Re: [FFmpeg-devel] [FFmpeg-cvslog] avformat/wtvdec: Initialize buf

From: Peter Ross <pross@xvid.org>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [FFmpeg-cvslog] avformat/wtvdec: Initialize buf
Date: Wed, 22 Jan 2025 19:02:07 +1100
Message-ID: <Z5Cl_6Qk14WjLOQj@db9113ea98d98dd28eac7beef2464e3c> (raw)
In-Reply-To: <20250121215744.2CBC24126D3@natalya.videolan.org>

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On Tue, Jan 21, 2025 at 09:57:43PM +0000, Michael Niedermayer wrote:
> ffmpeg | branch: master | Michael Niedermayer <michael@niedermayer.cc> | Thu Dec 26 02:53:45 2024 +0100| [17b019c517af26c6d2f0c6266938c60d36db1fa3] | committer: Michael Niedermayer
> 
> avformat/wtvdec: Initialize buf
> 
> ff_parse_mpeg2_descriptor() reads over what is initialized
> Fixes: use of uninitialized memory
> Fixes: 383825645/clusterfuzz-testcase-minimized-ffmpeg_dem_WTV_fuzzer-5144130618982400
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> 
> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=17b019c517af26c6d2f0c6266938c60d36db1fa3
> ---
> 
>  libavformat/wtvdec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
> index 730c7fca78..21c9649869 100644
> --- a/libavformat/wtvdec.c
> +++ b/libavformat/wtvdec.c
> @@ -833,7 +833,7 @@ static int parse_chunks(AVFormatContext *s, int mode, int64_t seekts, int *len_p
>              int stream_index = ff_find_stream_index(s, sid);
>              if (stream_index >= 0) {
>                  AVStream *st = s->streams[stream_index];
> -                uint8_t buf[258];
> +                uint8_t buf[258] = {0};
>                  const uint8_t *pbuf = buf;

hi michael,

can you help me understand why this is needed...
the avio_read() call fills buf, and the call to ff_parse_mpeg2_descriptor
specifies an "end" pointer (desc_list_end point) to prevent overreading.
where is the uninitialised memory coming from?

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)

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