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ipv6: Handle PMTU in ICMP error handlers.

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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>
This commit is contained in:
David S. Miller
2012-06-15 14:54:11 -07:00
parent 3639339553
commit 81aded2467
10 changed files with 54 additions and 122 deletions
Download Patch File Download Diff File Expand all files Collapse all files

143
net/ipv6/route.c
View File

@@ -1049,7 +1049,10 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
{
struct rt6_info *rt6 = (struct rt6_info*)dst;
dst_confirm(dst);
if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128) {
struct net *net = dev_net(dst->dev);
rt6->rt6i_flags |= RTF_MODIFIED;
if (mtu < IPV6_MIN_MTU) {
u32 features = dst_metric(dst, RTAX_FEATURES);
@@ -1058,9 +1061,39 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
dst_metric_set(dst, RTAX_FEATURES, features);
}
dst_metric_set(dst, RTAX_MTU, mtu);
rt6_update_expires(rt6, net->ipv6.sysctl.ip6_rt_mtu_expires);
}
}
void ip6_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
int oif, __be32 mark)
{
const struct ipv6hdr *iph = (struct ipv6hdr *) skb->data;
struct dst_entry *dst;
struct flowi6 fl6;
memset(&fl6, 0, sizeof(fl6));
fl6.flowi6_oif = oif;
fl6.flowi6_mark = mark;
fl6.flowi6_flags = FLOWI_FLAG_PRECOW_METRICS;
fl6.daddr = iph->daddr;
fl6.saddr = iph->saddr;
fl6.flowlabel = (*(__be32 *) iph) & IPV6_FLOWINFO_MASK;
dst = ip6_route_output(net, NULL, &fl6);
if (!dst->error)
ip6_rt_update_pmtu(dst, ntohl(mtu));
dst_release(dst);
}
EXPORT_SYMBOL_GPL(ip6_update_pmtu);
void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu)
{
ip6_update_pmtu(skb, sock_net(sk), mtu,
sk->sk_bound_dev_if, sk->sk_mark);
}
EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu);
static unsigned int ip6_default_advmss(const struct dst_entry *dst)
{
struct net_device *dev = dst->dev;
@@ -1703,116 +1736,6 @@ out:
dst_release(&rt->dst);
}
/*
* Handle ICMP "packet too big" messages
* i.e. Path MTU discovery
*/
static void rt6_do_pmtu_disc(const struct in6_addr *daddr, const struct in6_addr *saddr,
struct net *net, u32 pmtu, int ifindex)
{
struct rt6_info *rt, *nrt;
int allfrag = 0;
again:
rt = rt6_lookup(net, daddr, saddr, ifindex, 0);
if (!rt)
return;
if (rt6_check_expired(rt)) {
ip6_del_rt(rt);
goto again;
}
if (pmtu >= dst_mtu(&rt->dst))
goto out;
if (pmtu < IPV6_MIN_MTU) {
/*
* According to RFC2460, PMTU is set to the IPv6 Minimum Link
* MTU (1280) and a fragment header should always be included
* after a node receiving Too Big message reporting PMTU is
* less than the IPv6 Minimum Link MTU.
*/
pmtu = IPV6_MIN_MTU;
allfrag = 1;
}
/* New mtu received -> path was valid.
They are sent only in response to data packets,
so that this nexthop apparently is reachable. --ANK
*/
dst_confirm(&rt->dst);
/* Host route. If it is static, it would be better
not to override it, but add new one, so that
when cache entry will expire old pmtu
would return automatically.
*/
if (rt->rt6i_flags & RTF_CACHE) {
dst_metric_set(&rt->dst, RTAX_MTU, pmtu);
if (allfrag) {
u32 features = dst_metric(&rt->dst, RTAX_FEATURES);
features |= RTAX_FEATURE_ALLFRAG;
dst_metric_set(&rt->dst, RTAX_FEATURES, features);
}
rt6_update_expires(rt, net->ipv6.sysctl.ip6_rt_mtu_expires);
rt->rt6i_flags |= RTF_MODIFIED;
goto out;
}
/* Network route.
Two cases are possible:
1. It is connected route. Action: COW
2. It is gatewayed route or NONEXTHOP route. Action: clone it.
*/
if (!dst_get_neighbour_noref_raw(&rt->dst) && !(rt->rt6i_flags & RTF_NONEXTHOP))
nrt = rt6_alloc_cow(rt, daddr, saddr);
else
nrt = rt6_alloc_clone(rt, daddr);
if (nrt) {
dst_metric_set(&nrt->dst, RTAX_MTU, pmtu);
if (allfrag) {
u32 features = dst_metric(&nrt->dst, RTAX_FEATURES);
features |= RTAX_FEATURE_ALLFRAG;
dst_metric_set(&nrt->dst, RTAX_FEATURES, features);
}
/* According to RFC 1981, detecting PMTU increase shouldn't be
* happened within 5 mins, the recommended timer is 10 mins.
* Here this route expiration time is set to ip6_rt_mtu_expires
* which is 10 mins. After 10 mins the decreased pmtu is expired
* and detecting PMTU increase will be automatically happened.
*/
rt6_update_expires(nrt, net->ipv6.sysctl.ip6_rt_mtu_expires);
nrt->rt6i_flags |= RTF_DYNAMIC;
ip6_ins_rt(nrt);
}
out:
dst_release(&rt->dst);
}
void rt6_pmtu_discovery(const struct in6_addr *daddr, const 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
*/