2 files changed, 17 insertions, 4 deletions

diff --git a/include/net/route.h b/include/net/route.h
index dd4ae0029fd8..f68c167280a7 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -313,12 +313,20 @@ static inline int ip4_dst_hoplimit(const struct dst_entry *dst)
         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 f9e8e496ae5d..393c5de09d42 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -115,6 +115,11 @@ struct in_addr {
 #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