ipv6: Handle PMTU in ICMP error handlers.

One tricky issue on the ipv6 side vs. ipv4 is that the ICMP callouts
to handle the error pass the 32-bit info cookie in network byte order
whereas ipv4 passes it around in host byte order.

Like the ipv4 side, we have two helper functions.  One for when we
have a socket context and one for when we do not.

ip6ip6 tunnels are not handled here, because they handle PMTU events
by essentially relaying another ICMP packet-too-big message back to
the original sender.

This patch allows us to get rid of rt6_do_pmtu_disc().  It handles all
kinds of situations that simply cannot happen when we do the PMTU
update directly using a fully resolved route.

In fact, the "plen == 128" check in ip6_rt_update_pmtu() can very
likely be removed or changed into a BUG_ON() check.  We should never
have a prefixed ipv6 route when we get there.

Another piece of strange history here is that TCP and DCCP, unlike in
ipv4, never invoke the update_pmtu() method from their ICMP error
handlers.  This is incredibly astonishing since this is the context
where we have the most accurate context in which to make a PMTU
update, namely we have a fully connected socket and associated cached
socket route.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index f05099fc5901..051ad481973f 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -479,6 +479,9 @@ void __udp6_lib_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
         if (sk == NULL)
                 return;
 
+        if (type == ICMPV6_PKT_TOOBIG)
+                ip6_sk_update_pmtu(skb, sk, info);
+
         np = inet6_sk(sk);
 
         if (!icmpv6_err_convert(type, code, &err) && !np->recverr)