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, 1 insertions, 5 deletions

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index ed89bba..5247d5c 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -649,7 +649,6 @@ static int icmpv6_rcv(struct sk_buff *skb)
 	struct net_device *dev = skb->dev;
 	struct inet6_dev *idev = __in6_dev_get(dev);
 	const struct in6_addr *saddr, *daddr;
-	const struct ipv6hdr *orig_hdr;
 	struct icmp6hdr *hdr;
 	u8 type;
 
@@ -661,7 +660,7 @@ static int icmpv6_rcv(struct sk_buff *skb)
 				 XFRM_STATE_ICMP))
 			goto drop_no_count;
 
-		if (!pskb_may_pull(skb, sizeof(*hdr) + sizeof(*orig_hdr)))
+		if (!pskb_may_pull(skb, sizeof(*hdr) + sizeof(struct ipv6hdr)))
 			goto drop_no_count;
 
 		nh = skb_network_offset(skb);
@@ -722,9 +721,6 @@ static int icmpv6_rcv(struct sk_buff *skb)
 		if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 			goto discard_it;
 		hdr = icmp6_hdr(skb);
-		orig_hdr = (struct ipv6hdr *) (hdr + 1);
-		rt6_pmtu_discovery(&orig_hdr->daddr, &orig_hdr->saddr, dev,
-				   ntohl(hdr->icmp6_mtu));
 
 		/*
 		 *	Drop through to notify