[FFmpeg-devel] [PATCH 2/2] avcodec/rscc: Avoid returning frames that have nearly no undamaged pixels in them

[Matthew Fearnley]

> On 18 Jan 2019, at 23:00, Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
> Fixes: Timeout
> Fixes: 12192/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264
> 
> Before: clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264 in 15423 ms
> After:  clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264 in 190 ms
> 
> 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/rscc.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/rscc.c b/libavcodec/rscc.c
> index 7921f149ed..3868c1cb1b 100644
> --- a/libavcodec/rscc.c
> +++ b/libavcodec/rscc.c
> @@ -64,6 +64,7 @@ typedef struct RsccContext {
>     /* zlib interaction */
>     uint8_t *inflated_buf;
>     uLongf inflated_size;
> +    int valid_pixels
> } RsccContext;
> 
> static av_cold int rscc_init(AVCodecContext *avctx)
> @@ -348,7 +349,11 @@ static int rscc_decode_frame(AVCodecContext *avctx, void *data,
>         memcpy (frame->data[1], ctx->palette, AVPALETTE_SIZE);
>     }
> 
> -    *got_frame = 1;
> +    // We only return a picture when too little is undameged, this avoids copying nearly broken frames around
Hi,
FWIW, I think “too little is undameged” should say: “enough of it is undamaged”
(i.e. invert the logic, fix the typo).

> +    if (ctx->valid_pixels < ctx->inflated_size)
> +        ctx->valid_pixels += pixel_size;
> +    if (ctx->valid_pixels >= ctx->inflated_size * (100 - avctx->discard_damaged_percentage) / 100)
> +        *got_frame = 1;
> 
>     ret = avpkt->size;
> end:
> -- 
> 2.20.1
> 
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