[PATCH v2] wireguard: device: clear keys on VM fork

["Jason A. Donenfeld" <Jason@zx2c4.com>]

When a virtual machine forks, it's important that WireGuard clear
existing sessions so that different plaintexts are not transmitted using
the same key+nonce, which can result in catastrophic cryptographic
failure. To accomplish this, we simply hook into the newly added vmfork
notifier.

As a bonus, it turns out that, like the vmfork registration function,
the PM registration function is stubbed out when CONFIG_PM_SLEEP is not
set, so we can actually just remove the maze of ifdefs, which makes it
really quite clean to support both notifiers at once.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
Fundamentally the same as v1, but just refactored into its own function
to be less hacky. Meant to post this 10 days ago as it's been sitting in
my tree being tested like this for a while now; this is what I've got
queued up for 5.18, so posting to the list for completeness.

 drivers/net/wireguard/device.c | 38 ++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/drivers/net/wireguard/device.c b/drivers/net/wireguard/device.c
index a46067c38bf5..0fad1331303c 100644
--- a/drivers/net/wireguard/device.c
+++ b/drivers/net/wireguard/device.c
@@ -59,9 +59,7 @@ static int wg_open(struct net_device *dev)
 	return ret;
 }
 
-#ifdef CONFIG_PM_SLEEP
-static int wg_pm_notification(struct notifier_block *nb, unsigned long action,
-			      void *data)
+static int wg_pm_notification(struct notifier_block *nb, unsigned long action, void *data)
 {
 	struct wg_device *wg;
 	struct wg_peer *peer;
@@ -92,7 +90,24 @@ static int wg_pm_notification(struct notifier_block *nb, unsigned long action,
 }
 
 static struct notifier_block pm_notifier = { .notifier_call = wg_pm_notification };
-#endif
+
+static int wg_vm_notification(struct notifier_block *nb, unsigned long action, void *data)
+{
+	struct wg_device *wg;
+	struct wg_peer *peer;
+
+	rtnl_lock();
+	list_for_each_entry(wg, &device_list, device_list) {
+		mutex_lock(&wg->device_update_lock);
+		list_for_each_entry(peer, &wg->peer_list, peer_list)
+			wg_noise_expire_current_peer_keypairs(peer);
+		mutex_unlock(&wg->device_update_lock);
+	}
+	rtnl_unlock();
+	return 0;
+}
+
+static struct notifier_block vm_notifier = { .notifier_call = wg_vm_notification };
 
 static int wg_stop(struct net_device *dev)
 {
@@ -424,16 +439,18 @@ int __init wg_device_init(void)
 {
 	int ret;
 
-#ifdef CONFIG_PM_SLEEP
 	ret = register_pm_notifier(&pm_notifier);
 	if (ret)
 		return ret;
-#endif
 
-	ret = register_pernet_device(&pernet_ops);
+	ret = register_random_vmfork_notifier(&vm_notifier);
 	if (ret)
 		goto error_pm;
 
+	ret = register_pernet_device(&pernet_ops);
+	if (ret)
+		goto error_vm;
+
 	ret = rtnl_link_register(&link_ops);
 	if (ret)
 		goto error_pernet;
@@ -442,10 +459,10 @@ int __init wg_device_init(void)
 
 error_pernet:
 	unregister_pernet_device(&pernet_ops);
+error_vm:
+	unregister_random_vmfork_notifier(&vm_notifier);
 error_pm:
-#ifdef CONFIG_PM_SLEEP
 	unregister_pm_notifier(&pm_notifier);
-#endif
 	return ret;
 }
 
@@ -453,8 +470,7 @@ void wg_device_uninit(void)
 {
 	rtnl_link_unregister(&link_ops);
 	unregister_pernet_device(&pernet_ops);
-#ifdef CONFIG_PM_SLEEP
+	unregister_random_vmfork_notifier(&vm_notifier);
 	unregister_pm_notifier(&pm_notifier);
-#endif
 	rcu_barrier();
 }
-- 
2.35.1