iff: validate CMAP palette size

Fixes CVE-2013-2495

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

CC: libav-stable@libav.org

libavformat/iff.c

@@ -166,6 +166,11 @@ static int iff_read_header(AVFormatContext *s)
             break;
 
         case ID_CMAP:
+            if (data_size < 3 || data_size > 768 || data_size % 3) {
+                 av_log(s, AV_LOG_ERROR, "Invalid CMAP chunk size %d\n",
+                        data_size);
+                 return AVERROR_INVALIDDATA;
+            }
             st->codec->extradata_size = data_size;
             st->codec->extradata      = av_malloc(data_size);
             if (!st->codec->extradata)