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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 90602c251cda Merge tag 'net-6.12-rc6' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10076630580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4340261e4e9f37fc
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15bd9340580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-90602c25.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a2daa3dcb25/vmlinux-90602c25.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4488ee6eec29/bzImage-90602c25.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14b6d5...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:686 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
Read of size 8 at addr ffff888021760060 by task khidpd_0007fff9/6116

CPU: 3 UID: 0 PID: 6116 Comm: khidpd_0007fff9 Not tainted 6.12.0-rc5-syzkaller-00161-g90602c251cda #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:377 [inline]
print_report+0xc3/0x620 mm/kasan/report.c:488
kasan_report+0xd9/0x110 mm/kasan/report.c:601
__mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
__mutex_lock_common kernel/locking/mutex.c:686 [inline]
__mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
l2cap_unregister_user+0x71/0x240 net/bluetooth/l2cap_core.c:1726
hidp_session_thread+0x462/0x650 net/bluetooth/hidp/core.c:1304
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>

Allocated by task 6062:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
kasan_kmalloc include/linux/kasan.h:257 [inline]
__do_kmalloc_node mm/slub.c:4264 [inline]
__kmalloc_noprof+0x1e8/0x400 mm/slub.c:4276
kmalloc_noprof include/linux/slab.h:882 [inline]
kzalloc_noprof include/linux/slab.h:1014 [inline]
hci_alloc_dev_priv+0x1d/0x2820 net/bluetooth/hci_core.c:2440
hci_alloc_dev include/net/bluetooth/hci_core.h:1621 [inline]
__vhci_create_device+0xef/0x7d0 drivers/bluetooth/hci_vhci.c:399
vhci_create_device drivers/bluetooth/hci_vhci.c:470 [inline]
vhci_get_user drivers/bluetooth/hci_vhci.c:527 [inline]
vhci_write+0x2c3/0x470 drivers/bluetooth/hci_vhci.c:607
new_sync_write fs/read_write.c:590 [inline]
vfs_write+0x5ae/0x1150 fs/read_write.c:683
ksys_write+0x12f/0x260 fs/read_write.c:736
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6062:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:579
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:2342 [inline]
slab_free mm/slub.c:4579 [inline]
kfree+0x14f/0x4b0 mm/slub.c:4727
hci_release_dev+0x4d9/0x600 net/bluetooth/hci_core.c:2759
bt_host_release+0x6a/0xb0 net/bluetooth/hci_sysfs.c:94
device_release+0xa1/0x240 drivers/base/core.c:2575
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x1e4/0x5a0 lib/kobject.c:737
put_device+0x1f/0x30 drivers/base/core.c:3783
vhci_release+0x81/0xf0 drivers/bluetooth/hci_vhci.c:665
__fput+0x3f6/0xb60 fs/file_table.c:431
task_work_run+0x14e/0x250 kernel/task_work.c:239
exit_task_work include/linux/task_work.h:43 [inline]
do_exit+0xadd/0x2d70 kernel/exit.c:939
do_group_exit+0xd3/0x2a0 kernel/exit.c:1088
__do_sys_exit_group kernel/exit.c:1099 [inline]
__se_sys_exit_group kernel/exit.c:1097 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1097
x64_sys_call+0x14a9/0x16a0 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Last potentially related work creation:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
__kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
insert_work+0x36/0x230 kernel/workqueue.c:2183
__queue_work+0x3f8/0x1080 kernel/workqueue.c:2343
queue_work_on+0x11a/0x140 kernel/workqueue.c:2390
process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3229
process_scheduled_works kernel/workqueue.c:3310 [inline]
worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Second to last potentially related work creation:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
__kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
insert_work+0x36/0x230 kernel/workqueue.c:2183
__queue_work+0x97e/0x1080 kernel/workqueue.c:2339
call_timer_fn+0x1a0/0x610 kernel/time/timer.c:1794
expire_timers kernel/time/timer.c:1840 [inline]
__run_timers+0x56a/0x930 kernel/time/timer.c:2419
__run_timer_base kernel/time/timer.c:2430 [inline]
__run_timer_base kernel/time/timer.c:2423 [inline]
run_timer_base+0x111/0x190 kernel/time/timer.c:2439
run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2449
handle_softirqs+0x213/0x8f0 kernel/softirq.c:554
__do_softirq kernel/softirq.c:588 [inline]
invoke_softirq kernel/softirq.c:428 [inline]
__irq_exit_rcu kernel/softirq.c:637 [inline]
irq_exit_rcu+0xbb/0x120 kernel/softirq.c:649
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1049
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

The buggy address belongs to the object at ffff888021760000
which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 96 bytes inside of
freed 8192-byte region [ffff888021760000, ffff888021762000)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x21760
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b043180 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000040 ffff88801b043180 dead000000000100 dead000000000122
head: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000003 ffffea000085d801 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5654, tgid 5654 (sh), ts 21301582122, free_ts 21285906849
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1537
prep_new_page mm/page_alloc.c:1545 [inline]
get_page_from_freelist+0x101e/0x3070 mm/page_alloc.c:3457
__alloc_pages_noprof+0x223/0x25a0 mm/page_alloc.c:4733
alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2265
alloc_slab_page mm/slub.c:2412 [inline]
allocate_slab mm/slub.c:2578 [inline]
new_slab+0x2ba/0x3f0 mm/slub.c:2631
___slab_alloc+0xdac/0x1880 mm/slub.c:3818
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3908
__slab_alloc_node mm/slub.c:3961 [inline]
slab_alloc_node mm/slub.c:4122 [inline]
__kmalloc_cache_noprof+0x2b4/0x300 mm/slub.c:4290
kmalloc_noprof include/linux/slab.h:878 [inline]
kzalloc_noprof include/linux/slab.h:1014 [inline]
tomoyo_print_bprm security/tomoyo/audit.c:26 [inline]
tomoyo_init_log+0xcb3/0x2170 security/tomoyo/audit.c:264
tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
tomoyo_execute_permission+0x38e/0x4b0 security/tomoyo/file.c:619
tomoyo_find_next_domain+0x361/0x2070 security/tomoyo/domain.c:755
tomoyo_bprm_check_security security/tomoyo/tomoyo.c:102 [inline]
tomoyo_bprm_check_security+0x12b/0x1d0 security/tomoyo/tomoyo.c:92
security_bprm_check+0x1b9/0x1e0 security/security.c:1297
search_binary_handler fs/exec.c:1740 [inline]
exec_binprm fs/exec.c:1794 [inline]
bprm_execve fs/exec.c:1845 [inline]
bprm_execve+0x642/0x1960 fs/exec.c:1821
do_execveat_common.isra.0+0x4f1/0x630 fs/exec.c:1952
page last free pid 5653 tgid 5653 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1108 [inline]
free_unref_page+0x5f4/0xdc0 mm/page_alloc.c:2638
__put_partials+0x14c/0x170 mm/slub.c:3145
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x4e/0x120 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x192/0x1e0 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
kasan_slab_alloc include/linux/kasan.h:247 [inline]
slab_post_alloc_hook mm/slub.c:4085 [inline]
slab_alloc_node mm/slub.c:4134 [inline]
__kmalloc_cache_noprof+0x11e/0x300 mm/slub.c:4290
kmalloc_noprof include/linux/slab.h:878 [inline]
tomoyo_print_header security/tomoyo/audit.c:156 [inline]
tomoyo_init_log+0x195/0x2170 security/tomoyo/audit.c:255
tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
tomoyo_path_permission security/tomoyo/file.c:587 [inline]
tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:573
tomoyo_path_perm+0x35e/0x450 security/tomoyo/file.c:838
security_inode_getattr+0x116/0x290 security/security.c:2373
vfs_getattr+0x36/0xb0 fs/stat.c:204
vfs_statx_path+0x36/0x390 fs/stat.c:251
vfs_statx+0x145/0x1e0 fs/stat.c:315
vfs_fstatat+0x9f/0x160 fs/stat.c:341
__do_sys_newfstatat+0xa2/0x130 fs/stat.c:505

Memory state around the buggy address:
ffff88802175ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802175ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888021760000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888021760080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888021760100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Hillf Danton]

On Fri, 01 Nov 2024 11:29:21 -0700

> syzbot found the following issue on:
>
> HEAD commit: 90602c251cda Merge tag 'net-6.12-rc6' of git://git.kernel...
> git tree: upstream

> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15bd9340580000

#syz test

--- l/net/bluetooth/hidp/core.c
+++ y/net/bluetooth/hidp/core.c
@@ -1302,6 +1302,7 @@ static int hidp_session_thread(void *arg
* delete the session.
*/
l2cap_unregister_user(session->conn, &session->user);
+ hci_dev_put(session->conn->hcon->hdev);
hidp_session_put(session);

module_put_and_kthread_exit(0);
@@ -1378,6 +1379,7 @@ int hidp_connection_add(const struct hid
ret = l2cap_register_user(conn, &session->user);
if (ret)
goto out_session;
+ hci_dev_hold(conn->hcon->hdev);

ret = 0;

@@ -1405,8 +1407,10 @@ int hidp_connection_del(struct hidp_conn
HIDP_TRANS_HID_CONTROL |
HIDP_CTRL_VIRTUAL_CABLE_UNPLUG,
NULL, 0);
- else
+ else {
l2cap_unregister_user(session->conn, &session->user);
+ hci_dev_put(session->conn->hcon->hdev);
+ }

hidp_session_put(session);

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+14b6d5...@syzkaller.appspotmail.com
Tested-by: syzbot+14b6d5...@syzkaller.appspotmail.com

Tested on:

commit: c4264568 Merge tag 'acpi-6.12-rc6' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101af2a7980000

kernel config: https://syzkaller.appspot.com/x/.config?x=4340261e4e9f37fc
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=142ce187980000

Note: testing is done by a robot and is best-effort only.

[syzbot]

syzbot has bisected this issue to:

commit c8992cffbe7411c6da4c4416d5eecfc6b78e0fec
Author: Luiz Augusto von Dentz <luiz.vo...@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
start commit: 30b981796b94 selftests: drv-net: test empty queue and NAPI..
git tree: net
final oops: https://syzkaller.appspot.com/x/report.txt?x=16d538c4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12d538c4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6a2b862bf4a5409f
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12050adf980000

Reported-by: syzbot+14b6d5...@syzkaller.appspotmail.com
Fixes: c8992cffbe74 ("Bluetooth: hci_event: Use of a function table to handle Command Complete")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

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.vo...@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+14b6d5...@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
==================================================================


---

[Hillf Danton]

> Date: Tue, 12 Aug 2025 09:31:35 -0700 [thread overview]

> 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

> 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

#syz test

--- x/net/bluetooth/l2cap_core.c
+++ y/net/bluetooth/l2cap_core.c
@@ -1714,6 +1714,7 @@ int l2cap_register_user(struct l2cap_con

list_add(&user->list, &conn->users);
ret = 0;
+ hci_dev_hold(hdev);

out_unlock:
hci_dev_unlock(hdev);
@@ -1735,6 +1736,7 @@ void l2cap_unregister_user(struct l2cap_

out_unlock:
hci_dev_unlock(hdev);
+ hci_dev_put(hdev);
}
EXPORT_SYMBOL(l2cap_unregister_user);

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+14b6d5...@syzkaller.appspotmail.com
Tested-by: syzbot+14b6d5...@syzkaller.appspotmail.com

Tested on:

commit: 8f5ae30d 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=16786842580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=17f5caf0580000