[FFmpeg-devel] [PATCH 1/4] avcodec/prosumer: Check for bytestream eof in decompress()

[Michael Niedermayer]

On Wed, Oct 31, 2018 at 12:06:28PM +0100, Hendrik Leppkes wrote:
> On Wed, Oct 31, 2018 at 12:03 PM Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> >
> > Fixes: Infinite loop
> > Fixes: 10685/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PROSUMER_fuzzer-5652236881887232
> >
> > 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/prosumer.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/prosumer.c b/libavcodec/prosumer.c
> > index 6e98677b55..2fd9880ee1 100644
> > --- a/libavcodec/prosumer.c
> > +++ b/libavcodec/prosumer.c
> > @@ -57,7 +57,7 @@ static int decompress(GetByteContext *gb, int size, PutByteContext *pb, const ui
> >      b = lut[2 * idx];
> >
> >      while (1) {
> > -        if (bytestream2_get_bytes_left_p(pb) <= 0)
> > +        if (bytestream2_get_bytes_left_p(pb) <= 0 || bytestream2_get_eof(pb))
> >              return 0;
> >          if (((b & 0xFF00u) != 0x8000u) || (b & 0xFFu)) {
> >              if ((b & 0xFF00u) != 0x8000u) {
> 
> Why does bytestream2_get_bytes_left_p not return <= 0 at eof, where
> there certainly arent any bytes left?

there are 2 bytes left because a 4 byte write failed to fit in 2 bytes

maybe bytestream2_get_bytes_left_p() should be made to return 0 once eof is
set even if space remains


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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