diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 688ba5f7516b37..8fe58a2d305c1e 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1206,14 +1206,16 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
 	v6_cork->tclass = ipc6->tclass;
 	if (rt->dst.flags & DST_XFRM_TUNNEL)
 		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
-		      rt->dst.dev->mtu : dst_mtu(&rt->dst);
+		      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(&rt->dst);
 	else
 		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
-		      rt->dst.dev->mtu : dst_mtu(rt->dst.path);
+		      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(rt->dst.path);
 	if (np->frag_size < mtu) {
 		if (np->frag_size)
 			mtu = np->frag_size;
 	}
+	if (mtu < IPV6_MIN_MTU)
+		return -EINVAL;
 	cork->base.fragsize = mtu;
 	if (dst_allfrag(rt->dst.path))
 		cork->base.flags |= IPCORK_ALLFRAG;