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

[Vignesh Venkat]

On Tue, Oct 3, 2023 at 3:56 PM Vignesh Venkat <vigneshv at google.com> wrote:
>
> On Fri, Sep 29, 2023 at 12:21 PM Michael Niedermayer
> <michael at 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 at 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 at 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.
>

The patch for disallowing multiple meta boxes is here:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20231003230423.951161-1-vigneshv@google.com/

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



-- 
Vignesh