palemoon-dev/platform/media/libvpx/clamp_abs_lvl_seg.patch

# HG changeset patch
# User Gerald Squelart <gsquelart@mozilla.com>
# Parent  b9e641a34c2fb9e6f3d3a02200bc2d800b6ca168
Bug 1224363 - Clamp seg_lvl also in abs-value mode - r=rillian

Even when the segment feature data is in absolute mode, it is still read as a
6-bit value with an added sign, so it could have values between -63 and +63.
Later, this signed value is used without checks as a filter level, which is
used to access an entry in an array of size MAX_LOOP_FILTER+1=64.

This patch just extends the existing clamping (that was done only to relative-
mode data) to absolute mode data, before it is blindly 'memset' in
lfi->lvl[seg][0], which was where the out-of-bound filter_value was read in
subsequent vp8_loop_filter_row_simple.

diff --git a/media/libvpx/vp8/common/loopfilter.c b/media/libvpx/vp8/common/loopfilter.c
--- a/media/libvpx/vp8/common/loopfilter.c
+++ b/media/libvpx/vp8/common/loopfilter.c
@@ -136,18 +136,18 @@ void vp8_loop_filter_frame_init(VP8_COMM
             /* Abs value */
             if (mbd->mb_segement_abs_delta == SEGMENT_ABSDATA)
             {
                 lvl_seg = mbd->segment_feature_data[MB_LVL_ALT_LF][seg];
             }
             else  /* Delta Value */
             {
                 lvl_seg += mbd->segment_feature_data[MB_LVL_ALT_LF][seg];
-                lvl_seg = (lvl_seg > 0) ? ((lvl_seg > 63) ? 63: lvl_seg) : 0;
             }
+            lvl_seg = (lvl_seg > 0) ? ((lvl_seg > 63) ? 63: lvl_seg) : 0;
         }
 
         if (!mbd->mode_ref_lf_delta_enabled)
         {
             /* we could get rid of this if we assume that deltas are set to
              * zero when not in use; encoder always uses deltas
              */
             memset(lfi->lvl[seg][0], lvl_seg, 4 * 4 );