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>

1 files changed, 24 insertions, 4 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8323136bdc5..a275c6e1e25 100644
--- 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
  */