On Fri, Mar 10, 2017 at 04:01:36PM +0100, wm4 wrote: > On Fri, 10 Mar 2017 15:24:52 +0100 > Michael Niedermayer <mich...@niedermayer.cc> wrote: > > > Fixes: 755/clusterfuzz-testcase-5369072516595712 > > > > See: [FFmpeg-devel] [PATCH 1/2] avcodec/h264_direct: Fix runtime error: > > signed integer overflow: 2147483647 - -14133 cannot be represented in type > > 'int' > > > > Found-by: continuous fuzzing process > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > --- > > libavcodec/h264_direct.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/libavcodec/h264_direct.c b/libavcodec/h264_direct.c > > index cbb84665b3..66e54479d1 100644 > > --- a/libavcodec/h264_direct.c > > +++ b/libavcodec/h264_direct.c > > @@ -39,7 +39,12 @@ static int get_scale_factor(H264SliceContext *sl, > > int poc, int poc1, int i) > > { > > int poc0 = sl->ref_list[0][i].poc; > > - int td = av_clip_int8(poc1 - poc0); > > + int64_t pocdiff = poc1 - (int64_t)poc0; > > + int td = av_clip_int8(pocdiff); > > + > > + if (pocdiff != (int)pocdiff) > > + avpriv_request_sample(sl->h264->avctx, "pocdiff overflow\n"); > > + > > if (td == 0 || sl->ref_list[0][i].parent->long_ref) { > > return 256; > > } else { > > Hard to image that these poc values aren't bounded by something else, > but I don't know.
> > Also the previous patch didn't have this request_sample call, which > inflates this whole thing by 5 lines of code. yes thats why i suggested it initially. SUINT allows overflow detection simply by #define CHECKED 1 and running under ubsan otherwise an excplicit check is needed to detect such occurances [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Breaking DRM is a little like attempting to break through a door even though the window is wide open and the only thing in the house is a bunch of things you dont want and which you would get tomorrow for free anyway
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