[FFmpeg-devel] [PATCH] avcodec/vp3: Check that there will be sufficient input for the coded fragments in unpack_superblocks()

[Michael Niedermayer]

On Sat, May 05, 2018 at 09:14:52PM +0200, wm4 wrote:
> On Sat,  5 May 2018 21:10:06 +0200
> Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
> > Fixes: Timeout
> > Fixes: 6292/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP3_fuzzer-4871218218926080
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/vp3.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
> > index 1d83753314..fcc19a627b 100644
> > --- a/libavcodec/vp3.c
> > +++ b/libavcodec/vp3.c
> > @@ -543,7 +543,11 @@ static int unpack_superblocks(Vp3DecodeContext *s, GetBitContext *gb)
> >                                           : s->y_superblock_count);
> >          int num_coded_frags = 0;
> >  
> > -        for (i = sb_start; i < sb_end && get_bits_left(gb) > 0; i++) {
> > +        for (i = sb_start; i < sb_end; i++) {
> > +            if (get_bits_left(gb) < ((s->total_num_coded_frags + num_coded_frags) >> 2)) {
> > +                av_log(s->avctx, AV_LOG_ERROR, "Insufficient input data for coded fragments\n");
> > +                return AVERROR_INVALIDDATA;
> > +            }
> >              /* iterate through all 16 fragments in a superblock */
> >              for (j = 0; j < 16; j++) {
> >                  /* if the fragment is in bounds, check its coding status */
> 
> The log message is pointless bloat.

All error returns of this function print a log message.

Thanks

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
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