7 files changed, 28 insertions, 9 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
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 720c36225ed9..d9f65fc66db5 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -174,6 +174,7 @@ static inline void dccp_do_pmtu_discovery(struct sock *sk,
         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 51be64e18e32..912402752f2f 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1037,7 +1037,6 @@ error:
 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 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
          * 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 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
         /* 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 0626f2cb192e..3f858266fa7e 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -627,7 +627,7 @@ static int do_ip_setsockopt(struct sock *sk, int level,
                 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 d2d325382b13..f428935c50db 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1036,6 +1036,10 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
         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 300ab2c93f29..14bba8a1c5a7 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -288,6 +288,7 @@ static void tcp_v4_mtu_reduced(struct sock *sk)
         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);