[FFmpeg-devel] [PATCH 2/3] avcodec/iff: Check ham vs bpp

[Michael Niedermayer]

On Sun, Jun 23, 2019 at 10:45:56AM +0200, Michael Niedermayer wrote:
> On Sun, Jun 23, 2019 at 06:33:02PM +1000, Peter Ross wrote:
> > On Sun, Jun 23, 2019 at 12:30:54AM +0200, Michael Niedermayer wrote:
> > > This checks the ham value much stricter and avoids hitting cases which cannot be reached
> > > with data from the libavformat demuxer.
> > > 
> > > Fixes: out of array access
> > > Fixes: 15320/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5080476840099840
> > > Fixes: 15423/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_IFF_ILBM_fuzzer-5630765833912320
> > > 
> > > 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/iff.c | 15 ++++++++++++---
> > >  1 file changed, 12 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/libavcodec/iff.c b/libavcodec/iff.c
> > > index b43bd507b3..b065bbe598 100644
> > > --- a/libavcodec/iff.c
> > > +++ b/libavcodec/iff.c
> > > @@ -280,6 +280,18 @@ static int extract_header(AVCodecContext *const avctx,
> > >          for (i = 0; i < 16; i++)
> > >              s->tvdc[i] = bytestream_get_be16(&buf);
> > >  
> > > +        if (s->ham) {
> > > +            if (s->bpp > 8) {
> > > +                av_log(avctx, AV_LOG_ERROR, "Invalid number of hold bits for HAM: %u\n", s->ham);
> > > +                s->ham = 0;
> > > +                return AVERROR_INVALIDDATA;
> > > +            } if (s->ham != (s->bpp > 6 ? 6 : 4)) {
> > > +                av_log(avctx, AV_LOG_ERROR, "Invalid number of hold bits for HAM: %u, BPP: %u\n", s->ham, s->bpp);
> > > +                s->ham = 0;
> > > +                return AVERROR_INVALIDDATA;
> > > +            }
> > > +        }
> > 
> > i am curious why we need to reset ham = 0? otherwise patch okay.
> 
> That was just so as not to leave an invalid value in the context. It is
> very likely not needed, I will remove it.

will apply without the ham = 0


[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In a rich man's house there is no place to spit but his face.
-- Diogenes of Sinope
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