[FFmpeg-devel] [PATCH 3/4] avcodec/h264_parser: Fix nalsize check

Andreas Rheinhardt andreas.rheinhardt at outlook.com
Sun Sep 5 22:51:32 EEST 2021


Michael Niedermayer:
> Fixes: Assertion failure
> Fixes: 37463/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-4914693494931456
> 
> 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/h264_parser.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/h264_parser.c b/libavcodec/h264_parser.c
> index 01ea016409..47cc1d5c78 100644
> --- a/libavcodec/h264_parser.c
> +++ b/libavcodec/h264_parser.c
> @@ -87,7 +87,7 @@ static int h264_find_frame_end(H264ParseContext *p, const uint8_t *buf,
>              i = next_avc;
>              for (j = 0; j < p->nal_length_size; j++)
>                  nalsize = (nalsize << 8) | buf[i++];
> -            if (!nalsize || nalsize > buf_size - i) {
> +            if (!nalsize || i > buf_size || nalsize > buf_size - i) {
>                  av_log(logctx, AV_LOG_ERROR, "AVC-parser: nal size %"PRIu32" "
>                         "remaining %d\n", nalsize, buf_size - i);
>                  return buf_size;
> 
The cheapest fix for this is to make nalsize int64_t. But actually this
whole code looks highly weird: In contrast to how the parsing API is
supposed to be, it requires the whole buffer being available, despite
the PARSER_FLAG_COMPLETE_FRAMES being unset.

- Andreas


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