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Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Kuniyuki Iwashima , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet , syzbot+381d82bbf0253710b35d@syzkaller.appspotmail.com, syzbot+3479efbc2821cb2a79f2@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" 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) Zero tracker on free: Modify netdev_tracker_free() to poison the tracker pointer after freeing. This helps detect and avoid double frees. 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. Only allocate a new tracker in netdev_watchdog_up() if one is not already present. In dev_watchdog(), keep the lock held while calling netdev_put() to avoid races with concurrent netdev_watchdog_up(). 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 --- include/linux/netdevice.h | 7 ++++++- net/sched/sch_generic.c | 26 +++++++++++++++----------- 2 files changed, 21 insertions(+), 12 deletions(-) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 0e1e581efc5ac264259b2f0fdfe41c50a6f47239..fb9f7cee1d29de5367ea902d352296f952525c57 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -4488,7 +4488,12 @@ static inline void netdev_tracker_free(struct net_device *dev, netdevice_tracker *tracker) { #ifdef CONFIG_NET_DEV_REFCNT_TRACKER - ref_tracker_free(&dev->refcnt_tracker, tracker); + if (!tracker) { + ref_tracker_free(&dev->refcnt_tracker, NULL); + } else if (!IS_ERR(*tracker)) { + ref_tracker_free(&dev->refcnt_tracker, tracker); + *tracker = ERR_PTR(-EEXIST); + } #endif } diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index a93321db8fd75d30c61e146c290bbc139c37c913..6ca7cec17b3164a481e72368376315d9b9d289cd 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -568,16 +568,18 @@ static void dev_watchdog(struct timer_list *t) dev->netdev_ops->ndo_tx_timeout(dev, i); netif_unfreeze_queues(dev); } - if (!mod_timer(&dev->watchdog_timer, - round_jiffies(oldest_start + - dev->watchdog_timeo))) - release = false; + mod_timer(&dev->watchdog_timer, + round_jiffies(oldest_start + + dev->watchdog_timeo)); + release = false; } } - spin_unlock(&dev->tx_global_lock); - + if (timer_pending(&dev->watchdog_timer)) + release = false; if (release) netdev_put(dev, &dev->watchdog_dev_tracker); + + spin_unlock(&dev->tx_global_lock); } void netdev_watchdog_up(struct net_device *dev) @@ -586,10 +588,14 @@ void netdev_watchdog_up(struct net_device *dev) return; if (dev->watchdog_timeo <= 0) dev->watchdog_timeo = 5*HZ; + spin_lock_bh(&dev->tx_global_lock); if (!mod_timer(&dev->watchdog_timer, - round_jiffies(jiffies + dev->watchdog_timeo))) - netdev_hold(dev, &dev->watchdog_dev_tracker, - GFP_ATOMIC); + round_jiffies(jiffies + dev->watchdog_timeo))) { + if (IS_ERR_OR_NULL(dev->watchdog_dev_tracker)) + netdev_hold(dev, &dev->watchdog_dev_tracker, + GFP_ATOMIC); + } + spin_unlock_bh(&dev->tx_global_lock); } EXPORT_SYMBOL_GPL(netdev_watchdog_up); @@ -614,8 +620,6 @@ void netif_carrier_on(struct net_device *dev) return; atomic_inc(&dev->carrier_up_count); linkwatch_fire_event(dev); - if (netif_running(dev)) - netdev_watchdog_up(dev); } } EXPORT_SYMBOL(netif_carrier_on); -- 2.54.0.1032.g2f8565e1d1-goog