Re: [FFmpeg-devel] [PATCH 4/4] avcodec/evc_parse: Check tid

["Dawid Kozinski/Multimedia \(PLT\) /SRPOL/Staff Engineer/Samsung Electronics" <d.kozinski@samsung.com>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> Michael Niedermayer
> Sent: czwartek, 5 października 2023 00:59
> To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> Subject: [FFmpeg-devel] [PATCH 4/4] avcodec/evc_parse: Check tid
> 
> The check is based on not infinite looping. It is likely a more strict
check can be
> done
> 
> Fixes: Infinite loop
> Fixes: 62473/clusterfuzz-testcase-minimized-
> ffmpeg_BSF_EVC_FRAME_MERGE_fuzzer-5719883750703104
> 
> Found-by: continuous fuzzing process
> https://protect2.fireeye.com/v1/url?k=a44f565e-c532bcdd-a44edd11-
> 74fe48600158-625c91e4183f7607&q=1&e=5e707773-ad1c-4987-a095-
> 2350d52c5cd3&u=https%3A%2F%2Fgithub.com%2Fgoogle%2Foss-
> fuzz%2Ftree%2Fmaster%2Fprojects%2Fffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/evc_parse.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libavcodec/evc_parse.c b/libavcodec/evc_parse.c index
> 20b6849041a..8c0ef16f3ad 100644
> --- a/libavcodec/evc_parse.c
> +++ b/libavcodec/evc_parse.c
> @@ -178,6 +178,9 @@ int ff_evc_derive_poc(const EVCParamSets *ps, const
> EVCParserSliceHeader *sh,
>          } else {
>              int SubGopLength = 1 << sps->log2_sub_gop_length;
> 
> +            if (tid > 1 + av_log2(SubGopLength - 1))
> +                return AVERROR_INVALIDDATA;
> +
>              if (tid == 0) {
>                  poc->PicOrderCntVal = poc->prevPicOrderCntVal +
SubGopLength;
>                  poc->DocOffset = 0;

int SubGopLength = 1 << sps->log2_sub_gop_length; if (tid > 1 +
av_log2(SubGopLength - 1))
	return AVERROR_INVALIDDATA;

For the value of SubGopLength = 1 ( if sps->log2_sub_gop_length  = 0; "The
value of log2_sub_gop_length shall be in the range of 0 to 5, inclusive" -
ISO_IEC_23094-1-2020 7.4.3.1), we have av_log2(0). The value of the
logarithm of 0 with any base (in this case, log2) is minus infinity (-inf)

Perhaps we should consider changing the condition to:
if (tid < 0 || tid > av_log2(SubGopLength))
                return AVERROR_INVALIDDATA;

> --
> 2.17.1
> 
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