[FFmpeg-devel] [PATCH 4/5] avcodec/hevc_mp4toannexb_bsf: check that nalu size doesnt overflow

[Michael Niedermayer]

On Fri, Dec 13, 2019 at 03:09:25PM -0500, Andriy Gelman wrote:
> On Fri, 13. Dec 18:51, Michael Niedermayer wrote:
> > On Thu, Dec 12, 2019 at 07:36:50PM -0500, Andriy Gelman wrote:
> > > On Fri, 13. Dec 01:28, Michael Niedermayer wrote:
> > > > Fixes: Out of array access
> > > > Fixes: 19299/clusterfuzz-testcase-minimized-ffmpeg_BSF_HEVC_MP4TOANNEXB_fuzzer-5169193398042624
> > > > 
> > > > 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/hevc_mp4toannexb_bsf.c | 3 +--
> > > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > > 
> > > > diff --git a/libavcodec/hevc_mp4toannexb_bsf.c b/libavcodec/hevc_mp4toannexb_bsf.c
> > > > index d0f1b94f0e..baa93628ed 100644
> > > > --- a/libavcodec/hevc_mp4toannexb_bsf.c
> > > > +++ b/libavcodec/hevc_mp4toannexb_bsf.c
> > > > @@ -152,8 +152,7 @@ static int hevc_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *out)
> > > >          extra_size    = add_extradata * ctx->par_out->extradata_size;
> > > >          got_irap     |= is_irap;
> > > >  
> > > > -        if (SIZE_MAX - nalu_size < 4 ||
> > > > -            SIZE_MAX - 4 - nalu_size < extra_size) {
> > > > +        if (FFMIN(INT_MAX, SIZE_MAX) < 4ULL + nalu_size + extra_size) {
> > > >              ret = AVERROR_INVALIDDATA;
> > > >              goto fail;
> > > >          }
> > > > -- 
> > > > 2.24.0
> > > 
> > > I already sent a patch for this:
> > > http://ffmpeg.org/pipermail/ffmpeg-devel/2019-December/253972.html
> > 
> > yes but it depends on "distant" code behaving in specific ways. I prefer
> > a single self contained check. Because its more robust to someone changing
> > that distant code.
> > So i would prefer to apply some "dumb" check. Do you agree ?
> 
> I agree it's more robust. I'll keep this in mind for future

will apply

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Never trust a computer, one day, it may think you are the virus. -- Compn
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