[FFmpeg-devel] [PATCH] avcodec/argo: Check for end of input in decode_alcd()

[Paul B Mahol]

On Fri, Jul 30, 2021 at 12:16 AM Andreas Rheinhardt <
andreas.rheinhardt at outlook.com> wrote:

> Andreas Rheinhardt:
> > Michael Niedermayer:
> >> Fixes: reading over the end
> >> Fixes:
> 36346/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ARGO_fuzzer-5366943107383296
> >>
> >> 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/argo.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/libavcodec/argo.c b/libavcodec/argo.c
> >> index bbdb6ae15f..79a44d2583 100644
> >> --- a/libavcodec/argo.c
> >> +++ b/libavcodec/argo.c
> >> @@ -116,6 +116,8 @@ static int decode_alcd(AVCodecContext *avctx,
> AVFrame *frame)
> >>              int index;
> >>
> >>              if (count == 0) {
> >> +                if (bytestream2_get_bytes_left(gb) < 1)
> >> +                    return AVERROR_INVALIDDATA;
> >>                  codes = bytestream2_get_byteu(&sb);
> >>                  count = 8;
> >>              }
> >>
> > Does the following also fix the issue?
> >
> > diff --git a/libavcodec/argo.c b/libavcodec/argo.c
> >
> > index bbdb6ae15f..602c042568 100644
> >
> > --- a/libavcodec/argo.c
> >
> > +++ b/libavcodec/argo.c
> >
> > @@ -102,13 +102,14 @@ static int decode_alcd(AVCodecContext *avctx,
> > AVFrame *frame)
> >
> >      uint8_t *dst = frame->data[0];
> >
> >      uint8_t codes = 0;
> >
> >      int count = 0;
> >
> > +    int num_codes = ((frame->width + 1) / 2 * (frame->height + 1) / 2 +
> > 7) >> 3;
> >
> >
> >
> > -    if (bytestream2_get_bytes_left(gb) < 1024 + (((frame->width / 2) *
> > (frame->height / 2) + 7) >> 3))
> >
> > +    if (bytestream2_get_bytes_left(gb) < 1024 + num_codes)
> >
> >          return AVERROR_INVALIDDATA;
> >
> >
> >
> >      bytestream2_skipu(gb, 1024);
> >
> >      sb = *gb;
> >
> > -    bytestream2_skipu(gb, ((frame->width / 2) * (frame->height / 2) +
> > 7) >> 3);
> >
> > +    bytestream2_skipu(gb, num_codes);
> >
> >
> >
> >      for (int y = 0; y < frame->height; y += 2) {
> >
> >          for (int x = 0; x < frame->width; x += 2) {
> >
> As can be seen from the above patch, my guess is that odd dimensions are
> the cause (because num_codes as above is the number of codes that is
> actually read); but my patch would not only change the criterion for
> when to error out, but also how much to skip (i.e. where the real data
> begins) and this makes me wonder whether we should not error out in this
> case (and ask for a sample).
>

I like Andreas solution much more, anway original video files are having
even dimensions,
so there is nothing to worry.


> - Andreas
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