[FFmpeg-devel] [PATCH v2] avformat/imfdec: check track valid before use it

[Pierre-Anthony Lemieux]

On Fri, Aug 26, 2022 at 9:01 AM Andreas Rheinhardt
<andreas.rheinhardt at outlook.com> wrote:
>
> Pierre-Anthony Lemieux:
> > On Fri, Aug 26, 2022 at 1:37 AM Andreas Rheinhardt
> > <andreas.rheinhardt at outlook.com> wrote:
> >>
> >> Steven Liu:
> >>> fix CID: 1512414
> >>> And return AVERROR_INVALIDDATA when get_next_track_with_minimum_timestamp
> >>> incorrect in imf_read_packet;
> >>>
> >>> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
> >>> ---
> >>>  libavformat/imfdec.c | 7 +++++--
> >>>  1 file changed, 5 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/libavformat/imfdec.c b/libavformat/imfdec.c
> >>> index 5bbe7a53f8..08f342bc1a 100644
> >>> --- a/libavformat/imfdec.c
> >>> +++ b/libavformat/imfdec.c
> >>> @@ -697,8 +697,9 @@ static IMFVirtualTrackPlaybackCtx *get_next_track_with_minimum_timestamp(AVForma
> >>>          }
> >>>      }
> >>>
> >>> -    av_log(s, AV_LOG_DEBUG, "Found next track to read: %d (timestamp: %lf / %lf)\n",
> >>> -           track->index, av_q2d(track->current_timestamp), av_q2d(minimum_timestamp));
> >>> +    if (track)
> >>> +        av_log(s, AV_LOG_DEBUG, "Found next track to read: %d (timestamp: %lf / %lf)\n",
> >>> +               track->index, av_q2d(track->current_timestamp), av_q2d(minimum_timestamp));
> >>
> >> Coverity actually complained about track being uninitialized, which this
> >> patch does not address. And the reason it does this is that it doesn't
> >> understand the algorithm: track will always be initialized in the first
> >> iteration of the loop.
> >
> > Is it possible to tell coverity that  c->track_count > 0 is a
> > pre-condition, or should we modify the loop/algorithm?
> >
>
> The typical way to do this is to add an av_assert1 or av_assert2;
> but this must only be done if it is indeed ensured that the assert will
> not be triggered.
>
> >> (If there is a first iteration of the loop -- is
> >> this actually guaranteed? A file without tracks seems to be pretty useless.)
> >
> > imfdec currently assumes that (a) imf_read_packet() is not called if
> > there are no streams/tracks and (b) a track will always be found.
> >
> > (b) will be true for a conformant IMF Composition, but I am not sure
> > it can always be true for a malformed one.
> >
>
> Can't we make it true by adding the relevant checks to read_header?

Yes.

>
> > I think imf_read_packet() can probably be hardened. Perhaps do this as
> > a patch separately from addressing the coverity issue?
> >
> >> FYI: In Coverity's analysis there are loop iterations, but it just
> >> assumed that track is not initialized in the loop (which boils down to
> >> saying that it presumed the tracks' current_timestamp to be invalid
> >> (denominator 0). I hope this can't happen.
> >> (There is btw another issue: The initialization of minimum_timestamp
> >> presumes that int are 32bit which need not be true.)
> >
> > INT32_MAX -> INT_MAX should fix this right?
> >
>
> Yes.
>
> >>
> >>>      return track;
> >>>  }
> >>>
> >>> @@ -760,6 +761,8 @@ static int imf_read_packet(AVFormatContext *s, AVPacket *pkt)
> >>>      AVRational next_timestamp;
> >>>
> >>>      track = get_next_track_with_minimum_timestamp(s);
> >>> +    if (!track)
> >>> +        return AVERROR_INVALIDDATA;
> >>>
> >>>      ret = get_resource_context_for_timestamp(s, track, &resource);
> >>>      if (ret)
> >>
> >> _______________________________________________
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> >>
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