avcodec/8bps: Check side data size before use

Fixes out of array read
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 042faa84)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/8bps.c

@@ -119,12 +119,15 @@ static int decode_frame(AVCodecContext *avctx, void *data,
     }
 
     if (avctx->bits_per_coded_sample <= 8) {
+        int size;
         const uint8_t *pal = av_packet_get_side_data(avpkt,
                                                      AV_PKT_DATA_PALETTE,
-                                                     NULL);
-        if (pal) {
+                                                     &size);
+        if (pal && size == AVPALETTE_SIZE) {
             frame->palette_has_changed = 1;
             memcpy(c->pal, pal, AVPALETTE_SIZE);
+        } else if (pal) {
+            av_log(avctx, AV_LOG_ERROR, "Palette size %d is wrong\n", size);
         }
 
         memcpy (frame->data[1], c->pal, AVPALETTE_SIZE);