[FFmpeg-devel] [PATCH] Fix interlaced MPEG2 decoder crash (issue2367)

[Anatoly Nenashev]

Hi!
Full problem description available on https://roundup.ffmpeg.org/issue2367.
After some research I've found that sample file(exploit.bin) conflicts 
with specification in the following lines:

"In the case that a P field picture is used as the second field of a 
frame in which the first field is an I field
picture a series of semantic restrictions apply. These ensure that 
prediction is only made from the I field
picture. These restrictions are;
?        There shall be no macroblocks that are coded with 
macroblock_motion_forward zero and
          macroblock_intra zero.
?        Dual prime prediction shall not be used.
?        Field prediction in which motion_vertical_field_select 
indicates the same parity as the field
          being predicted shall not be used.
?        There shall be no skipped macroblocks."

So it looks like first and third restrictions are broken in sample file. 
Attached patch contains check for this situation.

Regards,
Anatoly.
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