From 0be513e8e881d263a9eec27c6cf3add3bc2d2316 Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Sat, 22 Apr 2017 13:11:16 -0700
Subject: [PATCH] webm_read_frame: avoid NULL dereference

block may be NULL with block_entry_eos or from return of GetBlock()

Change-Id: Ia0dd3ffa46305ee70efcdc55c05c2ad24efc993b
---
 webmdec.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/webmdec.cc b/webmdec.cc
index ed4bd700d..d609075a9 100644
--- a/webmdec.cc
+++ b/webmdec.cc
@@ -165,10 +165,11 @@ int webm_read_frame(struct WebmInputContext *webm_ctx, uint8_t **buffer,
     }
     if (get_new_block) {
       block = block_entry->GetBlock();
+      if (block == NULL) return -1;
       webm_ctx->block_frame_index = 0;
     }
-  } while (block->GetTrackNumber() != webm_ctx->video_track_index ||
-           block_entry_eos);
+  } while (block_entry_eos ||
+           block->GetTrackNumber() != webm_ctx->video_track_index);
 
   webm_ctx->cluster = cluster;
   webm_ctx->block_entry = block_entry;