avcodec/cinepak: Check side data size before use

Fixes out of array read

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 121be31060)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cinepak.c

@@ -443,10 +443,13 @@ static int cinepak_decode_frame(AVCodecContext *avctx,
         return ret;
 
     if (s->palette_video) {
-        const uint8_t *pal = av_packet_get_side_data(avpkt, AV_PKT_DATA_PALETTE, NULL);
-        if (pal) {
+        int size;
+        const uint8_t *pal = av_packet_get_side_data(avpkt, AV_PKT_DATA_PALETTE, &size);
+        if (pal && size == AVPALETTE_SIZE) {
             s->frame->palette_has_changed = 1;
             memcpy(s->pal, pal, AVPALETTE_SIZE);
+        } else if (pal) {
+            av_log(avctx, AV_LOG_ERROR, "Palette size %d is wrong\n", size);
         }
     }