// Martin