[v6.1] KASAN: use-after-free Read in l2cap_sock_ready_cb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f2ddafa93a25 Linux 6.1.166
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12255552580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b1adc0bfde2d8a4a
dashboard link: https://syzkaller.appspot.com/bug?extid=0175fc2481dabf793baf
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15e83daa580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/28fc2cbac5cf/disk-f2ddafa9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b17a5a214fbc/vmlinux-f2ddafa9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c2564b1203e5/Image-f2ddafa9.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0175fc...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in l2cap_sock_ready_cb+0xc4/0x12c net/bluetooth/l2cap_sock.c:1714
Read of size 8 at addr ffff0000f0d9f4a8 by task kworker/1:0/4368

CPU: 1 PID: 4368 Comm: kworker/1:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/26/2026
Workqueue: events l2cap_info_timeout
Call trace:
dump_backtrace+0x1c0/0x1ec arch/arm64/kernel/stacktrace.c:158
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
__dump_stack+0x30/0x40 lib/dump_stack.c:88
dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
print_address_description+0x88/0x218 mm/kasan/report.c:316
print_report+0x50/0x68 mm/kasan/report.c:420
kasan_report+0xa8/0xfc mm/kasan/report.c:524
__asan_report_load8_noabort+0x2c/0x38 mm/kasan/report_generic.c:351
l2cap_sock_ready_cb+0xc4/0x12c net/bluetooth/l2cap_sock.c:1714
l2cap_chan_ready net/bluetooth/l2cap_core.c:1411 [inline]
l2cap_conn_start+0x5d4/0xb88 net/bluetooth/l2cap_core.c:1670
l2cap_info_timeout+0x68/0xb8 net/bluetooth/l2cap_core.c:1837
process_one_work+0x7f8/0x13a4 kernel/workqueue.c:2292
worker_thread+0x8c4/0xfec kernel/workqueue.c:2439
kthread+0x250/0x2d8 kernel/kthread.c:376
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

Allocated by task 12756:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
kasan_save_alloc_info+0x24/0x30 mm/kasan/generic.c:505
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0xa0/0xb8 mm/kasan/common.c:384
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slab_common.c:936 [inline]
__kmalloc+0xec/0x178 mm/slab_common.c:949
kmalloc include/linux/slab.h:568 [inline]
sk_prot_alloc+0xc4/0x1ec net/core/sock.c:2052
sk_alloc+0x44/0x390 net/core/sock.c:2108
bt_sock_alloc+0x4c/0x140 net/bluetooth/af_bluetooth.c:148
l2cap_sock_alloc net/bluetooth/l2cap_sock.c:1924 [inline]
l2cap_sock_create+0x140/0x2cc net/bluetooth/l2cap_sock.c:1966
bt_sock_create+0x14c/0x24c net/bluetooth/af_bluetooth.c:132
__sock_create+0x4b0/0x8b4 net/socket.c:1549
sock_create net/socket.c:1605 [inline]
__sys_socket_create net/socket.c:1642 [inline]
__sys_socket+0xc0/0x1ac net/socket.c:1670
__do_sys_socket net/socket.c:1683 [inline]
__se_sys_socket net/socket.c:1681 [inline]
__arm64_sys_socket+0x7c/0x94 net/socket.c:1681
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Freed by task 12755:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
kasan_save_free_info+0x38/0x5c mm/kasan/generic.c:516
____kasan_slab_free+0x148/0x1b0 mm/kasan/common.c:237
__kasan_slab_free+0x18/0x28 mm/kasan/common.c:245
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x16c/0x1e8 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
__kmem_cache_free+0xbc/0x218 mm/slub.c:3700
kfree+0xd0/0x1a8 mm/slab_common.c:988
sk_prot_free net/core/sock.c:2091 [inline]
__sk_destruct+0x4dc/0x76c net/core/sock.c:2177
sk_destruct net/core/sock.c:2192 [inline]
__sk_free+0x320/0x430 net/core/sock.c:2203
sk_free+0x60/0xc4 net/core/sock.c:2214
sock_put include/net/sock.h:2085 [inline]
l2cap_sock_kill+0x12c/0x22c net/bluetooth/l2cap_sock.c:1291
l2cap_sock_release+0x144/0x1bc net/bluetooth/l2cap_sock.c:1465
__sock_release net/socket.c:654 [inline]
sock_close+0xb4/0x1f8 net/socket.c:1399
__fput+0x1bc/0x7b8 fs/file_table.c:320
____fput+0x20/0x30 fs/file_table.c:348
task_work_run+0x1ec/0x278 kernel/task_work.c:203
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
do_notify_resume+0x1fa0/0x2aa4 arch/arm64/kernel/signal.c:1151
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

The buggy address belongs to the object at ffff0000f0d9f000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1192 bytes inside of
2048-byte region [ffff0000f0d9f000, ffff0000f0d9f800)

The buggy address belongs to the physical page:
page:00000000368d5ed0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x130d98
head:00000000368d5ed0 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000010200 dead000000000100 dead000000000122 ffff0000c0002900
raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000f0d9f380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000f0d9f400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000f0d9f480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000f0d9f500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000f0d9f580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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