diff --git a/include/net/route.h b/include/net/route.h
index dd4ae00..f68c167 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -313,12 +313,20 @@
 	return hoplimit;
 }
 
-static inline int ip_skb_dst_mtu(struct sk_buff *skb)
+static inline bool ip_sk_accept_pmtu(const struct sock *sk)
 {
-	struct inet_sock *inet = skb->sk ? inet_sk(skb->sk) : NULL;
+	return inet_sk(sk)->pmtudisc != IP_PMTUDISC_INTERFACE;
+}
 
-	return (inet && inet->pmtudisc == IP_PMTUDISC_PROBE) ?
-	       skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));
+static inline bool ip_sk_use_pmtu(const struct sock *sk)
+{
+	return inet_sk(sk)->pmtudisc < IP_PMTUDISC_PROBE;
+}
+
+static inline int ip_skb_dst_mtu(const struct sk_buff *skb)
+{
+	return (!skb->sk || ip_sk_use_pmtu(skb->sk)) ?
+	       dst_mtu(skb_dst(skb)) : skb_dst(skb)->dev->mtu;
 }
 
 #endif	/* _ROUTE_H */
diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index f9e8e49..393c5de 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -115,6 +115,11 @@
 #define IP_PMTUDISC_WANT		1	/* Use per route hints	*/
 #define IP_PMTUDISC_DO			2	/* Always DF		*/
 #define IP_PMTUDISC_PROBE		3       /* Ignore dst pmtu      */
+/* Always use interface mtu (ignores dst pmtu) but don't set DF flag.
+ * Also incoming ICMP frag_needed notifications will be ignored on
+ * this socket to prevent accepting spoofed ones.
+ */
+#define IP_PMTUDISC_INTERFACE		4
 
 #define IP_MULTICAST_IF			32
 #define IP_MULTICAST_TTL 		33
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 720c362..d9f65fc 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -174,6 +174,7 @@
 	mtu = dst_mtu(dst);
 
 	if (inet->pmtudisc != IP_PMTUDISC_DONT &&
+	    ip_sk_accept_pmtu(sk) &&
 	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {
 		dccp_sync_mss(sk, mtu);
 
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 51be64e..9124027 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1037,7 +1037,6 @@
 static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 			 struct ipcm_cookie *ipc, struct rtable **rtp)
 {
-	struct inet_sock *inet = inet_sk(sk);
 	struct ip_options_rcu *opt;
 	struct rtable *rt;
 
@@ -1063,8 +1062,8 @@
 	 * We steal reference to this route, caller should not release it
 	 */
 	*rtp = NULL;
-	cork->fragsize = inet->pmtudisc == IP_PMTUDISC_PROBE ?
-			 rt->dst.dev->mtu : dst_mtu(&rt->dst);
+	cork->fragsize = ip_sk_use_pmtu(sk) ?
+			 dst_mtu(&rt->dst) : rt->dst.dev->mtu;
 	cork->dst = &rt->dst;
 	cork->length = 0;
 	cork->ttl = ipc->ttl;
@@ -1315,7 +1314,8 @@
 	/* DF bit is set when we want to see DF on outgoing frames.
 	 * If local_df is set too, we still allow to fragment this frame
 	 * locally. */
-	if (inet->pmtudisc >= IP_PMTUDISC_DO ||
+	if (inet->pmtudisc == IP_PMTUDISC_DO ||
+	    inet->pmtudisc == IP_PMTUDISC_PROBE ||
 	    (skb->len <= dst_mtu(&rt->dst) &&
 	     ip_dont_fragment(sk, &rt->dst)))
 		df = htons(IP_DF);
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 0626f2c..3f85826 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -627,7 +627,7 @@
 		inet->nodefrag = val ? 1 : 0;
 		break;
 	case IP_MTU_DISCOVER:
-		if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_PROBE)
+		if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_INTERFACE)
 			goto e_inval;
 		inet->pmtudisc = val;
 		break;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d2d3253..f428935 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1036,6 +1036,10 @@
 	bool new = false;
 
 	bh_lock_sock(sk);
+
+	if (!ip_sk_accept_pmtu(sk))
+		goto out;
+
 	rt = (struct rtable *) __sk_dst_get(sk);
 
 	if (sock_owned_by_user(sk) || !rt) {
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 300ab2c..14bba8a 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -288,6 +288,7 @@
 	mtu = dst_mtu(dst);
 
 	if (inet->pmtudisc != IP_PMTUDISC_DONT &&
+	    ip_sk_accept_pmtu(sk) &&
 	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {
 		tcp_sync_mss(sk, mtu);