avcodec/kmvc: Check side data size before use

Fixes out of array read
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/kmvc.c

@@ -268,7 +268,8 @@ static int decode_frame(AVCodecContext * avctx, void *data, int *got_frame,
     int i, ret;
     int header;
     int blocksize;
-    const uint8_t *pal = av_packet_get_side_data(avpkt, AV_PKT_DATA_PALETTE, NULL);
+    int pal_size;
+    const uint8_t *pal = av_packet_get_side_data(avpkt, AV_PKT_DATA_PALETTE, &pal_size);
 
     bytestream2_init(&ctx->g, avpkt->data, avpkt->size);
 
@@ -303,9 +304,11 @@ static int decode_frame(AVCodecContext * avctx, void *data, int *got_frame,
         }
     }
 
-    if (pal) {
+    if (pal && pal_size == AVPALETTE_SIZE) {
         frame->palette_has_changed = 1;
         memcpy(ctx->pal, pal, AVPALETTE_SIZE);
+    } else if (pal) {
+        av_log(avctx, AV_LOG_ERROR, "Palette size %d is wrong\n", pal_size);
     }
 
     if (ctx->setpal) {