indeo5: check tile size in decode_mb_info().

This prevents writing into a too small array if some parameters changed
without the tile being reallocated.

Fixes CVE-2012-2794

CC:libav-stable@libav.org

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/indeo5.c

@@ -430,6 +430,12 @@ static int decode_mb_info(IVI45DecContext *ctx, IVIBandDesc *band,
         ((band->qdelta_present && band->inherit_qdelta) || band->inherit_mv))
         return AVERROR_INVALIDDATA;
 
+    if (tile->num_MBs != IVI_MBs_PER_TILE(tile->width, tile->height, band->mb_size)) {
+        av_log(avctx, AV_LOG_ERROR, "Allocated tile size %d mismatches parameters %d\n",
+               tile->num_MBs, IVI_MBs_PER_TILE(tile->width, tile->height, band->mb_size));
+        return AVERROR_INVALIDDATA;
+    }
+
     /* scale factor for motion vectors */
     mv_scale = (ctx->planes[0].bands[0].mb_size >> 3) - (band->mb_size >> 3);
     mv_x = mv_y = 0;