[PATCH net] wireguard: remove peer cache in netns_pre_exit

[Hangbin Liu <liuhangbin@gmail.com>]

wg_peer_remove_all() will put peer's refcount and clear peer's dst cache
if no ref hold. Currently, it was only called in wg_destruct().

When delete a netns with wg interface in side, the wg_netns_pre_exit() is
called first. Later in netdev_run_todo() the function will be hung at
netdev_wait_allrefs(dev) as dev->priv_destructor(dev) runs later, the
peer's dst cache could not be cleared and there is still a reference on
the device. This could cause kernel errors like:

unregister_netdevice: waiting for wg0 to become free. Usage count = 2
(if remove the veth interface in netns first)
or
unregister_netdevice: waiting for veth1 to become free. Usage count = 2
(if not remove veth interface first)

Fix it by removing peer cache in netns_pre_exit.

Also add a test in netns.sh for this issue.

Reported-by: Xiumei Mu <xmu@redhat.com>
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
---
 drivers/net/wireguard/device.c             |  1 +
 tools/testing/selftests/wireguard/netns.sh | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/net/wireguard/device.c b/drivers/net/wireguard/device.c
index 551ddaaaf540..c370854c76eb 100644
--- a/drivers/net/wireguard/device.c
+++ b/drivers/net/wireguard/device.c
@@ -407,6 +407,7 @@ static void wg_netns_pre_exit(struct net *net)
 			mutex_lock(&wg->device_update_lock);
 			rcu_assign_pointer(wg->creating_net, NULL);
 			wg_socket_reinit(wg, NULL, NULL);
+			wg_peer_remove_all(wg);
 			mutex_unlock(&wg->device_update_lock);
 		}
 	}
diff --git a/tools/testing/selftests/wireguard/netns.sh b/tools/testing/selftests/wireguard/netns.sh
index ebc4ee0fe179..d94c2c887bcd 100755
--- a/tools/testing/selftests/wireguard/netns.sh
+++ b/tools/testing/selftests/wireguard/netns.sh
@@ -614,6 +614,24 @@ ip1 link add wg1 type wireguard
 ip2 link add wg2 type wireguard
 ip1 link set wg1 netns $netns2
 ip2 link set wg2 netns $netns1
+
+ip1 link add dev wg0 type wireguard
+ip2 link add dev wg0 type wireguard
+configure_peers
+ip1 link add veth1 type veth peer name veth2
+ip1 link set veth2 netns $netns2
+ip1 addr add fd00:aa::1/64 dev veth1
+ip2 addr add fd00:aa::2/64 dev veth2
+ip1 link set veth1 up
+ip2 link set veth2 up
+waitiface $netns1 veth1
+waitiface $netns2 veth2
+ip1 -6 route add default dev veth1 via fd00:aa::2
+ip2 -6 route add default dev veth2 via fd00:aa::1
+n1 wg set wg0 peer "$pub2" endpoint [fd00:aa::2]:2
+n2 wg set wg0 peer "$pub1" endpoint [fd00:aa::1]:1
+n1 ping6 -c 1 fd00::2
+
 pp ip netns delete $netns1
 pp ip netns delete $netns2
 pp ip netns add $netns1
-- 
2.31.1