net: rmnet: use upper/lower device infrastructure

netdev_upper_dev_link() is useful to manage lower/upper interfaces.
And this function internally validates looping, maximum depth.
All or most virtual interfaces that could have a real interface
(e.g. macsec, macvlan, ipvlan etc.) use lower/upper infrastructure.

Test commands:
    modprobe rmnet
    ip link add dummy0 type dummy
    ip link add rmnet1 link dummy0 type rmnet mux_id 1
    for i in {2..100}
    do
        let A=$i-1
        ip link add rmnet$i link rmnet$A type rmnet mux_id $i
    done
    ip link del dummy0

The purpose of the test commands is to make stack overflow.

Splat looks like:
[   52.411438][ T1395] BUG: KASAN: slab-out-of-bounds in find_busiest_group+0x27e/0x2c00
[   52.413218][ T1395] Write of size 64 at addr ffff8880c774bde0 by task ip/1395
[   52.414841][ T1395]
[   52.430720][ T1395] CPU: 1 PID: 1395 Comm: ip Not tainted 5.6.0-rc1+ #447
[   52.496511][ T1395] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[   52.513597][ T1395] Call Trace:
[   52.546516][ T1395]
[   52.558773][ T1395] Allocated by task 3171537984:
[   52.588290][ T1395] BUG: unable to handle page fault for address: ffffffffb999e260
[   52.589311][ T1395] #PF: supervisor read access in kernel mode
[   52.590529][ T1395] #PF: error_code(0x0000) - not-present page
[   52.591374][ T1395] PGD d6818067 P4D d6818067 PUD d6819063 PMD 0
[   52.592288][ T1395] Thread overran stack, or stack corrupted
[   52.604980][ T1395] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
[   52.605856][ T1395] CPU: 1 PID: 1395 Comm: ip Not tainted 5.6.0-rc1+ #447
[   52.611764][ T1395] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[   52.621520][ T1395] RIP: 0010:stack_depot_fetch+0x10/0x30
[   52.622296][ T1395] Code: ff e9 f9 fe ff ff 48 89 df e8 9c 1d 91 ff e9 ca fe ff ff cc cc cc cc cc cc cc 89 f8 0
[   52.627887][ T1395] RSP: 0018:ffff8880c774bb60 EFLAGS: 00010006
[   52.628735][ T1395] RAX: 00000000001f8880 RBX: ffff8880c774d140 RCX: 0000000000000000
[   52.631773][ T1395] RDX: 000000000000001d RSI: ffff8880c774bb68 RDI: 0000000000003ff0
[   52.649584][ T1395] RBP: ffffea00031dd200 R08: ffffed101b43e403 R09: ffffed101b43e403
[   52.674857][ T1395] R10: 0000000000000001 R11: ffffed101b43e402 R12: ffff8880d900e5c0
[   52.678257][ T1395] R13: ffff8880c774c000 R14: 0000000000000000 R15: dffffc0000000000
[   52.694541][ T1395] FS:  00007fe867f6e0c0(0000) GS:ffff8880da000000(0000) knlGS:0000000000000000
[   52.764039][ T1395] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   52.815008][ T1395] CR2: ffffffffb999e260 CR3: 00000000c26aa005 CR4: 00000000000606e0
[   52.862312][ T1395] Call Trace:
[   52.887133][ T1395] Modules linked in: dummy rmnet veth openvswitch nsh nf_conncount nf_nat nf_conntrack nf_dex
[   52.936749][ T1395] CR2: ffffffffb999e260
[   52.965695][ T1395] ---[ end trace 7e32ca99482dbb31 ]---
[   52.966556][ T1395] RIP: 0010:stack_depot_fetch+0x10/0x30
[   52.971083][ T1395] Code: ff e9 f9 fe ff ff 48 89 df e8 9c 1d 91 ff e9 ca fe ff ff cc cc cc cc cc cc cc 89 f8 0
[   53.003650][ T1395] RSP: 0018:ffff8880c774bb60 EFLAGS: 00010006
[   53.043183][ T1395] RAX: 00000000001f8880 RBX: ffff8880c774d140 RCX: 0000000000000000
[   53.076480][ T1395] RDX: 000000000000001d RSI: ffff8880c774bb68 RDI: 0000000000003ff0
[   53.093858][ T1395] RBP: ffffea00031dd200 R08: ffffed101b43e403 R09: ffffed101b43e403
[   53.112795][ T1395] R10: 0000000000000001 R11: ffffed101b43e402 R12: ffff8880d900e5c0
[   53.139837][ T1395] R13: ffff8880c774c000 R14: 0000000000000000 R15: dffffc0000000000
[   53.141500][ T1395] FS:  00007fe867f6e0c0(0000) GS:ffff8880da000000(0000) knlGS:0000000000000000
[   53.143343][ T1395] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   53.152007][ T1395] CR2: ffffffffb999e260 CR3: 00000000c26aa005 CR4: 00000000000606e0
[   53.156459][ T1395] Kernel panic - not syncing: Fatal exception
[   54.213570][ T1395] Shutting down cpus with NMI
[   54.354112][ T1395] Kernel Offset: 0x33000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0x)
[   54.355687][ T1395] Rebooting in 5 seconds..

Fixes: b37f78f2 ("net: qualcomm: rmnet: Fix crash on real dev unregistration")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c

@@ -61,9 +61,6 @@ static int rmnet_unregister_real_device(struct net_device *real_dev,
 
 	kfree(port);
 
-	/* release reference on real_dev */
-	dev_put(real_dev);
-
 	netdev_dbg(real_dev, "Removed from rmnet\n");
 	return 0;
 }
@@ -89,9 +86,6 @@ static int rmnet_register_real_device(struct net_device *real_dev)
 		return -EBUSY;
 	}
 
-	/* hold on to real dev for MAP data */
-	dev_hold(real_dev);
-
 	for (entry = 0; entry < RMNET_MAX_LOGICAL_EP; entry++)
 		INIT_HLIST_HEAD(&port->muxed_ep[entry]);
 
@@ -162,6 +156,10 @@ static int rmnet_newlink(struct net *src_net, struct net_device *dev,
 	if (err)
 		goto err1;
 
+	err = netdev_upper_dev_link(real_dev, dev, extack);
+	if (err < 0)
+		goto err2;
+
 	port->rmnet_mode = mode;
 
 	hlist_add_head_rcu(&ep->hlnode, &port->muxed_ep[mux_id]);
@@ -178,6 +176,8 @@ static int rmnet_newlink(struct net *src_net, struct net_device *dev,
 
 	return 0;
 
+err2:
+	unregister_netdevice(dev);
 err1:
 	rmnet_unregister_real_device(real_dev, port);
 err0:
@@ -209,33 +209,30 @@ static void rmnet_dellink(struct net_device *dev, struct list_head *head)
 		rmnet_vnd_dellink(mux_id, port, ep);
 		kfree(ep);
 	}
+	netdev_upper_dev_unlink(real_dev, dev);
 	rmnet_unregister_real_device(real_dev, port);
 
 	unregister_netdevice_queue(dev, head);
 }
 
-static void rmnet_force_unassociate_device(struct net_device *dev)
+static void rmnet_force_unassociate_device(struct net_device *real_dev)
 {
-	struct net_device *real_dev = dev;
 	struct hlist_node *tmp_ep;
 	struct rmnet_endpoint *ep;
 	struct rmnet_port *port;
 	unsigned long bkt_ep;
 	LIST_HEAD(list);
 
-	if (!rmnet_is_real_dev_registered(real_dev))
-		return;
-
 	ASSERT_RTNL();
 
-	port = rmnet_get_port_rtnl(dev);
+	port = rmnet_get_port_rtnl(real_dev);
 
-	rmnet_unregister_bridge(dev, port);
+	rmnet_unregister_bridge(real_dev, port);
 
 	hash_for_each_safe(port->muxed_ep, bkt_ep, tmp_ep, ep, hlnode) {
+		netdev_upper_dev_unlink(real_dev, ep->egress_dev);
 		unregister_netdevice_queue(ep->egress_dev, &list);
 		rmnet_vnd_dellink(ep->mux_id, port, ep);
-
 		hlist_del_init_rcu(&ep->hlnode);
 		kfree(ep);
 	}
@@ -248,15 +245,15 @@ static void rmnet_force_unassociate_device(struct net_device *dev)
 static int rmnet_config_notify_cb(struct notifier_block *nb,
 				  unsigned long event, void *data)
 {
-	struct net_device *dev = netdev_notifier_info_to_dev(data);
+	struct net_device *real_dev = netdev_notifier_info_to_dev(data);
 
-	if (!dev)
+	if (!rmnet_is_real_dev_registered(real_dev))
 		return NOTIFY_DONE;
 
 	switch (event) {
 	case NETDEV_UNREGISTER:
-		netdev_dbg(dev, "Kernel unregister\n");
-		rmnet_force_unassociate_device(dev);
+		netdev_dbg(real_dev, "Kernel unregister\n");
+		rmnet_force_unassociate_device(real_dev);
 		break;
 
 	default:
@@ -477,8 +474,8 @@ static int __init rmnet_init(void)
 
 static void __exit rmnet_exit(void)
 {
-	unregister_netdevice_notifier(&rmnet_dev_notifier);
 	rtnl_link_unregister(&rmnet_link_ops);
+	unregister_netdevice_notifier(&rmnet_dev_notifier);
 }
 
 module_init(rmnet_init)