net: linkwatch: be more careful about dev->linkwatch_dev_tracker

Apparently a concurrent linkwatch_add_event() could
run while we are in __linkwatch_run_queue().

We need to free dev->linkwatch_dev_tracker tracker
under lweventlist_lock protection to avoid this race.

syzbot report:
[   77.935949][ T3661] reference already released.
[   77.941015][ T3661] allocated in:
[   77.944482][ T3661]  linkwatch_fire_event+0x202/0x260
[   77.950318][ T3661]  netif_carrier_on+0x9c/0x100
[   77.955120][ T3661]  __ieee80211_sta_join_ibss+0xc52/0x1590
[   77.960888][ T3661]  ieee80211_sta_create_ibss.cold+0xd2/0x11f
[   77.966908][ T3661]  ieee80211_ibss_work.cold+0x30e/0x60f
[   77.972483][ T3661]  ieee80211_iface_work+0xb70/0xd00
[   77.977715][ T3661]  process_one_work+0x9ac/0x1680
[   77.982671][ T3661]  worker_thread+0x652/0x11c0
[   77.987371][ T3661]  kthread+0x405/0x4f0
[   77.991465][ T3661]  ret_from_fork+0x1f/0x30
[   77.995895][ T3661] freed in:
[   77.999006][ T3661]  linkwatch_do_dev+0x96/0x160
[   78.004014][ T3661]  __linkwatch_run_queue+0x233/0x6a0
[   78.009496][ T3661]  linkwatch_event+0x4a/0x60
[   78.014099][ T3661]  process_one_work+0x9ac/0x1680
[   78.019034][ T3661]  worker_thread+0x652/0x11c0
[   78.023719][ T3661]  kthread+0x405/0x4f0
[   78.027810][ T3661]  ret_from_fork+0x1f/0x30
[   78.042541][ T3661] ------------[ cut here ]------------
[   78.048253][ T3661] WARNING: CPU: 0 PID: 3661 at lib/ref_tracker.c:120 ref_tracker_free.cold+0x110/0x14e
[   78.062364][ T3661] Modules linked in:
[   78.066424][ T3661] CPU: 0 PID: 3661 Comm: kworker/0:5 Not tainted 5.16.0-rc4-next-20211210-syzkaller #0
[   78.076075][ T3661] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[   78.090648][ T3661] Workqueue: events linkwatch_event
[   78.095890][ T3661] RIP: 0010:ref_tracker_free.cold+0x110/0x14e
[   78.102191][ T3661] Code: ea 03 48 c1 e0 2a 0f b6 04 02 84 c0 74 04 3c 03 7e 4c 8b 7b 18 e8 6b 54 e9 fa e8 26 4d 57 f8 4c 89 ee 48 89 ef e8 fb 33 36 00 <0f> 0b 41 bd ea ff ff ff e9 bd 60 e9 fa 4c 89 f7 e8 16 45 a2 f8 e9
[   78.127211][ T3661] RSP: 0018:ffffc90002b5fb18 EFLAGS: 00010246
[   78.133684][ T3661] RAX: 0000000000000000 RBX: ffff88807467f700 RCX: 0000000000000000
[   78.141928][ T3661] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000001
[   78.150087][ T3661] RBP: ffff888057e105b8 R08: 0000000000000001 R09: ffffffff8ffa1967
[   78.158211][ T3661] R10: 0000000000000001 R11: 0000000000000000 R12: 1ffff9200056bf65
[   78.166204][ T3661] R13: 0000000000000292 R14: ffff88807467f718 R15: 00000000c0e0008c
[   78.174321][ T3661] FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
[   78.183310][ T3661] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   78.190156][ T3661] CR2: 000000c000208800 CR3: 000000007f7b5000 CR4: 00000000003506f0
[   78.198235][ T3661] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   78.206214][ T3661] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   78.214328][ T3661] Call Trace:
[   78.217679][ T3661]  <TASK>
[   78.220621][ T3661]  ? __sanitizer_cov_trace_const_cmp4+0x1c/0x70
[   78.226981][ T3661]  ? nlmsg_notify+0xbe/0x280
[   78.231607][ T3661]  ? ref_tracker_dir_exit+0x330/0x330
[   78.237654][ T3661]  ? linkwatch_do_dev+0x96/0x160
[   78.242628][ T3661]  ? __linkwatch_run_queue+0x233/0x6a0
[   78.248170][ T3661]  ? linkwatch_event+0x4a/0x60
[   78.252946][ T3661]  ? process_one_work+0x9ac/0x1680
[   78.258136][ T3661]  ? worker_thread+0x853/0x11c0
[   78.263020][ T3661]  ? kthread+0x405/0x4f0
[   78.267905][ T3661]  ? ret_from_fork+0x1f/0x30
[   78.272670][ T3661]  ? netdev_state_change+0xa1/0x130
[   78.278019][ T3661]  ? netdev_exit+0xd0/0xd0
[   78.282466][ T3661]  ? dev_activate+0x420/0xa60
[   78.287261][ T3661]  linkwatch_do_dev+0x96/0x160
[   78.292043][ T3661]  __linkwatch_run_queue+0x233/0x6a0
[   78.297505][ T3661]  ? linkwatch_do_dev+0x160/0x160
[   78.302561][ T3661]  linkwatch_event+0x4a/0x60
[   78.307225][ T3661]  process_one_work+0x9ac/0x1680
[   78.312292][ T3661]  ? pwq_dec_nr_in_flight+0x2a0/0x2a0
[   78.317757][ T3661]  ? rwlock_bug.part.0+0x90/0x90
[   78.322726][ T3661]  ? _raw_spin_lock_irq+0x41/0x50
[   78.327844][ T3661]  worker_thread+0x853/0x11c0
[   78.332543][ T3661]  ? process_one_work+0x1680/0x1680
[   78.338500][ T3661]  kthread+0x405/0x4f0
[   78.342610][ T3661]  ? set_kthread_struct+0x130/0x130

Fixes: 63f13937 ("net: linkwatch: add net device refcount tracker")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20211214051955.3569843-1-eric.dumazet@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/link_watch.c

@@ -166,7 +166,10 @@ static void linkwatch_do_dev(struct net_device *dev)
 
 		netdev_state_change(dev);
 	}
-	dev_put_track(dev, &dev->linkwatch_dev_tracker);
+	/* Note: our callers are responsible for
+	 * calling netdev_tracker_free().
+	 */
+	dev_put(dev);
 }
 
 static void __linkwatch_run_queue(int urgent_only)
@@ -209,6 +212,10 @@ static void __linkwatch_run_queue(int urgent_only)
 			list_add_tail(&dev->link_watch_list, &lweventlist);
 			continue;
 		}
+		/* We must free netdev tracker under
+		 * the spinlock protection.
+		 */
+		netdev_tracker_free(dev, &dev->linkwatch_dev_tracker);
 		spin_unlock_irq(&lweventlist_lock);
 		linkwatch_do_dev(dev);
 		do_dev--;
@@ -232,6 +239,10 @@ void linkwatch_forget_dev(struct net_device *dev)
 	if (!list_empty(&dev->link_watch_list)) {
 		list_del_init(&dev->link_watch_list);
 		clean = 1;
+		/* We must release netdev tracker under
+		 * the spinlock protection.
+		 */
+		netdev_tracker_free(dev, &dev->linkwatch_dev_tracker);
 	}
 	spin_unlock_irqrestore(&lweventlist_lock, flags);
 	if (clean)