net: Fix IPv6 PMTU disc. w/ asymmetric routes

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8323136..a275c6e 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1556,14 +1556,13 @@ out:
  *     i.e. Path MTU discovery
  */
 
-void rt6_pmtu_discovery(struct in6_addr *daddr, struct in6_addr *saddr,
-                       struct net_device *dev, u32 pmtu)
+static void rt6_do_pmtu_disc(struct in6_addr *daddr, struct in6_addr *saddr,
+                            struct net *net, u32 pmtu, int ifindex)
 {
        struct rt6_info *rt, *nrt;
-       struct net *net = dev_net(dev);
        int allfrag = 0;
 
-       rt = rt6_lookup(net, daddr, saddr, dev->ifindex, 0);
+       rt = rt6_lookup(net, daddr, saddr, ifindex, 0);
        if (rt == NULL)
                return;
 
@@ -1631,6 +1630,27 @@ out:
        dst_release(&rt->dst);
 }
 
+void rt6_pmtu_discovery(struct in6_addr *daddr, struct in6_addr *saddr,
+                       struct net_device *dev, u32 pmtu)
+{
+       struct net *net = dev_net(dev);
+
+       /*
+        * RFC 1981 states that a node "MUST reduce the size of the packets it
+        * is sending along the path" that caused the Packet Too Big message.
+        * Since it's not possible in the general case to determine which
+        * interface was used to send the original packet, we update the MTU
+        * on the interface that will be used to send future packets. We also
+        * update the MTU on the interface that received the Packet Too Big in
+        * case the original packet was forced out that interface with
+        * SO_BINDTODEVICE or similar. This is the next best thing to the
+        * correct behaviour, which would be to update the MTU on all
+        * interfaces.
+        */
+       rt6_do_pmtu_disc(daddr, saddr, net, pmtu, 0);
+       rt6_do_pmtu_disc(daddr, saddr, net, pmtu, dev->ifindex);
+}
+
 /*
  *     Misc support functions
  */