From: David Ahern dsahern@kernel.org
[ Upstream commit 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 ]
Kfir reported that pmtu exceptions are not created properly for deployments where multipath routes use the same device.
After some digging I see 2 compounding problems: 1. ip_route_output_key_hash_rcu is updating the flowi4_oif *after* the route lookup. This is the second use case where this has been a problem (the first is related to use of vti devices with VRF). I can not find any reason for the oif to be changed after the lookup; the code goes back to the start of git. It does not seem logical so remove it.
2. fib_lookups for exceptions do not call fib_select_path to handle multipath route selection based on the hash.
The end result is that the fib_lookup used to add the exception always creates it based using the first leg of the route.
An example topology showing the problem:
| host1 +------+ | eth0 | .209 +------+ | +------+ switch | br0 | +------+ | +---------+---------+ | host2 | host3 +------+ +------+ | eth0 | .250 | eth0 | 192.168.252.252 +------+ +------+
+-----+ +-----+ | vti | .2 | vti | 192.168.247.3 +-----+ +-----+ \ / ================================= tunnels 192.168.247.1/24
for h in host1 host2 host3; do ip netns add ${h} ip -netns ${h} link set lo up ip netns exec ${h} sysctl -wq net.ipv4.ip_forward=1 done
ip netns add switch ip -netns switch li set lo up ip -netns switch link add br0 type bridge stp 0 ip -netns switch link set br0 up
for n in 1 2 3; do ip -netns switch link add eth-sw type veth peer name eth-h${n} ip -netns switch li set eth-h${n} master br0 up ip -netns switch li set eth-sw netns host${n} name eth0 done
ip -netns host1 addr add 192.168.252.209/24 dev eth0 ip -netns host1 link set dev eth0 up ip -netns host1 route add 192.168.247.0/24 \ nexthop via 192.168.252.250 dev eth0 nexthop via 192.168.252.252 dev eth0
ip -netns host2 addr add 192.168.252.250/24 dev eth0 ip -netns host2 link set dev eth0 up
ip -netns host2 addr add 192.168.252.252/24 dev eth0 ip -netns host3 link set dev eth0 up
ip netns add tunnel ip -netns tunnel li set lo up ip -netns tunnel li add br0 type bridge ip -netns tunnel li set br0 up for n in $(seq 11 20); do ip -netns tunnel addr add dev br0 192.168.247.${n}/24 done
for n in 2 3 do ip -netns tunnel link add vti${n} type veth peer name eth${n} ip -netns tunnel link set eth${n} mtu 1360 master br0 up ip -netns tunnel link set vti${n} netns host${n} mtu 1360 up ip -netns host${n} addr add dev vti${n} 192.168.247.${n}/24 done ip -netns tunnel ro add default nexthop via 192.168.247.2 nexthop via 192.168.247.3
ip netns exec host1 ping -M do -s 1400 -c3 -I 192.168.252.209 192.168.247.11 ip netns exec host1 ping -M do -s 1400 -c3 -I 192.168.252.209 192.168.247.15 ip -netns host1 ro ls cache
Before this patch the cache always shows exceptions against the first leg in the multipath route; 192.168.252.250 per this example. Since the hash has an initial random seed, you may need to vary the final octet more than what is listed. In my tests, using addresses between 11 and 19 usually found 1 that used both legs.
With this patch, the cache will have exceptions for both legs.
Fixes: 4895c771c7f0 ("ipv4: Add FIB nexthop exceptions") Reported-by: Kfir Itzhak mastertheknife@gmail.com Signed-off-by: David Ahern dsahern@kernel.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/route.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
--- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -794,6 +794,8 @@ static void __ip_do_redirect(struct rtab if (fib_lookup(net, fl4, &res, 0) == 0) { struct fib_nh *nh = &FIB_RES_NH(res);
+ fib_select_path(net, &res, fl4, skb); + nh = &FIB_RES_NH(res); update_or_create_fnhe(nh, fl4->daddr, new_gw, 0, false, jiffies + ip_rt_gc_timeout); @@ -1010,6 +1012,7 @@ out: kfree_skb(skb); static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu) { struct dst_entry *dst = &rt->dst; + struct net *net = dev_net(dst->dev); u32 old_mtu = ipv4_mtu(dst); struct fib_result res; bool lock = false; @@ -1030,9 +1033,11 @@ static void __ip_rt_update_pmtu(struct r return;
rcu_read_lock(); - if (fib_lookup(dev_net(dst->dev), fl4, &res, 0) == 0) { - struct fib_nh *nh = &FIB_RES_NH(res); + if (fib_lookup(net, fl4, &res, 0) == 0) { + struct fib_nh *nh;
+ fib_select_path(net, &res, fl4, NULL); + nh = &FIB_RES_NH(res); update_or_create_fnhe(nh, fl4->daddr, 0, mtu, lock, jiffies + ip_rt_mtu_expires); } @@ -2505,8 +2510,6 @@ struct rtable *ip_route_output_key_hash_ fib_select_path(net, res, fl4, skb);
dev_out = FIB_RES_DEV(*res); - fl4->flowi4_oif = dev_out->ifindex; -
make_route: rth = __mkroute_output(res, fl4, orig_oif, dev_out, flags);