Merge "Prevent decoder from using uninitialized entropy context."

vp9/common/vp9_entropymode.c

diff --git a/vp9/common/vp9_entropymode.c b/vp9/common/vp9_entropymode.c
index d7610ed..0edc4f9 100644
--- a/vp9/common/vp9_entropymode.c
+++ b/vp9/common/vp9_entropymode.c
@@ -453,6 +453,7 @@
   vp9_default_coef_probs(cm);
   vp9_init_mode_probs(cm->fc);
   vp9_init_mv_probs(cm);
+  cm->fc->initialized = 1;
 
   if (cm->frame_type == KEY_FRAME ||
       cm->error_resilient_mode || cm->reset_frame_context == 3) {

vp9/common/vp9_entropymode.h

diff --git a/vp9/common/vp9_entropymode.h b/vp9/common/vp9_entropymode.h
index 6831d3f..6db1080 100644
--- a/vp9/common/vp9_entropymode.h
+++ b/vp9/common/vp9_entropymode.h
@@ -50,6 +50,7 @@
   struct tx_probs tx_probs;
   vp9_prob skip_probs[SKIP_CONTEXTS];
   nmv_context nmvc;
+  int initialized;
 } FRAME_CONTEXT;
 
 typedef struct {

vp9/decoder/vp9_decodeframe.c

diff --git a/vp9/decoder/vp9_decodeframe.c b/vp9/decoder/vp9_decodeframe.c
index 58df87d..5bf44d7 100644
--- a/vp9/decoder/vp9_decodeframe.c
+++ b/vp9/decoder/vp9_decodeframe.c
@@ -1556,6 +1556,10 @@
   vp9_setup_block_planes(xd, cm->subsampling_x, cm->subsampling_y);
 
   *cm->fc = cm->frame_contexts[cm->frame_context_idx];
+  if (!cm->fc->initialized)
+    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
+                       "Uninitialized entropy context.");
+
   vp9_zero(cm->counts);
 
   xd->corrupted = 0;