KASAN: use-after-free in __mutex_lock

Posted by Sungwoo Kim 3 years, 7 months ago

Hello, I am Sungwoo Kim (https://sung-woo.kim) from Purdue University.

We report a bug found by FuzzBT, a modified version of syzkaller.
It looks similar to the recent bug:
https://lore.kernel.org/lkml/20220622082716.478486-1-lee.jones@linaro.org

We propose to add l2cap_chan_hold_unless_zero() for after calling
__l2cap_get_chan_blah().

Bluetooth: l2cap_core.c:static void l2cap_chan_destroy(struct kref *kref)
Bluetooth: chan 0000000023c4974d
Bluetooth: parent 00000000ae861c08
==================================================================
BUG: KASAN: use-after-free in __mutex_waiter_is_first
kernel/locking/mutex.c:191 [inline]
BUG: KASAN: use-after-free in __mutex_lock_common
kernel/locking/mutex.c:671 [inline]
BUG: KASAN: use-after-free in __mutex_lock+0x278/0x400
kernel/locking/mutex.c:729
Read of size 8 at addr ffff888006a49b08 by task kworker/u3:2/389

CPU: 0 PID: 389 Comm: kworker/u3:2 Not tainted 5.15.0 #14
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Workqueue: hci0 hci_rx_work
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x7e/0xb7 lib/dump_stack.c:106
 print_address_description+0x88/0x3b0 mm/kasan/report.c:256
 __kasan_report mm/kasan/report.c:442 [inline]
 kasan_report+0x172/0x1c0 mm/kasan/report.c:459
 __asan_load8+0x80/0x90 mm/kasan/generic.c:256
 __mutex_waiter_is_first kernel/locking/mutex.c:191 [inline]
 __mutex_lock_common kernel/locking/mutex.c:671 [inline]
 __mutex_lock+0x278/0x400 kernel/locking/mutex.c:729
 __mutex_lock_slowpath+0x13/0x20 kernel/locking/mutex.c:979
 mutex_lock+0x91/0xf0 kernel/locking/mutex.c:280
 l2cap_chan_lock include/net/bluetooth/l2cap.h:890 [inline]
 l2cap_connect_create_rsp net/bluetooth/l2cap_core.c:4431 [inline]
 l2cap_bredr_sig_cmd+0xc7c/0x4060 net/bluetooth/l2cap_core.c:5865
 l2cap_sig_channel net/bluetooth/l2cap_core.c:6633 [inline]
 l2cap_recv_frame+0x71e/0xa00 net/bluetooth/l2cap_core.c:7899
 l2cap_recv_acldata+0x3a2/0x6c0 net/bluetooth/l2cap_core.c:8641
 hci_acldata_packet net/bluetooth/hci_core.c:5100 [inline]
 hci_rx_work+0x39c/0x500 net/bluetooth/hci_core.c:5307
 process_one_work+0x28c/0x440 kernel/workqueue.c:2297
 worker_thread+0x434/0x5d0 kernel/workqueue.c:2444
 kthread+0x214/0x250 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

Allocated by task 389:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc+0xd6/0x110 mm/kasan/common.c:513
 __kasan_kmalloc+0x9/0x10 mm/kasan/common.c:522
 kasan_kmalloc include/linux/kasan.h:264 [inline]
 kmem_cache_alloc_trace+0x1a9/0x230 mm/slub.c:3240
 kmalloc include/linux/slab.h:591 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 l2cap_chan_create+0x4c/0x2c0 net/bluetooth/l2cap_core.c:481
 l2cap_sock_alloc+0xfa/0x150 net/bluetooth/l2cap_sock.c:1867
 l2cap_sock_new_connection_cb+0xc9/0x140 net/bluetooth/l2cap_sock.c:1467
 l2cap_connect+0x3eb/0x850 net/bluetooth/l2cap_core.c:4274
 l2cap_connect_req net/bluetooth/l2cap_core.c:4387 [inline]
 l2cap_bredr_sig_cmd+0x13fd/0x4060 net/bluetooth/l2cap_core.c:5860
 l2cap_sig_channel net/bluetooth/l2cap_core.c:6633 [inline]
 l2cap_recv_frame+0x71e/0xa00 net/bluetooth/l2cap_core.c:7899
 l2cap_recv_acldata+0x3a2/0x6c0 net/bluetooth/l2cap_core.c:8641
 hci_acldata_packet net/bluetooth/hci_core.c:5100 [inline]
 hci_rx_work+0x39c/0x500 net/bluetooth/hci_core.c:5307
 process_one_work+0x28c/0x440 kernel/workqueue.c:2297
 worker_thread+0x434/0x5d0 kernel/workqueue.c:2444
 kthread+0x214/0x250 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

Freed by task 364:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x3d/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0x13a/0x170 mm/kasan/common.c:366
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1700 [inline]
 slab_free_freelist_hook+0x100/0x1a0 mm/slub.c:1726
 slab_free mm/slub.c:3492 [inline]
 kfree+0xe0/0x270 mm/slub.c:4552
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:524 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x147/0x190 net/bluetooth/l2cap_core.c:540
 l2cap_sock_cleanup_listen net/bluetooth/l2cap_sock.c:1449 [inline]
 l2cap_sock_teardown_cb+0x33a/0x3e0 net/bluetooth/l2cap_sock.c:1564
 l2cap_chan_close+0x297/0x640
 l2cap_sock_shutdown+0x6cc/0x8b0 net/bluetooth/l2cap_sock.c:1367
 l2cap_sock_release+0x7d/0x130 net/bluetooth/l2cap_sock.c:1411
 __sock_release+0x80/0x170 net/socket.c:649
 sock_close+0x1e/0x30 net/socket.c:1314
 __fput+0x2de/0x5d0 fs/file_table.c:280
 ____fput+0x1a/0x20 fs/file_table.c:313
 task_work_run+0x102/0x150 kernel/task_work.c:164
 exit_task_work include/linux/task_work.h:32 [inline]
 do_exit+0x511/0x1260 kernel/exit.c:825
 do_group_exit+0xd9/0x1a0 kernel/exit.c:922
 get_signal+0x397/0x11a0 kernel/signal.c:2855
 arch_do_signal_or_restart+0x3b/0x3b0 arch/x86/kernel/signal.c:865
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x103/0x1a0 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x2a/0x40 kernel/entry/common.c:300
 do_syscall_64+0x52/0xc0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888006a49800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 776 bytes inside of
 1024-byte region [ffff888006a49800, ffff888006a49c00)
The buggy address belongs to the page:
page:000000004d4d912c refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x6a48
head:000000004d4d912c order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfffffc0010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0010200 dead000000000100 dead000000000122 ffff888001041dc0
raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888006a49a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888006a49a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888006a49b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888006a49b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888006a49c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 2c9de67da..0e7978228 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4309,7 +4309,10 @@ static int l2cap_connect_create_rsp(struct
l2cap_conn *conn,

        err = 0;

-       l2cap_chan_lock(chan);
+       chan = l2cap_chan_hold_unless_zero(chan);
+       if (chan) {
+               l2cap_chan_lock(chan);
+       }

        switch (result) {
        case L2CAP_CR_SUCCESS:
@@ -4336,6 +4339,7 @@ static int l2cap_connect_create_rsp(struct
l2cap_conn *conn,
        }

        l2cap_chan_unlock(chan);
+       l2cap_chan_put(chan);

 unlock:
        mutex_unlock(&conn->chan_lock);


Best regards,
Sungwoo Kim.

Re: KASAN: use-after-free in __mutex_lock

Posted by Luiz Augusto von Dentz 3 years, 6 months ago

Hi Kim,

On Sat, Sep 3, 2022 at 1:09 PM Sungwoo Kim <iam@sung-woo.kim> wrote:
>
> Hello, I am Sungwoo Kim (https://sung-woo.kim) from Purdue University.
>
> We report a bug found by FuzzBT, a modified version of syzkaller.
> It looks similar to the recent bug:
> https://lore.kernel.org/lkml/20220622082716.478486-1-lee.jones@linaro.org
>
> We propose to add l2cap_chan_hold_unless_zero() for after calling
> __l2cap_get_chan_blah().
>
> Bluetooth: l2cap_core.c:static void l2cap_chan_destroy(struct kref *kref)
> Bluetooth: chan 0000000023c4974d
> Bluetooth: parent 00000000ae861c08
> ==================================================================
> BUG: KASAN: use-after-free in __mutex_waiter_is_first
> kernel/locking/mutex.c:191 [inline]
> BUG: KASAN: use-after-free in __mutex_lock_common
> kernel/locking/mutex.c:671 [inline]
> BUG: KASAN: use-after-free in __mutex_lock+0x278/0x400
> kernel/locking/mutex.c:729
> Read of size 8 at addr ffff888006a49b08 by task kworker/u3:2/389
>
> CPU: 0 PID: 389 Comm: kworker/u3:2 Not tainted 5.15.0 #14
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.13.0-1ubuntu1.1 04/01/2014
> Workqueue: hci0 hci_rx_work
> Call Trace:
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x7e/0xb7 lib/dump_stack.c:106
>  print_address_description+0x88/0x3b0 mm/kasan/report.c:256
>  __kasan_report mm/kasan/report.c:442 [inline]
>  kasan_report+0x172/0x1c0 mm/kasan/report.c:459
>  __asan_load8+0x80/0x90 mm/kasan/generic.c:256
>  __mutex_waiter_is_first kernel/locking/mutex.c:191 [inline]
>  __mutex_lock_common kernel/locking/mutex.c:671 [inline]
>  __mutex_lock+0x278/0x400 kernel/locking/mutex.c:729
>  __mutex_lock_slowpath+0x13/0x20 kernel/locking/mutex.c:979
>  mutex_lock+0x91/0xf0 kernel/locking/mutex.c:280
>  l2cap_chan_lock include/net/bluetooth/l2cap.h:890 [inline]
>  l2cap_connect_create_rsp net/bluetooth/l2cap_core.c:4431 [inline]
>  l2cap_bredr_sig_cmd+0xc7c/0x4060 net/bluetooth/l2cap_core.c:5865
>  l2cap_sig_channel net/bluetooth/l2cap_core.c:6633 [inline]
>  l2cap_recv_frame+0x71e/0xa00 net/bluetooth/l2cap_core.c:7899
>  l2cap_recv_acldata+0x3a2/0x6c0 net/bluetooth/l2cap_core.c:8641
>  hci_acldata_packet net/bluetooth/hci_core.c:5100 [inline]
>  hci_rx_work+0x39c/0x500 net/bluetooth/hci_core.c:5307
>  process_one_work+0x28c/0x440 kernel/workqueue.c:2297
>  worker_thread+0x434/0x5d0 kernel/workqueue.c:2444
>  kthread+0x214/0x250 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30
>
> Allocated by task 389:
>  kasan_save_stack mm/kasan/common.c:38 [inline]
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:434 [inline]
>  ____kasan_kmalloc+0xd6/0x110 mm/kasan/common.c:513
>  __kasan_kmalloc+0x9/0x10 mm/kasan/common.c:522
>  kasan_kmalloc include/linux/kasan.h:264 [inline]
>  kmem_cache_alloc_trace+0x1a9/0x230 mm/slub.c:3240
>  kmalloc include/linux/slab.h:591 [inline]
>  kzalloc include/linux/slab.h:721 [inline]
>  l2cap_chan_create+0x4c/0x2c0 net/bluetooth/l2cap_core.c:481
>  l2cap_sock_alloc+0xfa/0x150 net/bluetooth/l2cap_sock.c:1867
>  l2cap_sock_new_connection_cb+0xc9/0x140 net/bluetooth/l2cap_sock.c:1467
>  l2cap_connect+0x3eb/0x850 net/bluetooth/l2cap_core.c:4274
>  l2cap_connect_req net/bluetooth/l2cap_core.c:4387 [inline]
>  l2cap_bredr_sig_cmd+0x13fd/0x4060 net/bluetooth/l2cap_core.c:5860
>  l2cap_sig_channel net/bluetooth/l2cap_core.c:6633 [inline]
>  l2cap_recv_frame+0x71e/0xa00 net/bluetooth/l2cap_core.c:7899
>  l2cap_recv_acldata+0x3a2/0x6c0 net/bluetooth/l2cap_core.c:8641
>  hci_acldata_packet net/bluetooth/hci_core.c:5100 [inline]
>  hci_rx_work+0x39c/0x500 net/bluetooth/hci_core.c:5307
>  process_one_work+0x28c/0x440 kernel/workqueue.c:2297
>  worker_thread+0x434/0x5d0 kernel/workqueue.c:2444
>  kthread+0x214/0x250 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30
>
> Freed by task 364:
>  kasan_save_stack mm/kasan/common.c:38 [inline]
>  kasan_set_track+0x3d/0x70 mm/kasan/common.c:46
>  kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:360
>  ____kasan_slab_free+0x13a/0x170 mm/kasan/common.c:366
>  __kasan_slab_free+0x11/0x20 mm/kasan/common.c:374
>  kasan_slab_free include/linux/kasan.h:230 [inline]
>  slab_free_hook mm/slub.c:1700 [inline]
>  slab_free_freelist_hook+0x100/0x1a0 mm/slub.c:1726
>  slab_free mm/slub.c:3492 [inline]
>  kfree+0xe0/0x270 mm/slub.c:4552
>  l2cap_chan_destroy net/bluetooth/l2cap_core.c:524 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  l2cap_chan_put+0x147/0x190 net/bluetooth/l2cap_core.c:540
>  l2cap_sock_cleanup_listen net/bluetooth/l2cap_sock.c:1449 [inline]
>  l2cap_sock_teardown_cb+0x33a/0x3e0 net/bluetooth/l2cap_sock.c:1564
>  l2cap_chan_close+0x297/0x640
>  l2cap_sock_shutdown+0x6cc/0x8b0 net/bluetooth/l2cap_sock.c:1367
>  l2cap_sock_release+0x7d/0x130 net/bluetooth/l2cap_sock.c:1411
>  __sock_release+0x80/0x170 net/socket.c:649
>  sock_close+0x1e/0x30 net/socket.c:1314
>  __fput+0x2de/0x5d0 fs/file_table.c:280
>  ____fput+0x1a/0x20 fs/file_table.c:313
>  task_work_run+0x102/0x150 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0x511/0x1260 kernel/exit.c:825
>  do_group_exit+0xd9/0x1a0 kernel/exit.c:922
>  get_signal+0x397/0x11a0 kernel/signal.c:2855
>  arch_do_signal_or_restart+0x3b/0x3b0 arch/x86/kernel/signal.c:865
>  handle_signal_work kernel/entry/common.c:148 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>  exit_to_user_mode_prepare+0x103/0x1a0 kernel/entry/common.c:207
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
>  syscall_exit_to_user_mode+0x2a/0x40 kernel/entry/common.c:300
>  do_syscall_64+0x52/0xc0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff888006a49800
>  which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 776 bytes inside of
>  1024-byte region [ffff888006a49800, ffff888006a49c00)
> The buggy address belongs to the page:
> page:000000004d4d912c refcount:1 mapcount:0 mapping:0000000000000000
> index:0x0 pfn:0x6a48
> head:000000004d4d912c order:2 compound_mapcount:0 compound_pincount:0
> flags: 0xfffffc0010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff)
> raw: 000fffffc0010200 dead000000000100 dead000000000122 ffff888001041dc0
> raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff888006a49a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888006a49a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff888006a49b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                       ^
>  ffff888006a49b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888006a49c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c9de67da..0e7978228 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -4309,7 +4309,10 @@ static int l2cap_connect_create_rsp(struct
> l2cap_conn *conn,
>
>         err = 0;
>
> -       l2cap_chan_lock(chan);
> +       chan = l2cap_chan_hold_unless_zero(chan);
> +       if (chan) {
> +               l2cap_chan_lock(chan);
> +       }

This obviously doesn't work since you will need to bail out if chan is
NULL, so we would need to do something like:

if (!chan) {
  err = -EBADSLT;
  goto unlock;
}

l2cap_chan_lock(chan);

>
>         switch (result) {
>         case L2CAP_CR_SUCCESS:
> @@ -4336,6 +4339,7 @@ static int l2cap_connect_create_rsp(struct
> l2cap_conn *conn,
>         }
>
>         l2cap_chan_unlock(chan);
> +       l2cap_chan_put(chan);
>
>  unlock:
>         mutex_unlock(&conn->chan_lock);
>
>
> Best regards,
> Sungwoo Kim.



-- 
Luiz Augusto von Dentz

Re: KASAN: use-after-free in __mutex_lock

Posted by Sungwoo Kim 3 years, 6 months ago

Hi Dentz,
How about to use l2cap_get_chan_by_scid because it looks resposible to
handle ref_cnt.

Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
---
 net/bluetooth/l2cap_core.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 2c9de67da..d3a074cbc 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4291,26 +4291,18 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 	BT_DBG("dcid 0x%4.4x scid 0x%4.4x result 0x%2.2x status 0x%2.2x",
 	       dcid, scid, result, status);
 
-	mutex_lock(&conn->chan_lock);
-
 	if (scid) {
-		chan = __l2cap_get_chan_by_scid(conn, scid);
-		if (!chan) {
-			err = -EBADSLT;
-			goto unlock;
-		}
+		chan = l2cap_get_chan_by_scid(conn, scid);
+		if (!chan)
+			return -EBADSLT;
 	} else {
-		chan = __l2cap_get_chan_by_ident(conn, cmd->ident);
-		if (!chan) {
-			err = -EBADSLT;
-			goto unlock;
-		}
+		chan = l2cap_get_chan_by_ident(conn, cmd->ident);
+		if (!chan)
+			return -EBADSLT;
 	}
 
 	err = 0;
 
-	l2cap_chan_lock(chan);
-
 	switch (result) {
 	case L2CAP_CR_SUCCESS:
 		l2cap_state_change(chan, BT_CONFIG);
@@ -4336,9 +4328,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 	}
 
 	l2cap_chan_unlock(chan);
-
-unlock:
-	mutex_unlock(&conn->chan_lock);
+	l2cap_chan_put(chan);
 
 	return err;
 }
-- 
2.25.1

Re: KASAN: use-after-free in __mutex_lock

Posted by Luiz Augusto von Dentz 3 years, 6 months ago

Hi Kim,

On Fri, Sep 30, 2022 at 9:09 AM Sungwoo Kim <iam@sung-woo.kim> wrote:
>
> Hi Dentz,
> How about to use l2cap_get_chan_by_scid because it looks resposible to
> handle ref_cnt.
>
> Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>
> ---
>  net/bluetooth/l2cap_core.c | 24 +++++++-----------------
>  1 file changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c9de67da..d3a074cbc 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -4291,26 +4291,18 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
>         BT_DBG("dcid 0x%4.4x scid 0x%4.4x result 0x%2.2x status 0x%2.2x",
>                dcid, scid, result, status);
>
> -       mutex_lock(&conn->chan_lock);
> -
>         if (scid) {
> -               chan = __l2cap_get_chan_by_scid(conn, scid);
> -               if (!chan) {
> -                       err = -EBADSLT;
> -                       goto unlock;
> -               }
> +               chan = l2cap_get_chan_by_scid(conn, scid);
> +               if (!chan)
> +                       return -EBADSLT;
>         } else {
> -               chan = __l2cap_get_chan_by_ident(conn, cmd->ident);
> -               if (!chan) {
> -                       err = -EBADSLT;
> -                       goto unlock;
> -               }
> +               chan = l2cap_get_chan_by_ident(conn, cmd->ident);
> +               if (!chan)
> +                       return -EBADSLT;
>         }
>
>         err = 0;
>
> -       l2cap_chan_lock(chan);
> -
>         switch (result) {
>         case L2CAP_CR_SUCCESS:
>                 l2cap_state_change(chan, BT_CONFIG);
> @@ -4336,9 +4328,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
>         }
>
>         l2cap_chan_unlock(chan);
> -
> -unlock:
> -       mutex_unlock(&conn->chan_lock);
> +       l2cap_chan_put(chan);
>
>         return err;
>  }
> --
> 2.25.1

Ive sent a fix yesterday:

https://patchwork.kernel.org/project/bluetooth/patch/20220929203241.4140795-1-luiz.dentz@gmail.com/

Both are sorta similar but the one above end up causing less code
changes which might be easier to backport.

-- 
Luiz Augusto von Dentz