net: flow: Add l3mdev flow update

Add l3mdev hook to set FLOWI_FLAG_SKIP_NH_OIF flag and update oif/iif
in flow struct if its oif or iif points to a device enslaved to an L3
Master device. Only 1 needs to be converted to match the l3mdev FIB
rule. This moves the flow adjustment for l3mdev to a single point
catching all lookups. It is redundant for existing hooks (those are
removed in later patches) but is needed for missed lookups such as
PMTU updates.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/l3mdev.h

@@ -49,6 +49,8 @@ struct l3mdev_ops {
 int l3mdev_fib_rule_match(struct net *net, struct flowi *fl,
 			  struct fib_lookup_arg *arg);
 
+void l3mdev_update_flow(struct net *net, struct flowi *fl);
+
 int l3mdev_master_ifindex_rcu(const struct net_device *dev);
 static inline int l3mdev_master_ifindex(struct net_device *dev)
 {
@@ -290,6 +292,10 @@ int l3mdev_fib_rule_match(struct net *net, struct flowi *fl,
 {
 	return 1;
 }
+static inline
+void l3mdev_update_flow(struct net *net, struct flowi *fl)
+{
+}
 #endif
 
 #endif /* _NET_L3MDEV_H_ */

net/ipv4/fib_rules.c

@@ -56,6 +56,9 @@ int __fib_lookup(struct net *net, struct flowi4 *flp,
 	};
 	int err;
 
+	/* update flow if oif or iif point to device enslaved to l3mdev */
+	l3mdev_update_flow(net, flowi4_to_flowi(flp));
+
 	err = fib_rules_lookup(net->ipv4.rules_ops, flowi4_to_flowi(flp), 0, &arg);
 #ifdef CONFIG_IP_ROUTE_CLASSID
 	if (arg.rule)

net/ipv6/fib6_rules.c

@@ -38,6 +38,9 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 		.flags = FIB_LOOKUP_NOREF,
 	};
 
+	/* update flow if oif or iif point to device enslaved to l3mdev */
+	l3mdev_update_flow(net, flowi6_to_flowi(fl6));
+
 	fib_rules_lookup(net->ipv6.fib6_rules_ops,
 			 flowi6_to_flowi(fl6), flags, &arg);
 

net/l3mdev/l3mdev.c

@@ -222,3 +222,38 @@ out:
 
 	return rc;
 }
+
+void l3mdev_update_flow(struct net *net, struct flowi *fl)
+{
+	struct net_device *dev;
+	int ifindex;
+
+	rcu_read_lock();
+
+	if (fl->flowi_oif) {
+		dev = dev_get_by_index_rcu(net, fl->flowi_oif);
+		if (dev) {
+			ifindex = l3mdev_master_ifindex_rcu(dev);
+			if (ifindex) {
+				fl->flowi_oif = ifindex;
+				fl->flowi_flags |= FLOWI_FLAG_SKIP_NH_OIF;
+				goto out;
+			}
+		}
+	}
+
+	if (fl->flowi_iif) {
+		dev = dev_get_by_index_rcu(net, fl->flowi_iif);
+		if (dev) {
+			ifindex = l3mdev_master_ifindex_rcu(dev);
+			if (ifindex) {
+				fl->flowi_iif = ifindex;
+				fl->flowi_flags |= FLOWI_FLAG_SKIP_NH_OIF;
+			}
+		}
+	}
+
+out:
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(l3mdev_update_flow);