[FFmpeg-devel] [PATCH] avcodec/hevcdec: do not let updated extradata corrupt state

[Michael Niedermayer]

On Wed, Jul 05, 2017 at 09:56:10AM +0200, wm4 wrote:
> On Tue,  4 Jul 2017 22:33:52 +0200
> Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
> > Fixes: out of array access
> > Fixes: 2451/clusterfuzz-testcase-minimized-4781613957251072
> > 
> > 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/hevcdec.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> > index cc8ac82164..55f51211c3 100644
> > --- a/libavcodec/hevcdec.c
> > +++ b/libavcodec/hevcdec.c
> > @@ -3057,7 +3057,7 @@ static int verify_md5(HEVCContext *s, AVFrame *frame)
> >      return 0;
> >  }
> >  
> > -static int hevc_decode_extradata(HEVCContext *s, uint8_t *buf, int length)
> > +static int hevc_decode_extradata(HEVCContext *s, uint8_t *buf, int length, int first)
> >  {
> >      int ret, i;
> >  
> > @@ -3069,7 +3069,7 @@ static int hevc_decode_extradata(HEVCContext *s, uint8_t *buf, int length)
> >  
> >      /* export stream parameters from the first SPS */
> >      for (i = 0; i < FF_ARRAY_ELEMS(s->ps.sps_list); i++) {
> > -        if (s->ps.sps_list[i]) {
> > +        if (first && s->ps.sps_list[i]) {
> >              const HEVCSPS *sps = (const HEVCSPS*)s->ps.sps_list[i]->data;
> >              export_stream_params(s->avctx, &s->ps, sps);
> >              break;
> > @@ -3099,7 +3099,7 @@ static int hevc_decode_frame(AVCodecContext *avctx, void *data, int *got_output,
> >      new_extradata = av_packet_get_side_data(avpkt, AV_PKT_DATA_NEW_EXTRADATA,
> >                                              &new_extradata_size);
> >      if (new_extradata && new_extradata_size > 0) {
> > -        ret = hevc_decode_extradata(s, new_extradata, new_extradata_size);
> > +        ret = hevc_decode_extradata(s, new_extradata, new_extradata_size, 0);
> >          if (ret < 0)
> >              return ret;
> >      }
> > @@ -3387,7 +3387,7 @@ static av_cold int hevc_decode_init(AVCodecContext *avctx)
> >          s->threads_number = 1;
> >  
> >      if (avctx->extradata_size > 0 && avctx->extradata) {
> > -        ret = hevc_decode_extradata(s, avctx->extradata, avctx->extradata_size);
> > +        ret = hevc_decode_extradata(s, avctx->extradata, avctx->extradata_size, 1);
> >          if (ret < 0) {
> >              hevc_decode_free(avctx);
> >              return ret;
> 
> Couldn't that have done in a less confusing way? What the heck does
> "first" even mean? (Also you have to look up what that means on the
> caller site.)
> 
> Can you explain this?

first means "Preceding all others of a series or kind;" https://en.wiktionary.org/wiki/first
in the context of hevc_decode_extradata(), a function decoding extradata
that signifies the first of a series of extradata.

No question it can be done differently, everything can be done
differently.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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