Bluetooth: L2CAP: Fix uaf in l2cap_connect

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: L2CAP: Fix uaf in l2cap_connect

[Syzbot reported]
BUG: KASAN: slab-use-after-free in l2cap_connect.constprop.0+0x10d8/0x1270 net/bluetooth/l2cap_core.c:3949
Read of size 8 at addr ffff8880241e9800 by task kworker/u9:0/54

CPU: 0 UID: 0 PID: 54 Comm: kworker/u9:0 Not tainted 6.11.0-rc6-syzkaller-00268-g788220eee30d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: hci2 hci_rx_work
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:93 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
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
l2cap_connect.constprop.0+0x10d8/0x1270 net/bluetooth/l2cap_core.c:3949
l2cap_connect_req net/bluetooth/l2cap_core.c:4080 [inline]
l2cap_bredr_sig_cmd net/bluetooth/l2cap_core.c:4772 [inline]
l2cap_sig_channel net/bluetooth/l2cap_core.c:5543 [inline]
l2cap_recv_frame+0xf0b/0x8eb0 net/bluetooth/l2cap_core.c:6825
l2cap_recv_acldata+0x9b4/0xb70 net/bluetooth/l2cap_core.c:7514
hci_acldata_packet net/bluetooth/hci_core.c:3791 [inline]
hci_rx_work+0xaab/0x1610 net/bluetooth/hci_core.c:4028
process_one_work+0x9c5/0x1b40 kernel/workqueue.c:3231
process_scheduled_works kernel/workqueue.c:3312 [inline]
worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
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
...

Freed by task 5245:
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+0xf7/0x160 mm/kasan/common.c:240
__kasan_slab_free+0x32/0x50 mm/kasan/common.c:256
kasan_slab_free include/linux/kasan.h:184 [inline]
slab_free_hook mm/slub.c:2256 [inline]
slab_free mm/slub.c:4477 [inline]
kfree+0x12a/0x3b0 mm/slub.c:4598
l2cap_conn_free net/bluetooth/l2cap_core.c:1810 [inline]
kref_put include/linux/kref.h:65 [inline]
l2cap_conn_put net/bluetooth/l2cap_core.c:1822 [inline]
l2cap_conn_del+0x59d/0x730 net/bluetooth/l2cap_core.c:1802
l2cap_connect_cfm+0x9e6/0xf80 net/bluetooth/l2cap_core.c:7241
hci_connect_cfm include/net/bluetooth/hci_core.h:1960 [inline]
hci_conn_failed+0x1c3/0x370 net/bluetooth/hci_conn.c:1265
hci_abort_conn_sync+0x75a/0xb50 net/bluetooth/hci_sync.c:5583
abort_conn_sync+0x197/0x360 net/bluetooth/hci_conn.c:2917
hci_cmd_sync_work+0x1a4/0x410 net/bluetooth/hci_sync.c:328
process_one_work+0x9c5/0x1b40 kernel/workqueue.c:3231
process_scheduled_works kernel/workqueue.c:3312 [inline]
worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
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