Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

syzbot
2025-08-12T16:31:36Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=15494c34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1428caf0580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11da19a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/18a2e4bd0c4a/disk-8f5ae30d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3b5395881b25/vmlinux-8f5ae30d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e875f4e3b7ff/Image-8f5ae30d.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/cdc3889e34d0/mount_4.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=1412a842580000)

The issue was bisected to:

commit c8992cffbe7411c6da4c4416d5eecfc6b78e0fec
Author: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date: Wed Dec 1 18:55:05 2021 +0000

Bluetooth: hci_event: Use of a function table to handle Command Complete

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14d538c4580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=16d538c4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12d538c4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Fixes: c8992cffbe74 ("Bluetooth: hci_event: Use of a function table to handle Command Complete")

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common+0xcb4/0x24ac kernel/locking/mutex.c:678
Read of size 8 at addr ffff0000c99f80a0 by task khidpd_05c25886/6940

CPU: 0 UID: 0 PID: 6940 Comm: khidpd_05c25886 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/18/2025
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
print_address_description+0xa8/0x238 mm/kasan/report.c:378
print_report+0x68/0x84 mm/kasan/report.c:482
kasan_report+0xb0/0x110 mm/kasan/report.c:595
__asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
__mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
__mutex_lock_common+0xcb4/0x24ac kernel/locking/mutex.c:678
__mutex_lock kernel/locking/mutex.c:760 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1728
hidp_session_thread+0x3d0/0x46c net/bluetooth/hidp/core.c:1304
kthread+0x5fc/0x75c kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Allocated by task 6767:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:68
kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:562
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4365 [inline]
__kmalloc_noprof+0x2fc/0x4c8 mm/slub.c:4377
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
hci_alloc_dev_priv+0x2c/0x1b84 net/bluetooth/hci_core.c:2448
hci_alloc_dev include/net/bluetooth/hci_core.h:1706 [inline]
__vhci_create_device drivers/bluetooth/hci_vhci.c:399 [inline]
vhci_create_device+0x108/0x6d4 drivers/bluetooth/hci_vhci.c:471
vhci_get_user drivers/bluetooth/hci_vhci.c:528 [inline]
vhci_write+0x314/0x3d4 drivers/bluetooth/hci_vhci.c:608
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x540/0xa3c fs/read_write.c:686
ksys_write+0x120/0x210 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:746
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 6984:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:68
kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x74/0x98 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2417 [inline]
slab_free mm/slub.c:4680 [inline]
kfree+0x17c/0x474 mm/slub.c:4879
hci_release_dev+0xf48/0x1060 net/bluetooth/hci_core.c:2776
bt_host_release+0x70/0x8c net/bluetooth/hci_sysfs.c:87
device_release+0x8c/0x1ac drivers/base/core.c:-1
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x2b0/0x438 lib/kobject.c:737
put_device+0x28/0x40 drivers/base/core.c:3797
hci_free_dev+0x24/0x34 net/bluetooth/hci_core.c:2579
vhci_release+0x84/0xd0 drivers/bluetooth/hci_vhci.c:666
__fput+0x340/0x75c fs/file_table.c:468
____fput+0x20/0x58 fs/file_table.c:496
task_work_run+0x1dc/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x524/0x1a14 kernel/exit.c:961
do_group_exit+0x194/0x22c kernel/exit.c:1102
get_signal+0x11dc/0x12f8 kernel/signal.c:3034
do_signal+0x274/0x4434 arch/arm64/kernel/signal.c:1618
do_notify_resume+0xb0/0x1f4 arch/arm64/kernel/entry-common.c:152
exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:173 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:182 [inline]
el0_svc+0xb8/0x180 arch/arm64/kernel/entry-common.c:880
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Last potentially related work creation:
kasan_save_stack+0x40/0x6c mm/kasan/common.c:47
kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:548
insert_work+0x54/0x2cc kernel/workqueue.c:2184
__queue_work+0xc88/0x1210 kernel/workqueue.c:2343
queue_work_on+0xdc/0x18c kernel/workqueue.c:2390
queue_work include/linux/workqueue.h:669 [inline]
hci_cmd_timeout+0x178/0x1c8 net/bluetooth/hci_core.c:1480
process_one_work+0x7e8/0x155c kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x958/0xed8 kernel/workqueue.c:3400
kthread+0x5fc/0x75c kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Second to last potentially related work creation:
kasan_save_stack+0x40/0x6c mm/kasan/common.c:47
kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:548
insert_work+0x54/0x2cc kernel/workqueue.c:2184
__queue_work+0xdb0/0x1210 kernel/workqueue.c:2339
delayed_work_timer_fn+0x74/0x90 kernel/workqueue.c:2485
call_timer_fn+0x1b4/0x818 kernel/time/timer.c:1747
expire_timers kernel/time/timer.c:1793 [inline]
__run_timers kernel/time/timer.c:2372 [inline]
__run_timer_base+0x54c/0x76c kernel/time/timer.c:2384
run_timer_base kernel/time/timer.c:2393 [inline]
run_timer_softirq+0xcc/0x194 kernel/time/timer.c:2403
handle_softirqs+0x328/0xc88 kernel/softirq.c:579
__do_softirq+0x14/0x20 kernel/softirq.c:613

The buggy address belongs to the object at ffff0000c99f8000
which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 160 bytes inside of
freed 8192-byte region [ffff0000c99f8000, ffff0000c99fa000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1099f8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x5ffc00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000040 ffff0000c0002280 fffffdffc374ca00 0000000000000005
raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c0002280 fffffdffc374ca00 0000000000000005
head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc3267e01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000c99f7f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff0000c99f8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000c99f8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000c99f8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000c99f8180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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