Re: [FFmpeg-devel] [PATCH 3/5] avformat/mov: Better check for duplicate iloc

[Vignesh Venkat via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

On Fri, Sep 29, 2023 at 12:21 PM Michael Niedermayer
<michael@niedermayer.cc> wrote:
>
> On Tue, Apr 25, 2023 at 03:22:50PM -0700, Vignesh Venkatasubramanian wrote:
> > On Mon, Apr 17, 2023 at 4:18 PM Michael Niedermayer
> > <michael@niedermayer.cc> wrote:
> > >
> > > On Mon, Apr 17, 2023 at 12:36:26PM +0200, Anton Khirnov wrote:
> > > > Quoting Michael Niedermayer (2023-04-17 00:25:16)
> > > > > Fixes: memleak
> > > > > Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-6674082962997248
> > > > >
> > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > > > > ---
> > > > >  libavformat/mov.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/libavformat/mov.c b/libavformat/mov.c
> > > > > index 057fd872b10..6853bb324cf 100644
> > > > > --- a/libavformat/mov.c
> > > > > +++ b/libavformat/mov.c
> > > > > @@ -7777,7 +7777,7 @@ static int mov_read_iloc(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> > > > >          return 0;
> > > > >      }
> > > > >
> > > > > -    if (c->fc->nb_streams) {
> > > > > +    if (c->fc->nb_streams || c->avif_info) {
> > > >
> > > > This first condition is now redundant, is it not?
> > >
> > > Iam not sure
> >
> > I think the second condition alone should be enough here. Either way,
> > lgtm (if the current patch is more clearer for readers).
>
> Ill apply with teh first condition converted to an assert then
>
>

sounds good.

> >
> > > what exactly happens if a trak occurs before
> > >
> >
> > If a trak occurs before, then the condition in the line above should
> > take care of that case (!c->is_still_picture_avif). Because if a trak
> > was found, it will not be considered a still picture.
> >
> > > Iam also not sure what happens if multiple meta tags occur triggering
> > > the avif stream addition, i may be missing something but the code seems
> > > not to expect that
> > >
> >
> > Multiple meta tags are not allowed in the AVIF/HEIF specification.
>
> sure but what happens if the occur anyway, does the code handle that
> with no undefined behavior ?
>

yeah, the current code will treat each meta tag as a separate track
(AVStream). This should be disallowed, i will send a patch to error
out if more than one top-level meta box is seen.

> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> I have often repented speaking, but never of holding my tongue.
> -- Xenocrates
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-- 
Vignesh
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