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[FFmpeg-devel] avcodec/cbs_h264_syntax_template: fix off by 1 error with slice_group_change_cycle

Message ID 20200322230043.11552-1-michael@niedermayer.cc
State New
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Series [FFmpeg-devel] avcodec/cbs_h264_syntax_template: fix off by 1 error with slice_group_change_cycle
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Commit Message

Michael Niedermayer March 22, 2020, 11 p.m. UTC
Fixes: assertion failure
Fixes: 20390/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_REDUNDANT_PPS_fuzzer-5683400772157440

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/cbs_h264_syntax_template.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

James Almer March 23, 2020, 3:30 a.m. UTC | #1
On 3/22/2020 8:00 PM, Michael Niedermayer wrote:
> Fixes: assertion failure
> Fixes: 20390/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_REDUNDANT_PPS_fuzzer-5683400772157440
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/cbs_h264_syntax_template.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/cbs_h264_syntax_template.c b/libavcodec/cbs_h264_syntax_template.c
> index 878d348b94..b7e796e9a8 100644
> --- a/libavcodec/cbs_h264_syntax_template.c
> +++ b/libavcodec/cbs_h264_syntax_template.c
> @@ -1365,7 +1365,7 @@ static int FUNC(slice_header)(CodedBitstreamContext *ctx, RWContext *rw,
>          pic_size = (sps->pic_width_in_mbs_minus1 + 1) *
>                     (sps->pic_height_in_map_units_minus1 + 1);
>          max = (pic_size + pps->slice_group_change_rate_minus1) /
> -              (pps->slice_group_change_rate_minus1 + 1);
> +              (pps->slice_group_change_rate_minus1 + 1) + 1;

The spec says

"The value of slice_group_change_cycle is represented in the bitstream
by the following number of bits Ceil( Log2( PicSizeInMapUnits ÷
SliceGroupChangeRate + 1 ) )

The value of slice_group_change_cycle shall be in the range of 0 to
Ceil( PicSizeInMapUnits ÷ SliceGroupChangeRate ), inclusive."

Are you trying to change the amount of bits read, the max allowed value,
or both?

>          bits = av_log2(2 * max - 1);

This should use av_ceil_log2() IMO, so it's clear what it's trying to do.

>  
>          u(bits, slice_group_change_cycle, 0, max);
>
Michael Niedermayer March 23, 2020, 10:01 a.m. UTC | #2
On Mon, Mar 23, 2020 at 12:30:31AM -0300, James Almer wrote:
> On 3/22/2020 8:00 PM, Michael Niedermayer wrote:
> > Fixes: assertion failure
> > Fixes: 20390/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_REDUNDANT_PPS_fuzzer-5683400772157440
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/cbs_h264_syntax_template.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavcodec/cbs_h264_syntax_template.c b/libavcodec/cbs_h264_syntax_template.c
> > index 878d348b94..b7e796e9a8 100644
> > --- a/libavcodec/cbs_h264_syntax_template.c
> > +++ b/libavcodec/cbs_h264_syntax_template.c
> > @@ -1365,7 +1365,7 @@ static int FUNC(slice_header)(CodedBitstreamContext *ctx, RWContext *rw,
> >          pic_size = (sps->pic_width_in_mbs_minus1 + 1) *
> >                     (sps->pic_height_in_map_units_minus1 + 1);
> >          max = (pic_size + pps->slice_group_change_rate_minus1) /
> > -              (pps->slice_group_change_rate_minus1 + 1);
> > +              (pps->slice_group_change_rate_minus1 + 1) + 1;
> 
> The spec says
> 
> "The value of slice_group_change_cycle is represented in the bitstream
> by the following number of bits Ceil( Log2( PicSizeInMapUnits ÷
> SliceGroupChangeRate + 1 ) )
> 
> The value of slice_group_change_cycle shall be in the range of 0 to
> Ceil( PicSizeInMapUnits ÷ SliceGroupChangeRate ), inclusive."
> 
> Are you trying to change the amount of bits read, the max allowed value,
> or both?

the bits, ill send a better patch

thanks
diff mbox series

Patch

diff --git a/libavcodec/cbs_h264_syntax_template.c b/libavcodec/cbs_h264_syntax_template.c
index 878d348b94..b7e796e9a8 100644
--- a/libavcodec/cbs_h264_syntax_template.c
+++ b/libavcodec/cbs_h264_syntax_template.c
@@ -1365,7 +1365,7 @@  static int FUNC(slice_header)(CodedBitstreamContext *ctx, RWContext *rw,
         pic_size = (sps->pic_width_in_mbs_minus1 + 1) *
                    (sps->pic_height_in_map_units_minus1 + 1);
         max = (pic_size + pps->slice_group_change_rate_minus1) /
-              (pps->slice_group_change_rate_minus1 + 1);
+              (pps->slice_group_change_rate_minus1 + 1) + 1;
         bits = av_log2(2 * max - 1);
 
         u(bits, slice_group_change_cycle, 0, max);