vqavideo: return error if image size is not a multiple of block size

The decoder assumes in various places that the image size
is a multiple of the block size, and there is no obvious
way to support odd sizes.  Bailing out early if the header
specifies a bad size avoids various errors later on.

Fixes CVE-2012-0947.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/vqavideo.c

@@ -151,6 +151,12 @@ static av_cold int vqa_decode_init(AVCodecContext *avctx)
         return -1;
     }
 
+    if (s->width  & (s->vector_width  - 1) ||
+        s->height & (s->vector_height - 1)) {
+        av_log(avctx, AV_LOG_ERROR, "Image size not multiple of block size\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     /* allocate codebooks */
     s->codebook_size = MAX_CODEBOOK_SIZE;
     s->codebook = av_malloc(s->codebook_size);