bonding: check error value of register_netdevice() immediately

If register_netdevice() is failed, net_device should not be used
because variables are uninitialized or freed.
So, the routine should be stopped immediately.
But, bond_create() doesn't check return value of register_netdevice()
immediately. That will result in a panic because of using uninitialized
or freed memory.

Test commands:
    modprobe netdev-notifier-error-inject
    echo -22 > /sys/kernel/debug/notifier-error-inject/netdev/\
actions/NETDEV_REGISTER/error
    modprobe bonding max_bonds=3

Splat looks like:
[  375.028492][  T193] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] SMP DEBUG_PAGEALLOC PTI
[  375.033207][  T193] CPU: 2 PID: 193 Comm: kworker/2:2 Not tainted 5.8.0-rc4+ torvalds#645
[  375.036068][  T193] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[  375.039673][  T193] Workqueue: events linkwatch_event
[  375.041557][  T193] RIP: 0010:dev_activate+0x4a/0x340
[  375.043381][  T193] Code: 40 a8 04 0f 85 db 00 00 00 8b 83 08 04 00 00 85 c0 0f 84 0d 01 00 00 31 d2 89 d0 48 8d 04 40 48 c1 e0 07 48 03 83 00 04 00 00 <48> 8b 48 10 f6 41 10 01 75 08 f0 80 a1 a0 01 00 00 fd 48 89 48 08
[  375.050267][  T193] RSP: 0018:ffff9f8facfcfdd8 EFLAGS: 00010202
[  375.052410][  T193] RAX: 6b6b6b6b6b6b6b6b RBX: ffff9f8fae6ea000 RCX: 0000000000000006
[  375.055178][  T193] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9f8fae6ea000
[  375.057762][  T193] RBP: ffff9f8fae6ea000 R08: 0000000000000000 R09: 0000000000000000
[  375.059810][  T193] R10: 0000000000000001 R11: 0000000000000000 R12: ffff9f8facfcfe08
[  375.061892][  T193] R13: ffffffff883587e0 R14: 0000000000000000 R15: ffff9f8fae6ea580
[  375.063931][  T193] FS:  0000000000000000(0000) GS:ffff9f8fbae00000(0000) knlGS:0000000000000000
[  375.066239][  T193] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  375.067841][  T193] CR2: 00007f2f542167a0 CR3: 000000012cee6002 CR4: 00000000003606e0
[  375.069657][  T193] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  375.071471][  T193] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  375.073269][  T193] Call Trace:
[  375.074005][  T193]  linkwatch_do_dev+0x4d/0x50
[  375.075052][  T193]  __linkwatch_run_queue+0x10b/0x200
[  375.076244][  T193]  linkwatch_event+0x21/0x30
[  375.077274][  T193]  process_one_work+0x252/0x600
[  375.078379][  T193]  ? process_one_work+0x600/0x600
[  375.079518][  T193]  worker_thread+0x3c/0x380
[  375.080534][  T193]  ? process_one_work+0x600/0x600
[  375.081668][  T193]  kthread+0x139/0x150
[  375.082567][  T193]  ? kthread_park+0x90/0x90
[  375.083567][  T193]  ret_from_fork+0x22/0x30

Fixes: e826eaf ("bonding: Call netif_carrier_off after register_netdevice")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -5053,15 +5053,19 @@ int bond_create(struct net *net, const char *name)
 	bond_dev->rtnl_link_ops = &bond_link_ops;
 
 	res = register_netdevice(bond_dev);
+	if (res < 0) {
+		free_netdev(bond_dev);
+		rtnl_unlock();
+
+		return res;
+	}
 
 	netif_carrier_off(bond_dev);
 
 	bond_work_init_all(bond);
 
 	rtnl_unlock();
-	if (res < 0)
-		free_netdev(bond_dev);
-	return res;
+	return 0;
 }
 
 static int __net_init bond_net_init(struct net *net)