[FFmpeg-devel] [PATCH v1] libavformat/hls: During operation, the user exits and interrupts, causing pls->segment to be released, resulting in a null pointer crash

[徐慧书]

It was found in the crash logs of online users, and it was also simulated
locally. In China, we have a very large number of users, and the hls
protocol is widely used, with hundreds of millions of views every day, and
every small problem becomes more obvious.


Andreas Rheinhardt <andreas.rheinhardt at gmail.com> 于2020年10月16日周五 下午9:32写道：

> javashu2012 at gmail.com:
> > From: bevis <javashu2012 at gmail.com>
> >
> > Signed-off-by: bevis <javashu2012 at gmail.com>
> > ---
> >  libavformat/hls.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavformat/hls.c b/libavformat/hls.c
> > index 72e28ab94f..0a522a4595 100644
> > --- a/libavformat/hls.c
> > +++ b/libavformat/hls.c
> > @@ -1979,17 +1979,18 @@ static int hls_read_header(AVFormatContext *s)
> >          pls->ctx->interrupt_callback = s->interrupt_callback;
> >          url = av_strdup(pls->segments[0]->url);
> >          ret = av_probe_input_buffer(&pls->pb, &in_fmt, url, NULL, 0, 0);
> > -        av_free(url);
> >          if (ret < 0) {
> >              /* Free the ctx - it isn't initialized properly at this
> point,
> >               * so avformat_close_input shouldn't be called. If
> >               * avformat_open_input fails below, it frees and zeros the
> >               * context, so it doesn't need any special treatment like
> this. */
> > -            av_log(s, AV_LOG_ERROR, "Error when loading first segment
> '%s'\n", pls->segments[0]->url);
> > +            av_log(s, AV_LOG_ERROR, "Error when loading first segment
> '%s'\n", url);
> >              avformat_free_context(pls->ctx);
> >              pls->ctx = NULL;
> > +            av_free(url);
> >              goto fail;
> >          }
> > +        av_free(url);
> >          pls->ctx->pb       = &pls->pb;
> >          pls->ctx->io_open  = nested_io_open;
> >          pls->ctx->flags   |= s->flags & ~AVFMT_FLAG_CUSTOM_IO;
> >
> The change itself seems fine to me (I wonder why this hasn't been
> noticed when writing/reviewing b5e39880fb), but your commit message is
> way too long: The first line should be a short description followed by a
> more detailed description lateron (in the next lines).
>
> How exactly did you find this?
>
> - Andreas
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