[PATCH net v4 12/12] virt_wifi: fix refcnt leak in module exit routine

virt_wifi_newlink() calls netdev_upper_dev_link() and it internally
holds reference count of lower interface.

Current code does not release a reference count of the lower interface
when the lower interface is being deleted.
So, reference count leaks occur.

Test commands:
    ip link add dummy0 type dummy
    ip link add vw1 link dummy0 type virt_wifi

Splat looks like:
[  182.001918][ T1333] WARNING: CPU: 0 PID: 1333 at net/core/dev.c:8638 rollback_registered_many+0x75d/0xda0
[  182.002724][ T1333] Modules linked in: virt_wifi cfg80211 dummy veth openvswitch nsh nf_conncount nf_nat nf_conntrack6
[  182.002724][ T1333] CPU: 0 PID: 1333 Comm: ip Not tainted 5.3.0+ #370
[  182.002724][ T1333] RIP: 0010:rollback_registered_many+0x75d/0xda0
[  182.002724][ T1333] Code: 0c 00 00 48 89 de 4c 89 ff e8 6f 5a 04 00 48 89 df e8 c7 26 fd ff 84 c0 0f 84 a5 fd ff ff 40
[  182.002724][ T1333] RSP: 0018:ffff88810900f348 EFLAGS: 00010286
[  182.002724][ T1333] RAX: 0000000000000024 RBX: ffff88811361d700 RCX: 0000000000000000
[  182.002724][ T1333] RDX: 0000000000000024 RSI: 0000000000000008 RDI: ffffed1021201e5f
[  182.002724][ T1333] RBP: ffff88810900f4e0 R08: ffffed1022c3ff71 R09: ffffed1022c3ff71
[  182.002724][ T1333] R10: 0000000000000001 R11: ffffed1022c3ff70 R12: dffffc0000000000
[  182.002724][ T1333] R13: ffff88810900f460 R14: ffff88810900f420 R15: ffff8881075f1940
[  182.002724][ T1333] FS:  00007f77c42240c0(0000) GS:ffff888116000000(0000) knlGS:0000000000000000
[  182.002724][ T1333] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  182.002724][ T1333] CR2: 00007f77c3706240 CR3: 000000011139e000 CR4: 00000000001006f0
[  182.002724][ T1333] Call Trace:
[  182.002724][ T1333]  ? generic_xdp_install+0x310/0x310
[  182.002724][ T1333]  ? check_chain_key+0x236/0x5d0
[  182.002724][ T1333]  ? __nla_validate_parse+0x98/0x1ad0
[  182.002724][ T1333]  unregister_netdevice_many.part.123+0x13/0x1b0
[  182.002724][ T1333]  rtnl_delete_link+0xbc/0x100
[  182.002724][ T1333]  ? rtnl_af_register+0xc0/0xc0
[  182.002724][ T1333]  rtnl_dellink+0x2e7/0x870
[ ... ]

[  192.874736][ T1333] unregister_netdevice: waiting for dummy0 to become free. Usage count = 1

This patch adds notifier routine to delete upper interface before deleting
lower interface.

Fixes: c7cdba31ed8b ("mac80211-next: rtnetlink wifi simulation device")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
---

v4:
 - Add this new patch to fix refcnt leaks in the virt_wifi module

 drivers/net/wireless/virt_wifi.c | 51 ++++++++++++++++++++++++++++++--
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/virt_wifi.c b/drivers/net/wireless/virt_wifi.c
index be92e1220284..aadbacb01c8d 100644
--- a/drivers/net/wireless/virt_wifi.c
+++ b/drivers/net/wireless/virt_wifi.c

@@ -590,6 +590,42 @@ static struct rtnl_link_ops virt_wifi_link_ops = {
 	.priv_size	= sizeof(struct virt_wifi_netdev_priv),
 };
 
+static inline bool netif_is_virt_wifi_dev(const struct net_device *dev)
+{
+	return rcu_access_pointer(dev->rx_handler) == virt_wifi_rx_handler;
+}
+
+static int virt_wifi_event(struct notifier_block *this, unsigned long event,
+			   void *ptr)
+{
+	struct net_device *lower_dev = netdev_notifier_info_to_dev(ptr);
+	struct virt_wifi_netdev_priv *priv;
+	struct net_device *upper_dev;
+	LIST_HEAD(list_kill);
+
+	if (!netif_is_virt_wifi_dev(lower_dev))
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_UNREGISTER:
+		priv = rtnl_dereference(lower_dev->rx_handler_data);
+		if (!priv)
+			return NOTIFY_DONE;
+
+		upper_dev = priv->upperdev;
+
+		upper_dev->rtnl_link_ops->dellink(upper_dev, &list_kill);
+		unregister_netdevice_many(&list_kill);
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block virt_wifi_notifier = {
+	.notifier_call = virt_wifi_event,
+};
+
 /* Acquires and releases the rtnl lock. */
 static int __init virt_wifi_init_module(void)
 {

@@ -598,14 +634,24 @@ static int __init virt_wifi_init_module(void)
 	/* Guaranteed to be locallly-administered and not multicast. */
 	eth_random_addr(fake_router_bssid);
 
+	err = register_netdevice_notifier(&virt_wifi_notifier);
+	if (err)
+		return err;
+
 	common_wiphy = virt_wifi_make_wiphy();
 	if (!common_wiphy)
-		return -ENOMEM;
+		goto notifier;
 
 	err = rtnl_link_register(&virt_wifi_link_ops);
 	if (err)
-		virt_wifi_destroy_wiphy(common_wiphy);
+		goto destroy_wiphy;
 
+	return 0;
+
+destroy_wiphy:
+	virt_wifi_destroy_wiphy(common_wiphy);
+notifier:
+	unregister_netdevice_notifier(&virt_wifi_notifier);
 	return err;
 }
 

@@ -615,6 +661,7 @@ static void __exit virt_wifi_cleanup_module(void)
 	/* Will delete any devices that depend on the wiphy. */
 	rtnl_link_unregister(&virt_wifi_link_ops);
 	virt_wifi_destroy_wiphy(common_wiphy);
+	unregister_netdevice_notifier(&virt_wifi_notifier);
 }
 
 module_init(virt_wifi_init_module);

-- 
2.17.1