[FFmpeg-devel] [PATCH 2/3] avcodec/pgxdec: Check depth more completely

[Andreas Rheinhardt]

Michael Niedermayer:
> On Fri, Oct 09, 2020 at 06:52:18PM +0200, Michael Niedermayer wrote:
>> On Thu, Oct 08, 2020 at 09:48:41PM +0200, Andreas Rheinhardt wrote:
>>> Michael Niedermayer:
>>>> Fixes: shift exponent -1 is negative
>>>> Fixes: 26107/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PGX_fuzzer-5378790047612928
>>>>
>>>> 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/pgxdec.c | 6 +++---
>>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/libavcodec/pgxdec.c b/libavcodec/pgxdec.c
>>>> index 150f8bbf66..5c735894ab 100644
>>>> --- a/libavcodec/pgxdec.c
>>>> +++ b/libavcodec/pgxdec.c
>>>> @@ -133,14 +133,14 @@ static int pgx_decode_frame(AVCodecContext *avctx, void *data,
>>>>      if ((ret = ff_set_dimensions(avctx, width, height)) < 0)
>>>>          return ret;
>>>>  
>>>> -    if (depth <= 8) {
>>>> +    if (depth > 0 && depth <= 8) {
>>>>          avctx->pix_fmt = AV_PIX_FMT_GRAY8;
>>>>          bpp = 8;
>>>> -    } else if (depth <= 16) {
>>>> +    } else if (depth > 0 && depth <= 16) {
>>>>          avctx->pix_fmt = AV_PIX_FMT_GRAY16;
>>>>          bpp = 16;
>>>>      } else {
>>>> -        av_log(avctx, AV_LOG_ERROR, "Maximum depth of 16 bits supported.\n");
>>>> +        av_log(avctx, AV_LOG_ERROR, "depth %d is invalid or unsupported.\n", depth);
>>>>          return AVERROR_PATCHWELCOME;
>>>>      }
>>>>      if (bytestream2_get_bytes_left(&g) < width * height * (bpp >> 3))
>>>>
>>> I presume the parsed depth to be zero in your testcase. Said number
>>> comes from pgx_get_number() which is only used to parse values for which
>>> a value of zero makes no sense. Wouldn't it make more sense to error out
>>> there if the number is zero?
>>
>> I was considering that too when i wrote the patch
>> the reason why i picked this is thats where depth is checked already.
>> Checking for depth == 0 in one function and depth > 16 in another feels
>> like its not the clearest way to implement that ...
> 
> ok if i apply this ? 
> or you still want it changed ?
> 
I don't care. Proceed as you want.

- Andreas