syzbot


WARNING: locking bug in l2cap_unregister_user

Status: upstream: reported on 2025/12/25 03:40
Subsystems: bluetooth
[Documentation on labels]
Reported-by: syzbot+a97711deac466a4afeac@syzkaller.appspotmail.com
First crash: 53d, last: 12d
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [bluetooth?] WARNING: locking bug in l2cap_unregister_user 0 (1) 2025/12/25 03:40

Sample crash report:
------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(1)
WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:-1 [inline], CPU#1: khidpd_15c30006/6734
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4854 [inline], CPU#1: khidpd_15c30006/6734
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187, CPU#1: khidpd_15c30006/6734
Modules linked in:
CPU: 1 UID: 0 PID: 6734 Comm: khidpd_15c30006 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : hlock_class kernel/locking/lockdep.c:-1 [inline]
pc : check_wait_context kernel/locking/lockdep.c:4854 [inline]
pc : __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187
lr : hlock_class kernel/locking/lockdep.c:238 [inline]
lr : check_wait_context kernel/locking/lockdep.c:4854 [inline]
lr : __lock_acquire+0x378/0x30a4 kernel/locking/lockdep.c:5187
sp : ffff8000a00c7820
x29: ffff8000a00c7900 x28: 0000000000000001 x27: ffff0000cc2de078
x26: ffff80008afabde8 x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000000 x22: 0000000000000000 x21: ffff0000cc2dd580
x20: ffff8000975d1000 x19: 0000000000000000 x18: 1fffe00033781890
x17: ffff80008f86e000 x16: ffff800082e5e68c x15: 0000000000000001
x14: 1fffe000337818fa x13: 0000000000000000 x12: 0000000000000000
x11: ffff800093398d48 x10: 0000000000ff0100 x9 : 1cca0337e3f42500
x8 : 0000000000000000 x7 : 4e5241575f534b43 x6 : ffff8000805761f8
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000807f1034
x2 : 0000000000000001 x1 : 0000000100000002 x0 : 0000000000000000
Call trace:
 hlock_class kernel/locking/lockdep.c:-1 [inline] (P)
 check_wait_context kernel/locking/lockdep.c:4854 [inline] (P)
 __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187 (P)
 lock_acquire+0x140/0x2e0 kernel/locking/lockdep.c:5868
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
 class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
 set_task_blocked_on include/linux/sched.h:2165 [inline]
 __mutex_lock_common+0xd24/0x2678 kernel/locking/mutex.c:701
 __mutex_lock kernel/locking/mutex.c:776 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:828
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1729
 hidp_session_thread+0x3d0/0x490 net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844
irq event stamp: 72
hardirqs last  enabled at (71): [<ffff80008049eb1c>] raw_spin_rq_unlock_irq kernel/sched/sched.h:1570 [inline]
hardirqs last  enabled at (71): [<ffff80008049eb1c>] finish_lock_switch+0xb0/0x1c0 kernel/sched/core.c:4995
hardirqs last disabled at (72): [<ffff80008afbc254>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (72): [<ffff80008afbc254>] _raw_spin_lock_irqsave+0x2c/0x7c kernel/locking/spinlock.c:162
softirqs last  enabled at (0): [<ffff8000803bf65c>] copy_process+0x10a8/0x32fc kernel/fork.c:2167
softirqs last disabled at (0): [<0000000000000000>] 0x0
---[ end trace 0000000000000000 ]---
Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c4
Mem abort info:
  ESR = 0x0000000096000005
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x05: level 1 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=000000010f7e0000
[00000000000000c4] pgd=080000013c244403, p4d=080000013c244403, pud=0000000000000000
Internal error: Oops: 0000000096000005 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 6734 Comm: khidpd_15c30006 Tainted: G        W           syzkaller #0 PREEMPT 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : check_wait_context kernel/locking/lockdep.c:4854 [inline]
pc : __lock_acquire+0x398/0x30a4 kernel/locking/lockdep.c:5187
lr : hlock_class kernel/locking/lockdep.c:238 [inline]
lr : check_wait_context kernel/locking/lockdep.c:4854 [inline]
lr : __lock_acquire+0x378/0x30a4 kernel/locking/lockdep.c:5187
sp : ffff8000a00c7820
x29: ffff8000a00c7900 x28: 0000000000000001 x27: ffff0000cc2de078
x26: ffff80008afabde8 x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000000 x22: 0000000000000000 x21: ffff0000cc2dd580
x20: ffff8000975d1000 x19: 0000000000000000 x18: 1fffe00033781890
x17: ffff80008f86e000 x16: ffff800082e5e68c x15: 0000000000000001
x14: 1fffe000337818fa x13: 0000000000000000 x12: 0000000000000000
x11: ffff800093398d48 x10: 0000000000ff0100 x9 : 00000000000c0c6f
x8 : 0000000000000000 x7 : 4e5241575f534b43 x6 : ffff8000805761f8
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000807f1034
x2 : 0000000000000001 x1 : 0000000100000002 x0 : 0000000000000000
Call trace:
 hlock_class kernel/locking/lockdep.c:229 [inline] (P)
 check_wait_context kernel/locking/lockdep.c:4855 [inline] (P)
 __lock_acquire+0x398/0x30a4 kernel/locking/lockdep.c:5187 (P)
 lock_acquire+0x140/0x2e0 kernel/locking/lockdep.c:5868
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
 class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
 set_task_blocked_on include/linux/sched.h:2165 [inline]
 __mutex_lock_common+0xd24/0x2678 kernel/locking/mutex.c:701
 __mutex_lock kernel/locking/mutex.c:776 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:828
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1729
 hidp_session_thread+0x3d0/0x490 net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844
Code: 14000003 d00972eb 9135216b b9402369 (39431113) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	14000003 	b	0xc
   4:	d00972eb 	adrp	x11, 0x12e5e000
   8:	9135216b 	add	x11, x11, #0xd48
   c:	b9402369 	ldr	w9, [x27, #32]
* 10:	39431113 	ldrb	w19, [x8, #196] <-- trapping instruction

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/30 09:52 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 59e4d31a0470 bfa73b7b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
2026/01/21 08:03 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 59e4d31a0470 2494e18d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
2026/01/19 08:39 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 59e4d31a0470 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
2026/01/04 19:24 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 8f0b4cce4481 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
2025/12/27 18:54 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 8f0b4cce4481 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
2025/12/21 03:32 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 8f0b4cce4481 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: locking bug in l2cap_unregister_user
* Struck through repros no longer work on HEAD.