net/ipv6: Add helper to return path MTU based on fib result
Determine path MTU from a FIB lookup result. Logic is based on
ip6_dst_mtu_forward plus lookup of nexthop exception.
Add ip6_dst_mtu_forward to ipv6_stubs to handle access by core
bpf code.
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index cc24ed3b..dc5d5c8 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2603,6 +2603,54 @@ static unsigned int ip6_mtu(const struct dst_entry *dst)
return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
}
+/* MTU selection:
+ * 1. mtu on route is locked - use it
+ * 2. mtu from nexthop exception
+ * 3. mtu from egress device
+ *
+ * based on ip6_dst_mtu_forward and exception logic of
+ * rt6_find_cached_rt; called with rcu_read_lock
+ */
+u32 ip6_mtu_from_fib6(struct fib6_info *f6i, struct in6_addr *daddr,
+ struct in6_addr *saddr)
+{
+ struct rt6_exception_bucket *bucket;
+ struct rt6_exception *rt6_ex;
+ struct in6_addr *src_key;
+ struct inet6_dev *idev;
+ u32 mtu = 0;
+
+ if (unlikely(fib6_metric_locked(f6i, RTAX_MTU))) {
+ mtu = f6i->fib6_pmtu;
+ if (mtu)
+ goto out;
+ }
+
+ src_key = NULL;
+#ifdef CONFIG_IPV6_SUBTREES
+ if (f6i->fib6_src.plen)
+ src_key = saddr;
+#endif
+
+ bucket = rcu_dereference(f6i->rt6i_exception_bucket);
+ rt6_ex = __rt6_find_exception_rcu(&bucket, daddr, src_key);
+ if (rt6_ex && !rt6_check_expired(rt6_ex->rt6i))
+ mtu = dst_metric_raw(&rt6_ex->rt6i->dst, RTAX_MTU);
+
+ if (likely(!mtu)) {
+ struct net_device *dev = fib6_info_nh_dev(f6i);
+
+ mtu = IPV6_MIN_MTU;
+ idev = __in6_dev_get(dev);
+ if (idev && idev->cnf.mtu6 > mtu)
+ mtu = idev->cnf.mtu6;
+ }
+
+ mtu = min_t(unsigned int, mtu, IP6_MAX_MTU);
+out:
+ return mtu - lwtunnel_headroom(fib6_info_nh_lwt(f6i), mtu);
+}
+
struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
struct flowi6 *fl6)
{