--- linux-4.9.37/net/netlabel/netlabel_kapi.c	2017-07-12 16:42:41.000000000 +0300
+++ linux-4.9.y/net/netlabel/netlabel_kapi.c	2021-06-07 13:01:34.000000000 +0300
@@ -748,6 +748,12 @@
 	if ((off & (BITS_PER_LONG - 1)) != 0)
 		return -EINVAL;
 
+	/* a null catmap is equivalent to an empty one */
+	if (!catmap) {
+		*offset = (u32)-1;
+		return 0;
+	}
+
 	if (off < catmap->startbit) {
 		off = catmap->startbit;
 		*offset = off;