From 8eed5519e496b7a07f441a0f579cb228a33189f7 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 11 Jun 2026 15:27:37 +0000 Subject: net: watchdog: fix refcount tracking races Blamed commit converted the untracked dev_hold()/dev_put() calls in the watchdog code to use the tracked dev_hold_track()/dev_put_track() (which were later renamed/interfaced to netdev_hold() and netdev_put()). By introducing dev->watchdog_dev_tracker to store the reference tracking information without adding synchronization between netdev_watchdog_up() and dev_watchdog(), it enabled the race condition where this pointer could be overwritten or freed concurrently, leading to the list corruption crash syzbot reported: list_del corruption, ffff888114a18c00->next is NULL kernel BUG at lib/list_debug.c:52 ! Oops: invalid opcode: 0000 [#1] SMP KASAN PTI CPU: 1 UID: 0 PID: 91 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(lazy) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Workqueue: events_unbound linkwatch_event RIP: 0010:__list_del_entry_valid_or_report.cold+0x22/0x2a lib/list_debug.c:52 Call Trace: __list_del_entry_valid include/linux/list.h:132 [inline] __list_del_entry include/linux/list.h:246 [inline] list_move_tail include/linux/list.h:341 [inline] ref_tracker_free+0x1a7/0x6c0 lib/ref_tracker.c:329 netdev_tracker_free include/linux/netdevice.h:4491 [inline] netdev_put include/linux/netdevice.h:4508 [inline] netdev_put include/linux/netdevice.h:4504 [inline] netdev_watchdog_down net/sched/sch_generic.c:600 [inline] dev_deactivate_many+0x28c/0xfe0 net/sched/sch_generic.c:1363 dev_deactivate+0x109/0x1d0 net/sched/sch_generic.c:1397 linkwatch_do_dev net/core/link_watch.c:184 [inline] linkwatch_do_dev+0xd3/0x120 net/core/link_watch.c:166 __linkwatch_run_queue+0x3a5/0x810 net/core/link_watch.c:240 linkwatch_event+0x8f/0xc0 net/core/link_watch.c:314 process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314 process_scheduled_works kernel/workqueue.c:3397 [inline] worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478 kthread+0x370/0x450 kernel/kthread.c:436 ret_from_fork+0x69a/0xc80 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 This patch has three coordinated parts: 1) Add dev->watchdog_lock and dev->watchdog_ref_held to serialize watchdog operations. 2) Remove netdev_watchdog_up() call from netif_carrier_on(): This ensures netdev_watchdog_up() is only called from process/BH context (via linkwatch workqueue dev_activate()), allowing us to use spin_lock_bh() for synchronization. 3) Synchronize watchdog up and watchdog timer: Protect netdev_watchdog_up() with tx_global_lock and watchdog_lock. Only allocate a new tracker in netdev_watchdog_up() if one is not already present. In dev_watchdog(), ensure we don't release the tracker if the timer was rescheduled either by dev_watchdog() itself or concurrently by netdev_watchdog_up(). Fixes: f12bf6f3f942 ("net: watchdog: add net device refcount tracker") Reported-by: syzbot+381d82bbf0253710b35d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a26b751.c25708ab.1b19ef.0013.GAE@google.com/T/#u Tested-by: syzbot+3479efbc2821cb2a79f2@syzkaller.appspotmail.com Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260611152737.2580480-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- include/linux/netdevice.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux/netdevice.h') diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 0e1e581efc5a..4a0e83709f29 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -1980,6 +1980,8 @@ enum netdev_reg_state { * @qdisc_hash: qdisc hash table * @watchdog_timeo: Represents the timeout that is used by * the watchdog (see dev_watchdog()) + * @watchdog_lock: protect watchdog_ref_held + * @watchdog_ref_held: True if the watchdog device ref is taken. * @watchdog_timer: List of timers * * @proto_down_reason: reason a netdev interface is held down @@ -2392,6 +2394,8 @@ struct net_device { /* These may be needed for future network-power-down code. */ struct timer_list watchdog_timer; int watchdog_timeo; + spinlock_t watchdog_lock; + bool watchdog_ref_held; u32 proto_down_reason; -- cgit v1.2.3