[FFmpeg-devel] [PATCH 6/9] avformat/vividas: Check for zero v_size

[Andreas Rheinhardt]

Michael Niedermayer:
> Fixes: SEGV on unknown address 0x000000000000
> Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavformat/vividas.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/vividas.c b/libavformat/vividas.c
> index 999c4a5d1c..6e93d96aef 100644
> --- a/libavformat/vividas.c
> +++ b/libavformat/vividas.c
> @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s,
>              return AVERROR_INVALIDDATA;
>  
>          ffio_read_varlen(pb);
> -        if (v_size > INT_MAX)
> +        if (v_size > INT_MAX || !v_size)
>              return AVERROR_INVALIDDATA;
>          ret = av_get_packet(pb, pkt, v_size);
>          if (ret < 0)
> @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s,
>      } else {
>          uint64_t v_size = ffio_read_varlen(pb);
>  
> -        if (v_size > INT_MAX)
> +        if (v_size > INT_MAX || !v_size)
>              return AVERROR_INVALIDDATA;
>          ret = av_get_packet(pb, pkt, v_size);
>          if (ret < 0)
> 
av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to
a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing
pkt->data[0] for the flags should not segfault (but it would set the
wrong result: that it is a keyframe). So where is the segfault?

- Andreas