psp: add a new netdev event for dev unregister

Add a new netdev event for dev unregister and handle the removal of this
dev from psp->assoc_dev_list, upon the first dev-assoc operation.

Signed-off-by: Wei Wang <weibunny@fb.com>
Reviewed-by: Daniel Zahka <daniel.zahka@gmail.com>
Link: https://patch.msgid.link/20260608233118.2694144-4-weibunny.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/specs/psp.yaml

@@ -331,7 +331,7 @@ operations:
             - nsid
         reply:
           attributes: []
-        pre: psp-device-get-locked
+        pre: psp-device-get-locked-dev-assoc
         post: psp-device-unlock
     -
       name: dev-disassoc

net/psp/psp-nl-gen.c

@@ -135,7 +135,7 @@ static const struct genl_split_ops psp_nl_ops[] = {
 	},
 	{
 		.cmd		= PSP_CMD_DEV_ASSOC,
-		.pre_doit	= psp_device_get_locked,
+		.pre_doit	= psp_device_get_locked_dev_assoc,
 		.doit		= psp_nl_dev_assoc_doit,
 		.post_doit	= psp_device_unlock,
 		.policy		= psp_dev_assoc_nl_policy,

net/psp/psp-nl-gen.h

@@ -21,6 +21,9 @@ int psp_device_get_locked_admin(const struct genl_split_ops *ops,
 				struct sk_buff *skb, struct genl_info *info);
 int psp_assoc_device_get_locked(const struct genl_split_ops *ops,
 				struct sk_buff *skb, struct genl_info *info);
+int psp_device_get_locked_dev_assoc(const struct genl_split_ops *ops,
+				    struct sk_buff *skb,
+				    struct genl_info *info);
 void
 psp_device_unlock(const struct genl_split_ops *ops, struct sk_buff *skb,
 		  struct genl_info *info);

net/psp/psp.h

@@ -16,6 +16,7 @@ extern struct mutex psp_devs_lock;
 void psp_dev_free(struct psp_dev *psd);
 int psp_dev_check_access(struct psp_dev *psd, struct net *net, bool admin);
 bool psp_has_assoc_dev_in_ns(struct psp_dev *psd, struct net *net);
+int psp_attach_netdev_notifier(void);
 
 void psp_nl_notify_dev(struct psp_dev *psd, u32 cmd);
 

net/psp/psp_main.c

@@ -405,6 +405,81 @@ int psp_dev_rcv(struct sk_buff *skb, u16 dev_id, u8 generation, bool strip_icv)
 }
 EXPORT_SYMBOL(psp_dev_rcv);
 
+static void psp_dev_disassoc_one(struct psp_dev *psd, struct net_device *dev)
+{
+	struct psp_assoc_dev *entry;
+
+	list_for_each_entry(entry, &psd->assoc_dev_list, dev_list) {
+		if (entry->assoc_dev == dev) {
+			list_del(&entry->dev_list);
+			psd->assoc_dev_cnt--;
+			rcu_assign_pointer(entry->assoc_dev->psp_dev, NULL);
+			netdev_put(entry->assoc_dev, &entry->dev_tracker);
+			kfree(entry);
+			return;
+		}
+	}
+}
+
+static int psp_netdev_event(struct notifier_block *nb, unsigned long event,
+			    void *ptr)
+{
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+	struct psp_dev *psd;
+
+	if (event != NETDEV_UNREGISTER)
+		return NOTIFY_DONE;
+
+	rcu_read_lock();
+	psd = rcu_dereference(dev->psp_dev);
+	if (psd && psp_dev_tryget(psd)) {
+		rcu_read_unlock();
+		mutex_lock(&psd->lock);
+		if (psp_dev_is_registered(psd))
+			psp_nl_notify_dev(psd, PSP_CMD_DEV_CHANGE_NTF);
+		psp_dev_disassoc_one(psd, dev);
+		mutex_unlock(&psd->lock);
+		psp_dev_put(psd);
+	} else {
+		rcu_read_unlock();
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block psp_netdev_notifier = {
+	.notifier_call = psp_netdev_event,
+};
+
+static DEFINE_MUTEX(psp_notifier_lock);
+static bool psp_notifier_registered;
+
+/* Register the netdevice notifier when the first device association
+ * is created. In many installations no associations will be created and
+ * the notifier won't be needed.
+ *
+ * Must be called without psd->lock held, due to lock ordering:
+ * rtnl_lock -> psd->lock (the notifier callback runs under rtnl_lock
+ * and takes psd->lock).
+ */
+int psp_attach_netdev_notifier(void)
+{
+	int err = 0;
+
+	if (READ_ONCE(psp_notifier_registered))
+		return 0;
+
+	mutex_lock(&psp_notifier_lock);
+	if (!psp_notifier_registered) {
+		err = register_netdevice_notifier(&psp_netdev_notifier);
+		if (!err)
+			WRITE_ONCE(psp_notifier_registered, true);
+	}
+	mutex_unlock(&psp_notifier_lock);
+
+	return err;
+}
+
 static int __init psp_init(void)
 {
 	mutex_init(&psp_devs_lock);

net/psp/psp_nl.c

@@ -160,6 +160,22 @@ int psp_device_get_locked(const struct genl_split_ops *ops,
 	return __psp_device_get_locked(ops, skb, info, false);
 }
 
+/*
+ * Non-admin version of psp_device_get_locked() + psp_attach_netdev_notifier()
+ * only used for dev-assoc.
+ */
+int psp_device_get_locked_dev_assoc(const struct genl_split_ops *ops,
+				    struct sk_buff *skb, struct genl_info *info)
+{
+	int err;
+
+	err = psp_attach_netdev_notifier();
+	if (err)
+		return err;
+
+	return __psp_device_get_locked(ops, skb, info, false);
+}
+
 static struct net *psp_nl_resolve_assoc_dev_ns(struct psp_dev *psd,
 					       struct genl_info *info)
 {
@@ -518,6 +534,19 @@ int psp_nl_dev_assoc_doit(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	psp_assoc_dev->assoc_dev = assoc_dev;
+
+	/* Check for race with NETDEV_UNREGISTER. The cmpxchg above is a
+	 * full barrier, and the unregister path has synchronize_net()
+	 * between setting NETREG_UNREGISTERING and reading psp_dev in the
+	 * notifier. So at least one side would do the clean-up if we are in
+	 * the middle of unregitering assoc_dev.
+	 * And the clean-up is serialized by psd->lock.
+	 */
+	if (READ_ONCE(assoc_dev->reg_state) != NETREG_REGISTERED) {
+		err = -ENODEV;
+		goto err_clean_ptr;
+	}
+
 	rsp = psp_nl_reply_new(info);
 	if (!rsp) {
 		err = -ENOMEM;