[v6.1] KASAN: slab-out-of-bounds Read in bt_accept_unlink

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50cbba13faa2 Linux 6.1.159
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13a0849a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6a5cbd268406bf43
dashboard link: https://syzkaller.appspot.com/bug?extid=0234d971a151c4e17b8e
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/50ceb00b1b39/disk-50cbba13.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ebb8883b9a29/vmlinux-50cbba13.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7edc2a795f03/bzImage-50cbba13.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0234d9...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in __list_del_entry_valid+0x80/0x120 lib/list_debug.c:59
Read of size 8 at addr ffff88802370c518 by task syz-executor/4274

CPU: 0 PID: 4274 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
print_address_description mm/kasan/report.c:316 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:420
kasan_report+0x10b/0x140 mm/kasan/report.c:524
__list_del_entry_valid+0x80/0x120 lib/list_debug.c:59
__list_del_entry include/linux/list.h:134 [inline]
list_del_init include/linux/list.h:206 [inline]
bt_accept_unlink+0x35/0x230 net/bluetooth/af_bluetooth.c:232
l2cap_sock_teardown_cb+0x1af/0x380 net/bluetooth/l2cap_sock.c:1636
l2cap_chan_del+0xab/0x620 net/bluetooth/l2cap_core.c:680
l2cap_conn_del+0x3c4/0x6a0 net/bluetooth/l2cap_core.c:1955
hci_disconn_cfm include/net/bluetooth/hci_core.h:1829 [inline]
hci_conn_hash_flush+0x113/0x290 net/bluetooth/hci_conn.c:2504
hci_dev_close_sync+0x930/0xf40 net/bluetooth/hci_sync.c:5246
hci_dev_do_close net/bluetooth/hci_core.c:510 [inline]
hci_unregister_dev+0x202/0x4f0 net/bluetooth/hci_core.c:2705
vhci_release+0x7f/0xd0 drivers/bluetooth/hci_vhci.c:573
__fput+0x22c/0x920 fs/file_table.c:320
task_work_run+0x1ca/0x250 kernel/task_work.c:203
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0x93e/0x2400 kernel/exit.c:880
do_group_exit+0x217/0x2d0 kernel/exit.c:1022
__do_sys_exit_group kernel/exit.c:1033 [inline]
__se_sys_exit_group kernel/exit.c:1031 [inline]
__x64_sys_exit_group+0x3b/0x40 kernel/exit.c:1031
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f40ae98f749
Code: Unable to access opcode bytes at 0x7f40ae98f71f.
RSP: 002b:00007ffe3989d2c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f40aea13da2 RCX: 00007f40ae98f749
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 0000000000000002 R08: 00007ffe3989b067 R09: 00007ffe3989e580
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe3989e580
R13: 00007f40aea13d7d R14: 000000000003e282 R15: 00007ffe3989f650
</TASK>

Allocated by task 6918:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:383
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slab_common.c:936 [inline]
__kmalloc+0xb0/0x240 mm/slab_common.c:949
kmalloc include/linux/slab.h:568 [inline]
kmem_alloc+0x15e/0x480 fs/xfs/kmem.c:20
kmem_zalloc fs/xfs/kmem.h:69 [inline]
xlog_alloc_log+0x2d/0x1400 fs/xfs/xfs_log.c:1529
xfs_log_mount+0xc8/0x460 fs/xfs/xfs_log.c:655
xfs_mountfs+0xc42/0x1d10 fs/xfs/xfs_mount.c:819
xfs_fs_fill_super+0x10f0/0x1350 fs/xfs/xfs_super.c:1690
get_tree_bdev+0x3f1/0x610 fs/super.c:1366
vfs_get_tree+0x88/0x270 fs/super.c:1573
do_new_mount+0x24a/0xa40 fs/namespace.c:3078
do_mount fs/namespace.c:3421 [inline]
__do_sys_mount fs/namespace.c:3629 [inline]
__se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3606
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88802370c000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1304 bytes inside of
2048-byte region [ffff88802370c000, ffff88802370c800)

The buggy address belongs to the physical page:
page:ffffea00008dc200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x23708
head:ffffea00008dc200 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001660e00 dead000000000002 ffff888017442000
raw: 0000000000000000 0000000000080008 00000001ffffffff 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 4274, tgid 4274 (syz-executor), ts 76688748644, free_ts 76687354118
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2532
prep_new_page mm/page_alloc.c:2539 [inline]
get_page_from_freelist+0x1a26/0x1ac0 mm/page_alloc.c:4328
__alloc_pages+0x1df/0x4e0 mm/page_alloc.c:5614
alloc_slab_page+0x5d/0x160 mm/slub.c:1799
allocate_slab mm/slub.c:1944 [inline]
new_slab+0x87/0x2c0 mm/slub.c:1997
___slab_alloc+0xbc6/0x1230 mm/slub.c:3154
__slab_alloc mm/slub.c:3240 [inline]
slab_alloc_node mm/slub.c:3325 [inline]
__kmem_cache_alloc_node+0x1a0/0x260 mm/slub.c:3398
__do_kmalloc_node mm/slab_common.c:935 [inline]
__kmalloc_node_track_caller+0x9e/0x230 mm/slab_common.c:956
kmalloc_reserve net/core/skbuff.c:446 [inline]
__alloc_skb+0x22a/0x7e0 net/core/skbuff.c:515
alloc_skb include/linux/skbuff.h:1271 [inline]
nlmsg_new include/net/netlink.h:991 [inline]
rtmsg_ifinfo_build_skb+0x80/0x180 net/core/rtnetlink.c:3966
rtmsg_ifinfo_event net/core/rtnetlink.c:4002 [inline]
rtmsg_ifinfo+0x71/0x120 net/core/rtnetlink.c:4011
register_netdevice+0x16fb/0x1aa0 net/core/dev.c:10251
__ip_tunnel_create+0x33e/0x440 net/ipv4/ip_tunnel.c:267
ip_tunnel_init_net+0x28f/0x740 net/ipv4/ip_tunnel.c:1104
ops_init+0x355/0x5f0 net/core/net_namespace.c:138
setup_net+0x4e1/0xbb0 net/core/net_namespace.c:336
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1459 [inline]
free_pcp_prepare mm/page_alloc.c:1509 [inline]
free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3384
free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3479
qlink_free mm/kasan/quarantine.c:168 [inline]
qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
__kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:305
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
slab_alloc_node mm/slub.c:3359 [inline]
__kmem_cache_alloc_node+0x140/0x260 mm/slub.c:3398
kmalloc_trace+0x26/0xe0 mm/slab_common.c:1026
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
ref_tracker_alloc+0x129/0x450 lib/ref_tracker.c:85
register_netdevice+0x14ae/0x1aa0 net/core/dev.c:10224
__ip_tunnel_create+0x33e/0x440 net/ipv4/ip_tunnel.c:267
ip_tunnel_init_net+0x28f/0x740 net/ipv4/ip_tunnel.c:1104
ops_init+0x355/0x5f0 net/core/net_namespace.c:138
setup_net+0x4e1/0xbb0 net/core/net_namespace.c:336
copy_net_ns+0x348/0x5b0 net/core/net_namespace.c:508
create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110

Memory state around the buggy address:
ffff88802370c400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88802370c480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff88802370c500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88802370c580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802370c600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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