[FFmpeg-devel] [PATCH 1/5] avcodec/mpeg4videodec: Move decode_studiovisualobject() parsing in the branch for visual object parsing

[Michael Niedermayer]

On Sun, Apr 29, 2018 at 08:23:39PM +0000, Kieran Kunhya wrote:
> On Sun, 29 Apr 2018 at 20:20 Michael Niedermayer <michael at niedermayer.cc>
> wrote:
> 
> > Fixes: runtime error: shift exponent -1 is negative
> > Fixes:
> > 7510/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5024523356209152
> >
> > Found-by: continuous fuzzing process
> > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by
> > <https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by>:
> > Michael Niedermayer <michael at niedermayer.cc>
> >
> 
> No, this is wrong, extension_and_user_data( 0 ) may precede
> StudioVisualObject.

The code before this patch calls a single extension_and_user_data(0)
between VOS_STARTCODE and VISUAL_OBJ_STARTCODE

the code after this patch still does this.

The implementation for extension_and_user_data(0) does nothing though
everything the code does is behind a
if ((id == 2 || id == 4) && ...
so id == 0 does nothing

extension_and_user_data(0) should parse user data.
This was not done before this patch, but should work after the patch
as there is a entry in the main loop to parse user data.
The code before bypassed the main loop.

If there are no further objections i intend to apply this in a day or 2

Thanks

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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