commit 99230aeb0526e13056d8392ba91b1a73c3caabe6
author Yaowu Xu <yaowu@google.com> Wed Apr 16 12:22:49 2014 -0700
committer Yaowu Xu <yaowu@google.com> Wed Apr 16 13:00:13 2014 -0700
tree 48e808e6ba2877f13fbd98b600d4fef8801f7b56
parent 14331a84bd1fdadeb5bd1f3d0182d8aee6e0205a

Prevent reading of uninitialized value

This commit added a check of reference frame to make sure that pre
buffer pointers are initialized only when necessary and make them
to 0 if ref frame is intra, hence those buffer should never be used.

Change-Id: Ieb474fcd9feb759f02e2f9c282b7348a8fa31117

vp8/decoder/decodeframe.c

diff --git a/vp8/decoder/decodeframe.c b/vp8/decoder/decodeframe.c
index bfde599..14f611a 100644
--- a/vp8/decoder/decodeframe.c
+++ b/vp8/decoder/decodeframe.c
@@ -631,9 +631,17 @@
             xd->dst.u_buffer = dst_buffer[1] + recon_uvoffset;
             xd->dst.v_buffer = dst_buffer[2] + recon_uvoffset;
 
-            xd->pre.y_buffer = ref_buffer[xd->mode_info_context->mbmi.ref_frame][0] + recon_yoffset;
-            xd->pre.u_buffer = ref_buffer[xd->mode_info_context->mbmi.ref_frame][1] + recon_uvoffset;
-            xd->pre.v_buffer = ref_buffer[xd->mode_info_context->mbmi.ref_frame][2] + recon_uvoffset;
+            if (xd->mode_info_context->mbmi.ref_frame >= LAST_FRAME) {
+              MV_REFERENCE_FRAME ref = xd->mode_info_context->mbmi.ref_frame;
+              xd->pre.y_buffer = ref_buffer[ref][0] + recon_yoffset;
+              xd->pre.u_buffer = ref_buffer[ref][1] + recon_uvoffset;
+              xd->pre.v_buffer = ref_buffer[ref][2] + recon_uvoffset;
+            } else {
+              // ref_frame is INTRA_FRAME, pre buffer should not be used.
+              xd->pre.y_buffer = 0;
+              xd->pre.u_buffer = 0;
+              xd->pre.v_buffer = 0;
+            }
 
             /* propagate errors from reference frames */
             xd->corrupted |= ref_fb_corrupted[xd->mode_info_context->mbmi.ref_frame];