Subject: Re: [PATCH v2 net] tipc: Fix use-after-free in tipc_mon_reinit_self().

From: Simon Horman <[email-masked]>
Date: Mon, 10 Nov 2025 19:11:56 +0000

On Fri, Nov 07, 2025 at 06:40:25AM +0000, Kuniyuki Iwashima wrote:
> syzbot reported use-after-free of tipc_net(net)->monitors[]
> in tipc_mon_reinit_self(). [0]
> 
> The array is protected by RTNL, but tipc_mon_reinit_self()
> iterates over it without RTNL.
> 
> tipc_mon_reinit_self() is called from tipc_net_finalize(),
> which is always under RTNL except for tipc_net_finalize_work().
> 
> Let's hold RTNL in tipc_net_finalize_work().
> 
> [0]:
> BUG: KASAN: slab-use-after-free in __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0xa7/0xf0 kernel/locking/spinlock.c:162
> Read of size 1 at addr ffff88805eae1030 by task kworker/0:7/5989
> 
> CPU: 0 UID: 0 PID: 5989 Comm: kworker/0:7 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> Workqueue: events tipc_net_finalize_work
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:378 [inline]
>  print_report+0xca/0x240 mm/kasan/report.c:482
>  kasan_report+0x118/0x150 mm/kasan/report.c:595
>  __kasan_check_byte+0x2a/0x40 mm/kasan/common.c:568
>  kasan_check_byte include/linux/kasan.h:399 [inline]
>  lock_acquire+0x8d/0x360 kernel/locking/lockdep.c:5842
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0xa7/0xf0 kernel/locking/spinlock.c:162
>  rtlock_slowlock kernel/locking/rtmutex.c:1894 [inline]
>  rwbase_rtmutex_lock_state kernel/locking/spinlock_rt.c:160 [inline]
>  rwbase_write_lock+0xd3/0x7e0 kernel/locking/rwbase_rt.c:244
>  rt_write_lock+0x76/0x110 kernel/locking/spinlock_rt.c:243
>  write_lock_bh include/linux/rwlock_rt.h:99 [inline]
>  tipc_mon_reinit_self+0x79/0x430 net/tipc/monitor.c:718
>  tipc_net_finalize+0x115/0x190 net/tipc/net.c:140
>  process_one_work kernel/workqueue.c:3236 [inline]
>  process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3319
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>  ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> 
> Allocated by task 6089:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
>  kasan_kmalloc include/linux/kasan.h:260 [inline]
>  __kmalloc_cache_noprof+0x1a8/0x320 mm/slub.c:4407
>  kmalloc_noprof include/linux/slab.h:905 [inline]
>  kzalloc_noprof include/linux/slab.h:1039 [inline]
>  tipc_mon_create+0xc3/0x4d0 net/tipc/monitor.c:657
>  tipc_enable_bearer net/tipc/bearer.c:357 [inline]
>  __tipc_nl_bearer_enable+0xe16/0x13f0 net/tipc/bearer.c:1047
>  __tipc_nl_compat_doit net/tipc/netlink_compat.c:371 [inline]
>  tipc_nl_compat_doit+0x3bc/0x5f0 net/tipc/netlink_compat.c:393
>  tipc_nl_compat_handle net/tipc/netlink_compat.c:-1 [inline]
>  tipc_nl_compat_recv+0x83c/0xbe0 net/tipc/netlink_compat.c:1321
>  genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
>  genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>  genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
>  netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>  netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
>  netlink_unicast+0x846/0xa10 net/netlink/af_netlink.c:1346
>  netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
>  sock_sendmsg_nosec net/socket.c:714 [inline]
>  __sock_sendmsg+0x21c/0x270 net/socket.c:729
>  ____sys_sendmsg+0x508/0x820 net/socket.c:2614
>  ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
>  __sys_sendmsg net/socket.c:2700 [inline]
>  __do_sys_sendmsg net/socket.c:2705 [inline]
>  __se_sys_sendmsg net/socket.c:2703 [inline]
>  __x64_sys_sendmsg+0x1a1/0x260 net/socket.c:2703
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 6088:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
>  poison_slab_object mm/kasan/common.c:243 [inline]
>  __kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275
>  kasan_slab_free include/linux/kasan.h:233 [inline]
>  slab_free_hook mm/slub.c:2422 [inline]
>  slab_free mm/slub.c:4695 [inline]
>  kfree+0x195/0x550 mm/slub.c:4894
>  tipc_l2_device_event+0x380/0x650 net/tipc/bearer.c:-1
>  notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
>  call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
>  call_netdevice_notifiers net/core/dev.c:2281 [inline]
>  unregister_netdevice_many_notify+0x14d7/0x1fe0 net/core/dev.c:12166
>  unregister_netdevice_many net/core/dev.c:12229 [inline]
>  unregister_netdevice_queue+0x33c/0x380 net/core/dev.c:12073
>  unregister_netdevice include/linux/netdevice.h:3385 [inline]
>  __tun_detach+0xe4d/0x1620 drivers/net/tun.c:621
>  tun_detach drivers/net/tun.c:637 [inline]
>  tun_chr_close+0x10d/0x1c0 drivers/net/tun.c:3433
>  __fput+0x458/0xa80 fs/file_table.c:468
>  task_work_run+0x1d4/0x260 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop+0xec/0x110 kernel/entry/common.c:43
>  exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
>  syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
>  do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: 46cb01eeeb86 ("tipc: update mon's self addr when node addr generated")
> Reported-by: [email-masked]
> Closes: https://lore.kernel.org/netdev/[email-masked]/
> Signed-off-by: Kuniyuki Iwashima <[email-masked]>
> ---
> v2: Wrap tipc_net_finalize_work() with RTNL (Jakub)
> v1: https://lore.kernel.org/netdev/[email-masked]/

Thanks Iwashima-san,

I agree with the analysis above.

Reviewed-by: Simon Horman <[email-masked]>