check block length

patch from ffmpeg to fix CVE-2013-0845

Change-Id: I5d228ff84c1ff9fd2c34b731eb71b76c5560c89c

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index f356a70..2746725 100644 (file)
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -551,12 +551,15 @@ static void get_block_sizes(ALSDecContext *ctx, unsigned int *div_blocks,
 
 /** Read the block data for a constant block
  */
-static void read_const_block_data(ALSDecContext *ctx, ALSBlockData *bd)
+static int read_const_block_data(ALSDecContext *ctx, ALSBlockData *bd)
 {
     ALSSpecificConfig *sconf = &ctx->sconf;
     AVCodecContext *avctx    = ctx->avctx;
     GetBitContext *gb        = &ctx->gb;
 
+    if (bd->block_length <= 0)
+        return AVERROR_INVALIDDATA;
+
     *bd->raw_samples = 0;
     *bd->const_block = get_bits1(gb);    // 1 = constant value, 0 = zero block (silence)
     bd->js_blocks    = get_bits1(gb);
@@ -571,6 +574,8 @@ static void read_const_block_data(ALSDecContext *ctx, ALSBlockData *bd)
 
     // ensure constant block decoding by reusing this field
     *bd->const_block = 1;
+
+    return 0;
 }
 
 
@@ -972,7 +977,7 @@ static int read_block(ALSDecContext *ctx, ALSBlockData *bd)
     if (get_bits1(gb)) {
         ret = read_var_block_data(ctx, bd);
     } else {
-        read_const_block_data(ctx, bd);
+        ret = read_const_block_data(ctx, bd);
     }
 
     return ret;