diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
index d496c02e14bc44327fd3ab6c3faad0c1d7ac1e12..c15d8054905cc96ad4a4a9ca3d8bc4b5714ccca8 100644
--- a/include/uapi/linux/ipv6_route.h
+++ b/include/uapi/linux/ipv6_route.h
@@ -28,7 +28,7 @@
 
 #define RTF_ROUTEINFO	0x00800000	/* route information - RA	*/
 
-#define RTF_CACHE	0x01000000	/* cache entry			*/
+#define RTF_CACHE	0x01000000	/* read-only: can not be set by user */
 #define RTF_FLOW	0x02000000	/* flow significant route	*/
 #define RTF_POLICY	0x04000000	/* policy route			*/
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 605e5dc1c010e07530d85a369b6f8a041f9ee36d..70d9659fc1e9497e56e8955de338bd0b1d905fa4 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2478,6 +2478,12 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
 		goto out;
 	}
 
+	/* RTF_CACHE is an internal flag; can not be set by userspace */
+	if (cfg->fc_flags & RTF_CACHE) {
+		NL_SET_ERR_MSG(extack, "Userspace can not set RTF_CACHE");
+		goto out;
+	}
+
 	if (cfg->fc_dst_len > 128) {
 		NL_SET_ERR_MSG(extack, "Invalid prefix length");
 		goto out;