wireguard: device: clear keys on VM fork

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>

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();
 }