net: l3mdev: Allow send on enslaved interface

Allow udp and raw sockets to send by oif that is an enslaved interface
versus the l3mdev/VRF device. For example, this allows BFD to use ifindex
from IP_PKTINFO on a receive to send a response without the need to
convert to the VRF index. It also allows ping and ping6 to work when
specifying an enslaved interface (e.g., ping -I swp1 <ip>) which is
a natural use case.

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

drivers/net/vrf.c

@@ -648,6 +648,8 @@ static int vrf_get_saddr(struct net_device *dev, struct flowi4 *fl4)
 
 	fl4->flowi4_flags |= FLOWI_FLAG_SKIP_NH_OIF;
 	fl4->flowi4_iif = LOOPBACK_IFINDEX;
+	/* make sure oif is set to VRF device for lookup */
+	fl4->flowi4_oif = dev->ifindex;
 	fl4->flowi4_tos = tos & IPTOS_RT_MASK;
 	fl4->flowi4_scope = ((tos & RTO_ONLINK) ?
 			     RT_SCOPE_LINK : RT_SCOPE_UNIVERSE);

net/ipv4/route.c

@@ -2146,6 +2146,7 @@ struct rtable *__ip_route_output_key_hash(struct net *net, struct flowi4 *fl4,
 	unsigned int flags = 0;
 	struct fib_result res;
 	struct rtable *rth;
+	int master_idx;
 	int orig_oif;
 	int err = -ENETUNREACH;
 
@@ -2155,6 +2156,9 @@ struct rtable *__ip_route_output_key_hash(struct net *net, struct flowi4 *fl4,
 
 	orig_oif = fl4->flowi4_oif;
 
+	master_idx = l3mdev_master_ifindex_by_index(net, fl4->flowi4_oif);
+	if (master_idx)
+		fl4->flowi4_oif = master_idx;
 	fl4->flowi4_iif = LOOPBACK_IFINDEX;
 	fl4->flowi4_tos = tos & IPTOS_RT_MASK;
 	fl4->flowi4_scope = ((tos & RTO_ONLINK) ?

net/l3mdev/l3mdev.c

@@ -112,12 +112,18 @@ struct dst_entry *l3mdev_get_rt6_dst(struct net *net,
 	struct dst_entry *dst = NULL;
 	struct net_device *dev;
 
-	dev = dev_get_by_index(net, fl6->flowi6_oif);
-	if (dev) {
-		if (netif_is_l3_master(dev) &&
+	if (fl6->flowi6_oif) {
+		rcu_read_lock();
+
+		dev = dev_get_by_index_rcu(net, fl6->flowi6_oif);
+		if (dev && netif_is_l3_slave(dev))
+			dev = netdev_master_upper_dev_get_rcu(dev);
+
+		if (dev && netif_is_l3_master(dev) &&
 		    dev->l3mdev_ops->l3mdev_get_rt6_dst)
 			dst = dev->l3mdev_ops->l3mdev_get_rt6_dst(dev, fl6);
-		dev_put(dev);
+
+		rcu_read_unlock();
 	}
 
 	return dst;
@@ -141,6 +147,9 @@ int l3mdev_get_saddr(struct net *net, int ifindex, struct flowi4 *fl4)
 		rcu_read_lock();
 
 		dev = dev_get_by_index_rcu(net, ifindex);
+		if (dev && netif_is_l3_slave(dev))
+			dev = netdev_master_upper_dev_get_rcu(dev);
+
 		if (dev && netif_is_l3_master(dev) &&
 		    dev->l3mdev_ops->l3mdev_get_saddr)
 			rc = dev->l3mdev_ops->l3mdev_get_saddr(dev, fl4);