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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d3d1556696c1 Merge tag 'mm-hotfixes-stable-2024-10-09-15-4..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1651a040580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fb6ea01107fa96bd
dashboard link: https://syzkaller.appspot.com/bug?extid=a1595e656a83ea5b78eb
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-d3d15566.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5087f167d7b8/vmlinux-d3d15566.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a9f5c056e452/bzImage-d3d15566.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a1595e...@syzkaller.appspotmail.com

Bluetooth: hci2: Controller not accepting commands anymore: ncmd = 0
Bluetooth: hci2: Injecting HCI hardware error event
Bluetooth: hci2: hardware error 0x00
==================================================================
BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0x1a6/0x1c0 lib/list_debug.c:62
Read of size 8 at addr ffff888048dd4550 by task kworker/u33:6/5358

CPU: 1 UID: 0 PID: 5358 Comm: kworker/u33:6 Not tainted 6.12.0-rc2-syzkaller-00074-gd3d1556696c1 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: hci2 hci_error_reset
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
__list_del_entry_valid_or_report+0x1a6/0x1c0 lib/list_debug.c:62
__list_del_entry_valid include/linux/list.h:124 [inline]
__list_del_entry include/linux/list.h:215 [inline]
list_del_init include/linux/list.h:287 [inline]
bt_accept_unlink+0x34/0x2e0 net/bluetooth/af_bluetooth.c:234
l2cap_sock_teardown_cb+0x1a3/0x3c0 net/bluetooth/l2cap_sock.c:1599
l2cap_chan_del+0xba/0x900 net/bluetooth/l2cap_core.c:658
l2cap_conn_del+0x37c/0x730 net/bluetooth/l2cap_core.c:1785
l2cap_disconn_cfm net/bluetooth/l2cap_core.c:7299 [inline]
l2cap_disconn_cfm+0x96/0xd0 net/bluetooth/l2cap_core.c:7292
hci_disconn_cfm include/net/bluetooth/hci_core.h:1975 [inline]
hci_conn_hash_flush+0x114/0x260 net/bluetooth/hci_conn.c:2589
hci_dev_close_sync+0x59e/0x1110 net/bluetooth/hci_sync.c:5195
hci_dev_do_close+0x2e/0x90 net/bluetooth/hci_core.c:483
hci_error_reset+0xbf/0x320 net/bluetooth/hci_core.c:1016
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
</TASK>

Allocated by task 6177:
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]
sk_prot_alloc+0x1a8/0x2a0 net/core/sock.c:2164
sk_alloc+0x36/0xb90 net/core/sock.c:2217
__netlink_create+0x5e/0x2c0 net/netlink/af_netlink.c:646
netlink_create+0x3a4/0x630 net/netlink/af_netlink.c:704
__sock_create+0x32e/0x800 net/socket.c:1576
sock_create net/socket.c:1627 [inline]
__sys_socket_create net/socket.c:1664 [inline]
__sys_socket+0x14f/0x260 net/socket.c:1711
__do_sys_socket net/socket.c:1725 [inline]
__se_sys_socket net/socket.c:1723 [inline]
__x64_sys_socket+0x72/0xb0 net/socket.c:1723
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 6182:
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
sk_prot_free net/core/sock.c:2200 [inline]
__sk_destruct+0x5eb/0x720 net/core/sock.c:2292
sk_destruct+0xc2/0xf0 net/core/sock.c:2307
__sk_free+0xf4/0x3e0 net/core/sock.c:2318
sk_free+0x6a/0x90 net/core/sock.c:2329
deferred_put_nlk_sk+0x13f/0x2d0 net/netlink/af_netlink.c:740
rcu_do_batch kernel/rcu/tree.c:2567 [inline]
rcu_core+0x79d/0x14d0 kernel/rcu/tree.c:2823
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:1037 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1037
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

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
__call_rcu_common.constprop.0+0x99/0x7a0 kernel/rcu/tree.c:3086
netlink_release+0x1206/0x1ff0 net/netlink/af_netlink.c:823
__sock_release+0xb0/0x270 net/socket.c:658
sock_close+0x1c/0x30 net/socket.c:1426
__fput+0x3f6/0xb60 fs/file_table.c:431
__fput_sync+0x45/0x50 fs/file_table.c:516
__do_sys_close fs/open.c:1565 [inline]
__se_sys_close fs/open.c:1550 [inline]
__x64_sys_close+0x86/0x100 fs/open.c:1550
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

The buggy address belongs to the object at ffff888048dd4000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1360 bytes inside of
freed 2048-byte region [ffff888048dd4000, ffff888048dd4800)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888048dd2000 pfn:0x48dd0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88801b042f00 ffffea00009c5e10 ffffea00012b8410
raw: ffff888048dd2000 0000000000080007 00000001f5000000 0000000000000000
head: 00fff00000000240 ffff88801b042f00 ffffea00009c5e10 ffffea00012b8410
head: ffff888048dd2000 0000000000080007 00000001f5000000 0000000000000000
head: 00fff00000000003 ffffea0001237401 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5352, tgid 5352 (syz-executor), ts 38680626357, free_ts 0
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]
rtnl_newlink+0x49/0xa0 net/core/rtnetlink.c:3739
rtnetlink_rcv_msg+0x3c7/0xea0 net/core/rtnetlink.c:6646
netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2550
netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1357
netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1901
sock_sendmsg_nosec net/socket.c:729 [inline]
__sock_sendmsg net/socket.c:744 [inline]
__sys_sendto+0x479/0x4d0 net/socket.c:2209
__do_sys_sendto net/socket.c:2221 [inline]
__se_sys_sendto net/socket.c:2217 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2217
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
page_owner free stack trace missing

Memory state around the buggy address:
ffff888048dd4400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888048dd4480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888048dd4500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888048dd4580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888048dd4600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: db9030a787e3 Merge remote-tracking branch 'will/for-next/p..
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=13645c12580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fdc83aa8a8b9d1ae
dashboard link: https://syzkaller.appspot.com/bug?extid=a1595e656a83ea5b78eb
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12cb37cd980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8932d8648ef5/disk-db9030a7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8446b6e4ef5c/vmlinux-db9030a7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b17118b94e44/Image-db9030a7.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a1595e...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0x8c/0x1b4 lib/list_debug.c:62
Read of size 8 at addr ffff0000f4f2f570 by task syz-executor/10110

CPU: 1 UID: 0 PID: 10110 Comm: syz-executor Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
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
__list_del_entry_valid_or_report+0x8c/0x1b4 lib/list_debug.c:62
__list_del_entry_valid include/linux/list.h:132 [inline]
__list_del_entry include/linux/list.h:223 [inline]
list_del_init include/linux/list.h:295 [inline]
bt_accept_unlink+0x40/0x248 net/bluetooth/af_bluetooth.c:259
l2cap_sock_teardown_cb+0x148/0x360 net/bluetooth/l2cap_sock.c:1616
l2cap_chan_del+0xb8/0x470 net/bluetooth/l2cap_core.c:655
l2cap_conn_del+0x2f8/0x5f0 net/bluetooth/l2cap_core.c:1787
l2cap_disconn_cfm+0x90/0xe0 net/bluetooth/l2cap_core.c:7325
hci_disconn_cfm include/net/bluetooth/hci_core.h:2122 [inline]
hci_conn_hash_flush+0x108/0x218 net/bluetooth/hci_conn.c:2609
hci_dev_close_sync+0x89c/0x1154 net/bluetooth/hci_sync.c:5308
hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
hci_unregister_dev+0x204/0x4c0 net/bluetooth/hci_core.c:2715
vhci_release+0x12c/0x17c drivers/bluetooth/hci_vhci.c:690
__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:966
do_group_exit+0x194/0x22c kernel/exit.c:1107
get_signal+0x11dc/0x12f8 kernel/signal.c:3034
arch_do_signal_or_restart+0x274/0x4414 arch/arm64/kernel/signal.c:1619
exit_to_user_mode_loop+0x7c/0x178 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:81 [inline]
el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:725
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Allocated by task 13304:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:77
kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:573
poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
__kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:417
kasan_kmalloc include/linux/kasan.h:262 [inline]
__do_kmalloc_node mm/slub.c:5646 [inline]
__kmalloc_noprof+0x3fc/0x728 mm/slub.c:5658
kmalloc_noprof include/linux/slab.h:961 [inline]
sk_prot_alloc+0xc4/0x1f0 net/core/sock.c:2239
sk_alloc+0x44/0x3ac net/core/sock.c:2295
pfkey_create+0xcc/0x520 net/key/af_key.c:152
__sock_create+0x43c/0x91c net/socket.c:1605
sock_create net/socket.c:1663 [inline]
__sys_socket_create net/socket.c:1700 [inline]
__sys_socket+0xd4/0x1c0 net/socket.c:1747
__do_sys_socket net/socket.c:1761 [inline]
__se_sys_socket net/socket.c:1759 [inline]
__arm64_sys_socket+0x7c/0x94 net/socket.c:1759
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 13304:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:77
__kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:587
kasan_save_free_info mm/kasan/kasan.h:406 [inline]
poison_slab_object mm/kasan/common.c:252 [inline]
__kasan_slab_free+0x74/0xa4 mm/kasan/common.c:284
kasan_slab_free include/linux/kasan.h:234 [inline]
slab_free_hook mm/slub.c:2539 [inline]
slab_free mm/slub.c:6634 [inline]
kfree+0x184/0x600 mm/slub.c:6841
sk_prot_free net/core/sock.c:2278 [inline]
__sk_destruct+0x514/0x780 net/core/sock.c:2373
sk_destruct net/core/sock.c:2401 [inline]
__sk_free+0x320/0x430 net/core/sock.c:2412
sk_free+0x60/0xc8 net/core/sock.c:2423
sock_put include/net/sock.h:1972 [inline]
pfkey_release+0x254/0x338 net/key/af_key.c:186
__sock_release net/socket.c:662 [inline]
sock_close+0xa0/0x1e4 net/socket.c:1455
__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
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xfc/0x178 kernel/entry/common.c:43
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:81 [inline]
el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:725
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

The buggy address belongs to the object at ffff0000f4f2f000

which belongs to the cache kmalloc-2k of size 2048

The buggy address is located 1392 bytes inside of
freed 2048-byte region [ffff0000f4f2f000, ffff0000f4f2f800)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x134f28

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 ffff0000c0002000 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000080008 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c0002000 0000000000000000 dead000000000001
head: 0000000000000000 0000000000080008 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc3d3ca01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff0000f4f2f400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000f4f2f480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000f4f2f500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000f4f2f580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000f4f2f600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
slab kmalloc-2k start ffff0000f4f2f000 pointer offset 1392 size 2048
list_del corruption. prev->next should be ffff0000d9262570, but was 0000000000000000. (prev=ffff0000f4f2f570)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:64!
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
Modules linked in:
CPU: 1 UID: 0 PID: 10110 Comm: syz-executor Tainted: G B syzkaller #0 PREEMPT
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 63400005 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __list_del_entry_valid_or_report+0x17c/0x1b4 lib/list_debug.c:62
lr : __list_del_entry_valid_or_report+0x17c/0x1b4 lib/list_debug.c:62
sp : ffff80009bed7370
x29: ffff80009bed7370 x28: 0000000000000003 x27: ffff0000f6f3e00c
x26: ffff0000f6f3e000 x25: 1fffe0001ede7c02 x24: dfff800000000000
x23: 1fffe0001e9e5eae x22: dfff800000000000 x21: ffff0000f4f2f570
x20: ffff0000f4f2f570 x19: ffff0000d9262570 x18: 1fffe000337dfe90
x17: 20747562202c3037 x16: ffff800082debe40 x15: 0000000000000001
x14: 1fffe000337dfefa x13: 0000000000000000 x12: 0000000000000000
x11: ffff6000337dfefb x10: 0000000000ff0100 x9 : 6db35dbdbd571600
x8 : 6db35dbdbd571600 x7 : fffffffffffce210 x6 : ffff8000805653c0
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000807d6608
x2 : 0000000000000001 x1 : 0000000100000000 x0 : 000000000000006d
Call trace:
__list_del_entry_valid_or_report+0x17c/0x1b4 lib/list_debug.c:62 (P)
__list_del_entry_valid include/linux/list.h:132 [inline]
__list_del_entry include/linux/list.h:223 [inline]
list_del_init include/linux/list.h:295 [inline]
bt_accept_unlink+0x40/0x248 net/bluetooth/af_bluetooth.c:259
l2cap_sock_teardown_cb+0x148/0x360 net/bluetooth/l2cap_sock.c:1616
l2cap_chan_del+0xb8/0x470 net/bluetooth/l2cap_core.c:655
l2cap_conn_del+0x2f8/0x5f0 net/bluetooth/l2cap_core.c:1787
l2cap_disconn_cfm+0x90/0xe0 net/bluetooth/l2cap_core.c:7325
hci_disconn_cfm include/net/bluetooth/hci_core.h:2122 [inline]
hci_conn_hash_flush+0x108/0x218 net/bluetooth/hci_conn.c:2609
hci_dev_close_sync+0x89c/0x1154 net/bluetooth/hci_sync.c:5308
hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
hci_unregister_dev+0x204/0x4c0 net/bluetooth/hci_core.c:2715
vhci_release+0x12c/0x17c drivers/bluetooth/hci_vhci.c:690
__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:966
do_group_exit+0x194/0x22c kernel/exit.c:1107
get_signal+0x11dc/0x12f8 kernel/signal.c:3034
arch_do_signal_or_restart+0x274/0x4414 arch/arm64/kernel/signal.c:1619
exit_to_user_mode_loop+0x7c/0x178 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:81 [inline]
el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:725
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
Code: 910d0000 aa1303e1 aa1503e3 974c6749 (d4210000)
---[ end trace 0000000000000000 ]---


---
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.

[Hillf Danton]

> Date: Fri, 14 Nov 2025 15:12:26 -0800

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: db9030a787e3 Merge remote-tracking branch 'will/for-next/p..
> 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=13645c12580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=fdc83aa8a8b9d1ae
> dashboard link: https://syzkaller.appspot.com/bug?extid=a1595e656a83ea5b78eb
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> userspace arch: arm64
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12cb37cd980000

#syz test

--- x/net/bluetooth/af_bluetooth.c
+++ y/net/bluetooth/af_bluetooth.c
@@ -256,6 +256,8 @@ void bt_accept_unlink(struct sock *sk)
{
BT_DBG("sk %p state %d", sk, sk->sk_state);

+ if (bt_sk(sk)->parent == NULL)
+ return;
list_del_init(&bt_sk(sk)->accept_q);
sk_acceptq_removed(bt_sk(sk)->parent);
bt_sk(sk)->parent = NULL;
--- x/net/bluetooth/l2cap_sock.c
+++ y/net/bluetooth/l2cap_sock.c
@@ -1581,6 +1581,7 @@ static void l2cap_sock_teardown_cb(struc

if (!sk)
return;
+ sock_hold(sk);

BT_DBG("chan %p state %s", chan, state_to_string(chan->state));

@@ -1613,8 +1614,14 @@ static void l2cap_sock_teardown_cb(struc
sk->sk_err = err;

if (parent) {
+ sock_hold(parent);
+ release_sock(sk);
+ lock_sock(parent);
bt_accept_unlink(sk);
+ release_sock(parent);
parent->sk_data_ready(parent);
+ sock_put(parent);
+ goto zap;
} else {
sk->sk_state_change(sk);
}
@@ -1623,9 +1630,10 @@ static void l2cap_sock_teardown_cb(struc
}
release_sock(sk);

+zap:
/* Only zap after cleanup to avoid use after free race */
sock_set_flag(sk, SOCK_ZAPPED);
-
+ sock_put(sk);
}

static void l2cap_sock_state_change_cb(struct l2cap_chan *chan, int state,
--

[syzbot]

Hello,

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

Reported-by: syzbot+a1595e...@syzkaller.appspotmail.com
Tested-by: syzbot+a1595e...@syzkaller.appspotmail.com

Tested on:

commit: db9030a7 Merge remote-tracking branch 'will/for-next/p..

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=159fa884580000

kernel config: https://syzkaller.appspot.com/x/.config?x=fdc83aa8a8b9d1ae
dashboard link: https://syzkaller.appspot.com/bug?extid=a1595e656a83ea5b78eb
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

patch: https://syzkaller.appspot.com/x/patch.diff?x=11ec5c12580000

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