hsr: avoid to create proc file after unregister

When an interface is being deleted, "/proc/net/dev_snmp6/<interface name>"
is deleted.
The function for this is addrconf_ifdown() in the addrconf_notify() and
it is called by notification, which is NETDEV_UNREGISTER.
But, if NETDEV_CHANGEMTU is triggered after NETDEV_UNREGISTER,
this proc file will be created again.
This recreated proc file will be deleted by netdev_wati_allrefs().
Before netdev_wait_allrefs() is called, creating a new HSR interface
routine can be executed and It tries to create a proc file but it will
find an un-deleted proc file.
At this point, it warns about it.

To avoid this situation, it can use ->dellink() instead of
->ndo_uninit() to release resources because ->dellink() is called
before NETDEV_UNREGISTER.
So, a proc file will not be recreated.

Test commands
    ip link add dummy0 type dummy
    ip link add dummy1 type dummy
    ip link set dummy0 mtu 1300

    #SHELL1
    while :
    do
        ip link add hsr0 type hsr slave1 dummy0 slave2 dummy1
    done

    #SHELL2
    while :
    do
        ip link del hsr0
    done

Splat looks like:
[ 9888.980852][ T2752] proc_dir_entry 'dev_snmp6/hsr0' already registered
[ 9888.981797][    C2] WARNING: CPU: 2 PID: 2752 at fs/proc/generic.c:372 proc_register+0x2d5/0x430
[ 9888.981798][    C2] Modules linked in: hsr dummy veth openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6x
[ 9888.981814][    C2] CPU: 2 PID: 2752 Comm: ip Tainted: G        W         5.8.0-rc1+ #616
[ 9888.981815][    C2] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 9888.981816][    C2] RIP: 0010:proc_register+0x2d5/0x430
[ 9888.981818][    C2] Code: fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 65 01 00 00 49 8b b5 e0 00 00 00 48 89 ea 40
[ 9888.981819][    C2] RSP: 0018:ffff8880628dedf0 EFLAGS: 00010286
[ 9888.981821][    C2] RAX: dffffc0000000008 RBX: ffff888028c69170 RCX: ffffffffaae09a62
[ 9888.981822][    C2] RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff88806c9f75ac
[ 9888.981823][    C2] RBP: ffff888028c693f4 R08: ffffed100d9401bd R09: ffffed100d9401bd
[ 9888.981824][    C2] R10: ffffffffaddf406f R11: 0000000000000001 R12: ffff888028c69308
[ 9888.981825][    C2] R13: ffff8880663584c8 R14: dffffc0000000000 R15: ffffed100518d27e
[ 9888.981827][    C2] FS:  00007f3876b3b0c0(0000) GS:ffff88806c800000(0000) knlGS:0000000000000000
[ 9888.981828][    C2] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9888.981829][    C2] CR2: 00007f387601a8c0 CR3: 000000004101a002 CR4: 00000000000606e0
[ 9888.981830][    C2] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9888.981831][    C2] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9888.981832][    C2] Call Trace:
[ 9888.981833][    C2]  ? snmp6_seq_show+0x180/0x180
[ 9888.981834][    C2]  proc_create_single_data+0x7c/0xa0
[ 9888.981835][    C2]  snmp6_register_dev+0xb0/0x130
[ 9888.981836][    C2]  ipv6_add_dev+0x4b7/0xf60
[ 9888.981837][    C2]  addrconf_notify+0x684/0x1ca0
[ 9888.981838][    C2]  ? __mutex_unlock_slowpath+0xd0/0x670
[ 9888.981839][    C2]  ? kasan_unpoison_shadow+0x30/0x40
[ 9888.981840][    C2]  ? wait_for_completion+0x250/0x250
[ 9888.981841][    C2]  ? inet6_ifinfo_notify+0x100/0x100
[ 9888.981842][    C2]  ? dropmon_net_event+0x227/0x410
[ 9888.981843][    C2]  ? notifier_call_chain+0x90/0x160
[ 9888.981844][    C2]  ? inet6_ifinfo_notify+0x100/0x100
[ 9888.981845][    C2]  notifier_call_chain+0x90/0x160
[ 9888.981846][    C2]  register_netdevice+0xbe5/0x1070
[ ... ]

Reported-by: syzbot+1d51c8b74efa4c44adeb@syzkaller.appspotmail.com
Fixes: e0a4b997 ("hsr: use upper/lower device infrastructure")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/hsr/hsr_device.c

@@ -339,7 +339,7 @@ static void hsr_announce(struct timer_list *t)
 	rcu_read_unlock();
 }
 
-static void hsr_del_ports(struct hsr_priv *hsr)
+void hsr_del_ports(struct hsr_priv *hsr)
 {
 	struct hsr_port *port;
 
@@ -356,31 +356,12 @@ static void hsr_del_ports(struct hsr_priv *hsr)
 		hsr_del_port(port);
 }
 
-/* This has to be called after all the readers are gone.
- * Otherwise we would have to check the return value of
- * hsr_port_get_hsr().
- */
-static void hsr_dev_destroy(struct net_device *hsr_dev)
-{
-	struct hsr_priv *hsr = netdev_priv(hsr_dev);
-
-	hsr_debugfs_term(hsr);
-	hsr_del_ports(hsr);
-
-	del_timer_sync(&hsr->prune_timer);
-	del_timer_sync(&hsr->announce_timer);
-
-	hsr_del_self_node(hsr);
-	hsr_del_nodes(&hsr->node_db);
-}
-
 static const struct net_device_ops hsr_device_ops = {
 	.ndo_change_mtu = hsr_dev_change_mtu,
 	.ndo_open = hsr_dev_open,
 	.ndo_stop = hsr_dev_close,
 	.ndo_start_xmit = hsr_dev_xmit,
 	.ndo_fix_features = hsr_fix_features,
-	.ndo_uninit = hsr_dev_destroy,
 };
 
 static struct device_type hsr_type = {

net/hsr/hsr_device.h

@@ -11,6 +11,7 @@
 #include <linux/netdevice.h>
 #include "hsr_main.h"
 
+void hsr_del_ports(struct hsr_priv *hsr);
 void hsr_dev_setup(struct net_device *dev);
 int hsr_dev_finalize(struct net_device *hsr_dev, struct net_device *slave[2],
 		     unsigned char multicast_spec, u8 protocol_version,
@@ -18,5 +19,4 @@ int hsr_dev_finalize(struct net_device *hsr_dev, struct net_device *slave[2],
 void hsr_check_carrier_and_operstate(struct hsr_priv *hsr);
 bool is_hsr_master(struct net_device *dev);
 int hsr_get_max_mtu(struct hsr_priv *hsr);
-
 #endif /* __HSR_DEVICE_H */

net/hsr/hsr_main.c

@@ -6,6 +6,7 @@
  */
 
 #include <linux/netdevice.h>
+#include <net/rtnetlink.h>
 #include <linux/rculist.h>
 #include <linux/timer.h>
 #include <linux/etherdevice.h>
@@ -100,8 +101,10 @@ static int hsr_netdev_notify(struct notifier_block *nb, unsigned long event,
 			master = hsr_port_get_hsr(port->hsr, HSR_PT_MASTER);
 			hsr_del_port(port);
 			if (hsr_slave_empty(master->hsr)) {
-				unregister_netdevice_queue(master->dev,
-							   &list_kill);
+				const struct rtnl_link_ops *ops;
+
+				ops = master->dev->rtnl_link_ops;
+				ops->dellink(master->dev, &list_kill);
 				unregister_netdevice_many(&list_kill);
 			}
 		}
@@ -144,9 +147,9 @@ static int __init hsr_init(void)
 
 static void __exit hsr_exit(void)
 {
-	unregister_netdevice_notifier(&hsr_nb);
 	hsr_netlink_exit();
 	hsr_debugfs_remove_root();
+	unregister_netdevice_notifier(&hsr_nb);
 }
 
 module_init(hsr_init);

net/hsr/hsr_netlink.c

@@ -83,6 +83,22 @@ static int hsr_newlink(struct net *src_net, struct net_device *dev,
 	return hsr_dev_finalize(dev, link, multicast_spec, hsr_version, extack);
 }
 
+static void hsr_dellink(struct net_device *dev, struct list_head *head)
+{
+	struct hsr_priv *hsr = netdev_priv(dev);
+
+	del_timer_sync(&hsr->prune_timer);
+	del_timer_sync(&hsr->announce_timer);
+
+	hsr_debugfs_term(hsr);
+	hsr_del_ports(hsr);
+
+	hsr_del_self_node(hsr);
+	hsr_del_nodes(&hsr->node_db);
+
+	unregister_netdevice_queue(dev, head);
+}
+
 static int hsr_fill_info(struct sk_buff *skb, const struct net_device *dev)
 {
 	struct hsr_priv *hsr = netdev_priv(dev);
@@ -118,6 +134,7 @@ static struct rtnl_link_ops hsr_link_ops __read_mostly = {
 	.priv_size	= sizeof(struct hsr_priv),
 	.setup		= hsr_dev_setup,
 	.newlink	= hsr_newlink,
+	.dellink	= hsr_dellink,
 	.fill_info	= hsr_fill_info,
 };