[FFmpeg-devel] [PATCH 2/2] avcodec/g2meet: Check for end of input in jpg_decode_block()

[Michael Niedermayer]

On Mon, Sep 09, 2019 at 11:04:32PM +0200, Tomas Härdin wrote:
> mån 2019-09-09 klockan 22:16 +0200 skrev Michael Niedermayer:
> > Fixes: Timeout (100sec -> 0.7sec)
> > Fixes: 8668/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_G2M_fuzzer-5174143888130048
> > 
> > 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/g2meet.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/libavcodec/g2meet.c b/libavcodec/g2meet.c
> > index 19e1c130ce..731d29a5d4 100644
> > --- a/libavcodec/g2meet.c
> > +++ b/libavcodec/g2meet.c
> > @@ -244,6 +244,9 @@ static int jpg_decode_block(JPGContext *c, GetBitContext *gb,
> >      const int is_chroma = !!plane;
> >      const uint8_t *qmat = is_chroma ? chroma_quant : luma_quant;
> >  
> > +    if (get_bits_left(gb) < 1)
> > +        return AVERROR_INVALIDDATA;
> > +
> >      c->bdsp.clear_block(block);
> >      dc = get_vlc2(gb, c->dc_vlc[is_chroma].table, 9, 3);
> 
> Why doesn't the VLC stuff have EOF handling? 

Because it doesnt need it in most of the cases and the get_vlc code
is quite speed critical in some codecs.
Also it would add a error return to cases that previously never
could receive an error. That would require callers to be changed
and check for this error in some cases


> There's bound to be a
> metric bajillion of cases like this strewn across the codebase..

if that was the case, the fuzzer would have likely found more cases.

thx

[...]
-- 
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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