[FFmpeg-devel] [PATCH 5/6] avcodec/ffv1dec: consider run increase in minimal golomb frame size

[Michael Niedermayer]

On Thu, Jul 21, 2022 at 12:17:22AM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > On Tue, Jul 19, 2022 at 08:37:38AM -0300, James Almer wrote:
> >>
> >>
> >> On 7/19/2022 8:34 AM, Michael Niedermayer wrote:
> >>> Fixes: Timeout
> >>> Fixes: 49160/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFV1_fuzzer-5672826144686080
> >>>
> >>> 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/ffv1dec.c | 6 +++++-
> >>>   1 file changed, 5 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
> >>> index 01ddcaa512..9bdac0be4e 100644
> >>> --- a/libavcodec/ffv1dec.c
> >>> +++ b/libavcodec/ffv1dec.c
> >>> @@ -883,7 +883,11 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *rframe,
> >>>           if (buf_size < avctx->width * avctx->height / (128*8))
> >>>               return AVERROR_INVALIDDATA;
> >>>       } else {
> >>> -        if (buf_size < avctx->height / 8)
> >>> +        int i;
> >>
> >> for (int i...
> > 
> > will apply with that change
> > 
> > thx
> > 
> 
> James' suggestion made you use an uninitialized i in the actual check;

yes


> and even the original check is wrong, as one can overrun ff_log2_run
> (unless there is a check that I am not missing). 

Theres a check but its too late


> So it seems to me that
> reverting 15785e044ee1265464bb4f3ed727e2a8074f97b4 is appropriate.

not against that but heres a quick fix attempt


Author: Michael Niedermayer <michael at niedermayer.cc>
Date:   Thu Jul 21 00:20:41 2022 +0200

    avcodec/ffv1dec: Fix AC_GOLOMB_RICE min size check
    
    Found-by: mkver
    
    Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
index d71584505d..c6eca3227c 100644
--- a/libavcodec/ffv1dec.c
+++ b/libavcodec/ffv1dec.c
@@ -884,9 +884,14 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *rframe,
             return AVERROR_INVALIDDATA;
     } else {
         int w = avctx->width;
-        for (int i = 0; w > (1<<ff_log2_run[i]); i++)
+        int s = 1 + w / (1<<23);
+        int i;
+
+        w /= s;
+
+        for (i = 0; w > (1<<ff_log2_run[i]); i++)
             w -= ff_log2_run[i];
-        if (buf_size < (avctx->height + i + 6)/ 8)
+        if (buf_size < (avctx->height + s*i + 6)/ 8)
             return AVERROR_INVALIDDATA;
     }
 
 

[...]
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