[FFmpeg-trac] #764(avcodec:new): Increasing robustness of runlength decoding for scantable access in mpeg12.c

FFmpeg trac at avcodec.org
Fri Dec 16 23:13:39 CET 2011


#764: Increasing robustness of runlength decoding for scantable access in
mpeg12.c
-------------------------------------+-------------------------------------
             Reporter:  erik         |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:  avcodec
              Version:  unspecified  |               Resolution:
             Keywords:  mpeg         |               Blocked By:
  robustness                         |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by reimar):

 > Part of the scantable access is done by type array indexing but the last
 use case is done by pointer arithmic

 Valgrind runs the executable on an emulated CPU. What the source code
 looks like has no relevance. However valgind can sometimes miss a bad
 access if there is valid memory, but it is rather unlikely.

 > The wrong index was -31023 or something in that range so adding a bit to
 the table won't help.

 The run comes out of a VLC table. The VLC table should never contain an
 entry for a run length outside the 0 - 63 range or something like that.
 Thus I can't see how you should be able to get that value except by
 corrupt VLC tables.
 Haven't yet tested the sample.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/764#comment:10>
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