Clobbering these tables will temporarily clobber the template used
as a basis for other threads to start decoding from. If the other
decoding thread updates from the template right at that moment,
subsequent threads will get invalid (or, usually, none at all) mmco
tables. This leads to invalid reference lists and subsequent decode
failures.

Therefore, instead, decode the mmco tables only for the first slice in
a field or frame. For other slices, decode the bits and ensure they
are identical to the mmco tables in the first slice, but don't ever
clobber the context state. This prevents other threads from using a
clobbered/invalid template as starting point for decoding, and thus
fixes decoding in these cases.

This fixes occasional (~1%) failures of h264-conformance-mr1_bt_a with
frame-multithreading enabled.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Since resolution change support this also was exploitable, which is
how it was found.

Fixes read after free and out of array reads.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Reviewed-by: Derek Buitenhuis

Found-by: johnd and Paul B Mahol

Fix build failure without yasm
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

This could also be fixed by changing the argument type if
someone prefers that and wants to change it ...
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

There is only about 4 lines of common code, so it alot cleaner
when seperated.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

* qatar/master:
  rtmpproto: Fix assignments in if()
  lavf: Fix assignments in if()
  svq1enc: Fix assignments in if()
  lavc: Fix assignments in if() when calling ff_af_queue_add
  h264: Fix assignments in if()
  truemotion2: cosmetics, reformat

Conflicts:
	libavcodec/svq1enc.c
	libavcodec/truemotion2.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit 'df903683':
  truemotion2: return meaningful error codes.
  tscc: remove some pointless comments and empty lines.
  tscc: return meaningful error codes.
  loco: cosmetics, reformat

Conflicts:
	libavcodec/truemotion2.c
	libavcodec/tscc.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '1a31dff9':
  loco: return meaningful error codes.
  flicvideo: return meaningful error codes.
  vcr1: remove disabled encoder stub

Conflicts:
	libavcodec/flicvideo.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '74a9a624':
  vcr1: return a meaningful error code.
  rpza: return a meaningful error code.
  qdrw: cosmetics, reformat

Conflicts:
	libavcodec/qdrw.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '688b132b':
  qdrw: return meaningful error codes.
  qtrle: return a meaningful error code.
  gifdec: return meaningful error codes.
  interplayvideo: remove a static variable.
  interplayvideo: return meaningful error codes.
  lcldec: return meaningful error codes.
  targa: return meaningful error codes.
  qpeg: return a meaningful error code.
  nuv: return meaningful error codes.

Conflicts:
	libavcodec/gifdec.c
	libavcodec/interplayvideo.c
	libavcodec/nuv.c
	libavcodec/qpeg.c
	libavcodec/targa.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit 'a1c525f7':
  pcx: return meaningful error codes.
  tmv: return meaningful error codes.
  msrle: return meaningful error codes.
  cscd: return meaningful error codes.
  yadif: x86: fix build for compilers without aligned stack
  lavc: introduce the convenience function init_get_bits8
  lavc: check for overflow in init_get_bits

Conflicts:
	libavcodec/cscd.c
	libavcodec/pcx.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '90cfc084':
  avpacket: free side data in av_free_packet().
  v4l2: do not assert on a value received from outside of Libav
  v4l2: set the average framerate instead of codec timebase.

Conflicts:
	libavcodec/avpacket.c
	libavdevice/v4l2.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '246da0b1':
  v4l2: avoid pointless indirection.
  vdpau: Add VC-1 decoding via hwaccel infrastructure
  vdpau: Add H.264 decoding via hwaccel infrastructure

Conflicts:
	configure
	libavcodec/Makefile
	libavcodec/version.h
	libavdevice/v4l2.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '200e8ac9':
  vdpau: Add MPEG-4 decoding via hwaccel infrastructure
  vdpau: Add MPEG-1/2 decoding via hwaccel infrastructure

Conflicts:
	configure
	libavcodec/Makefile
	libavcodec/version.h
Merged-by: Michael Niedermayer <michaelni@gmx.at>

* commit '44e065d5':
  vdpau: Add context and common helpers for hwaccel support

Conflicts:
	Changelog
	doc/APIchanges
	libavcodec/vdpau.h
	libavcodec/version.h
Merged-by: Michael Niedermayer <michaelni@gmx.at>

Signed-off-by: Martin Storsjö <martin@martin.st>

Signed-off-by: Martin Storsjö <martin@martin.st>

Signed-off-by: Martin Storsjö <martin@martin.st>

Signed-off-by: Martin Storsjö <martin@martin.st>

Fixes null pointer dereference later, since if this function failed,
a positive return value was returned to the caller.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Martin Storsjö <martin@martin.st>