[PATCH v1 net] nfc: nci: Fix race between rfkill and nci_unregister_device().

[PATCH v1 net] nfc: nci: Fix race between rfkill and nci_unregister_device().

[Kuniyuki Iwashima]

syzbot reported the splat below [0] without a repro.

It indicates that struct nci_dev.cmd_wq had been destroyed before
nci_close_device() was called via rfkill.

nci_dev.cmd_wq is only destroyed in nci_unregister_device(), which
(I think) was called from virtual_ncidev_close() when syzbot close()d
an fd of virtual_ncidev.

The problem is that nci_unregister_device() destroys nci_dev.cmd_wq
first and then calls nfc_unregister_device(), which removes the
device from rfkill by rfkill_unregister().

So, the device is still visible via rfkill even after nci_dev.cmd_wq
is destroyed.

Let's call nfc_unregister_device() first in nci_unregister_device().

[0]:
DEBUG_LOCKS_WARN_ON(1)
WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:238 [inline], CPU#0: syz.0.8675/6349
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4854 [inline], CPU#0: syz.0.8675/6349
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x39d/0x2cf0 kernel/locking/lockdep.c:5187, CPU#0: syz.0.8675/6349
Modules linked in:
CPU: 0 UID: 0 PID: 6349 Comm: syz.0.8675 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4854 [inline]
RIP: 0010:__lock_acquire+0x3a4/0x2cf0 kernel/locking/lockdep.c:5187
Code: 18 00 4c 8b 74 24 08 75 27 90 e8 17 f2 fc 02 85 c0 74 1c 83 3d 50 e0 4e 0e 00 75 13 48 8d 3d 43 f7 51 0e 48 c7 c6 8b 3a de 8d <67> 48 0f b9 3a 90 31 c0 0f b6 98 c4 00 00 00 41 8b 45 20 25 ff 1f
RSP: 0018:ffffc9000c767680 EFLAGS: 00010046
RAX: 0000000000000001 RBX: 0000000000040000 RCX: 0000000000080000
RDX: ffffc90013080000 RSI: ffffffff8dde3a8b RDI: ffffffff8ff24ca0
RBP: 0000000000000003 R08: ffffffff8fef35a3 R09: 1ffffffff1fde6b4
R10: dffffc0000000000 R11: fffffbfff1fde6b5 R12: 00000000000012a2
R13: ffff888030338ba8 R14: ffff888030338000 R15: ffff888030338b30
FS:  00007fa5995f66c0(0000) GS:ffff8881256f8000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7e72f842d0 CR3: 00000000485a0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
 touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:3940
 __flush_workqueue+0x14b/0x14f0 kernel/workqueue.c:3982
 nci_close_device+0x302/0x630 net/nfc/nci/core.c:567
 nci_dev_down+0x3b/0x50 net/nfc/nci/core.c:639
 nfc_dev_down+0x152/0x290 net/nfc/core.c:161
 nfc_rfkill_set_block+0x2d/0x100 net/nfc/core.c:179
 rfkill_set_block+0x1d2/0x440 net/rfkill/core.c:346
 rfkill_fop_write+0x461/0x5a0 net/rfkill/core.c:1301
 vfs_write+0x29a/0xb90 fs/read_write.c:684
 ksys_write+0x150/0x270 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa59b39acb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa5995f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fa59b615fa0 RCX: 00007fa59b39acb9
RDX: 0000000000000008 RSI: 0000200000000080 RDI: 0000000000000007
RBP: 00007fa59b408bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa59b616038 R14: 00007fa59b615fa0 R15: 00007ffc82218788
 </TASK>

Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
Reported-by: syzbot+f9c5fd1a0874f9069dce@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/695e7f56.050a0220.1c677c.036c.GAE@google.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/nfc/nci/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index fc921cd2cdff..df8a2f97026f 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -1303,6 +1303,8 @@ void nci_unregister_device(struct nci_dev *ndev)
 {
 	struct nci_conn_info *conn_info, *n;
 
+	nfc_unregister_device(ndev->nfc_dev);
+
 	/* This set_bit is not protected with specialized barrier,
 	 * However, it is fine because the mutex_lock(&ndev->req_lock);
 	 * in nci_close_device() will help to emit one.
@@ -1319,8 +1321,6 @@ void nci_unregister_device(struct nci_dev *ndev)
 		list_del(&conn_info->list);
 		/* conn_info is allocated with devm_kzalloc */
 	}
-
-	nfc_unregister_device(ndev->nfc_dev);
 }
 EXPORT_SYMBOL(nci_unregister_device);
 
-- 
2.52.0.457.g6b5491de43-goog

[syzbot ci] Re: nfc: nci: Fix race between rfkill and nci_unregister_device().

[syzbot ci]

syzbot ci has tested the following series

[v1] nfc: nci: Fix race between rfkill and nci_unregister_device().
https://lore.kernel.org/all/20260126071359.2693214-1-kuniyu@google.com
* [PATCH v1 net] nfc: nci: Fix race between rfkill and nci_unregister_device().

and found the following issue:
KASAN: slab-use-after-free Read in nci_unregister_device

Full report is available here:
https://ci.syzbot.org/series/1b1f8783-f1b1-4eaf-8140-aeb610bb4b90

***

KASAN: slab-use-after-free Read in nci_unregister_device

tree:      net
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base:      1742272bd3fae6362301d0f11eb9db9030348afc
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/f8117535-23ea-4dd0-8208-c2a71b5d6f69/config
C repro:   https://ci.syzbot.org/findings/0d078d52-d526-410a-b2a3-55b7b314bf59/c_repro
syz repro: https://ci.syzbot.org/findings/0d078d52-d526-410a-b2a3-55b7b314bf59/syz_repro

==================================================================
BUG: KASAN: slab-use-after-free in nci_unregister_device+0x123/0x230 net/nfc/nci/core.c:1320
Read of size 8 at addr ffff888113d56628 by task syz.0.17/5980

CPU: 1 UID: 0 PID: 5980 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 nci_unregister_device+0x123/0x230 net/nfc/nci/core.c:1320
 virtual_ncidev_close+0x56/0x90 drivers/nfc/virtual_ncidev.c:168
 __fput+0x44f/0xa70 fs/file_table.c:468
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2b7/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f148199acb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff4e2266c8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f1481c17da0 RCX: 00007f148199acb9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f1481c17da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007f1481c17cb0 R11: 0000000000000246 R12: 0000000000012770
R13: 00007f1481c1609c R14: 00000000000124bb R15: 00007f1481c16090
 </TASK>

Allocated by task 13:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5657 [inline]
 __kmalloc_node_track_caller_noprof+0x558/0x7f0 mm/slub.c:5768
 alloc_dr drivers/base/devres.c:119 [inline]
 devm_kmalloc+0x7f/0x300 drivers/base/devres.c:864
 devm_kzalloc include/linux/device/devres.h:54 [inline]
 nci_core_conn_create_rsp_packet net/nfc/nci/rsp.c:282 [inline]
 nci_rsp_packet+0x894/0x3200 net/nfc/nci/rsp.c:384
 nci_rx_work+0x1f8/0x3f0 net/nfc/nci/core.c:1551
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xaec/0x17a0 kernel/workqueue.c:3340
 worker_thread+0x89f/0xd90 kernel/workqueue.c:3421
 kthread+0x726/0x8b0 kernel/kthread.c:463
 ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Freed by task 5980:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6674 [inline]
 kfree+0x1be/0x650 mm/slub.c:6882
 release_nodes drivers/base/devres.c:506 [inline]
 devres_release_all+0x1b2/0x240 drivers/base/devres.c:535
 device_del+0x736/0x8f0 drivers/base/core.c:3893
 nfc_unregister_device+0x19c/0x330 net/nfc/core.c:1188
 nci_unregister_device+0x42/0x230 net/nfc/nci/core.c:1306
 virtual_ncidev_close+0x56/0x90 drivers/nfc/virtual_ncidev.c:168
 __fput+0x44f/0xa70 fs/file_table.c:468
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2b7/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888113d56600
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 40 bytes inside of
 freed 128-byte region [ffff888113d56600, ffff888113d56680)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888113d56900 pfn:0x113d56
flags: 0x17ff00000000200(workingset|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000200 ffff888100041a00 ffff888100040648 ffffea00044fbf90
raw: ffff888113d56900 000000000010000c 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5277, tgid 5277 (udevadm), ts 29935854573, free_ts 29929951093
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
 prep_new_page mm/page_alloc.c:1892 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3945
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5240
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
 alloc_slab_page mm/slub.c:3075 [inline]
 allocate_slab+0x86/0x3a0 mm/slub.c:3248
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xd82/0x1760 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __kmalloc_cache_noprof+0x40d/0x6e0 mm/slub.c:5775
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 kernfs_get_open_node fs/kernfs/file.c:543 [inline]
 kernfs_fop_open+0x7b5/0xca0 fs/kernfs/file.c:718
 do_dentry_open+0x7ce/0x1420 fs/open.c:962
 vfs_open+0x3b/0x340 fs/open.c:1094
 do_open fs/namei.c:4637 [inline]
 path_openat+0x3486/0x3e20 fs/namei.c:4796
 do_filp_open+0x22d/0x490 fs/namei.c:4823
 do_sys_openat2+0x12f/0x220 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_openat fs/open.c:1452 [inline]
 __se_sys_openat fs/open.c:1447 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1447
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
page last free pid 5277 tgid 5277 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xbb0/0xd10 mm/page_alloc.c:2973
 __slab_free+0x2ce/0x320 mm/slub.c:6008
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_noprof+0x3c2/0x7e0 mm/slub.c:5669
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kernfs_fop_write_iter+0x158/0x540 fs/kernfs/file.c:329
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x61d/0xb90 fs/read_write.c:686
 ksys_write+0x150/0x270 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888113d56500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888113d56580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888113d56600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff888113d56680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888113d56700: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
==================================================================


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.