[PATCH] Bluetooth: Fix possible deadlock in rfcomm_sk_state_change

[Ying Hsu]

There's a possible deadlock when two processes are connecting
and closing concurrently:
  + CPU0: __rfcomm_dlc_close locks rfcomm and then calls
  rfcomm_sk_state_change which locks the sock.
  + CPU1: rfcomm_sock_connect locks the socket and then calls
  rfcomm_dlc_open which locks rfcomm.

Here's the call trace:

-> #2 (&d->lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock0x12f/0x1360 kernel/locking/mutex.c:747
       __rfcomm_dlc_close+0x15d/0x890 net/bluetooth/rfcomm/core.c:487
       rfcomm_dlc_close+1e9/0x240 net/bluetooth/rfcomm/core.c:520
       __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220
       rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907
       rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928
       __sock_release+0xcd/0x280 net/socket.c:650
       sock_close+0x1c/0x20 net/socket.c:1365
       __fput+0x27c/0xa90 fs/file_table.c:320
       task_work_run+0x16f/0x270 kernel/task_work.c:179
       exit_task_work include/linux/task_work.h:38 [inline]
       do_exit+0xaa8/0x2950 kernel/exit.c:867
       do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
       get_signal+0x21c3/0x2450 kernel/signal.c:2859
       arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
       exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
       exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
       __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
       syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
       do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #1 (rfcomm_mutex){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12f/0x1360 kernel/locking/mutex.c:747
       rfcomm_dlc_open+0x93/0xa80 net/bluetooth/rfcomm/core.c:425
       rfcomm_sock_connect+0x329/0x450 net/bluetooth/rfcomm/sock.c:413
       __sys_connect_file+0x153/0x1a0 net/socket.c:1976
       __sys_connect+0x165/0x1a0 net/socket.c:1993
       __do_sys_connect net/socket.c:2003 [inline]
       __se_sys_connect net/socket.c:2000 [inline]
       __x64_sys_connect+0x73/0xb0 net/socket.c:2000
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3097 [inline]
       check_prevs_add kernel/locking/lockdep.c:3216 [inline]
       validate_chain kernel/locking/lockdep.c:3831 [inline]
       __lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055
       lock_acquire kernel/locking/lockdep.c:5668 [inline]
       lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
       lock_sock_nested+0x3a/0xf0 net/core/sock.c:3470
       lock_sock include/net/sock.h:1725 [inline]
       rfcomm_sk_state_change+0x6d/0x3a0 net/bluetooth/rfcomm/sock.c:73
       __rfcomm_dlc_close+0x1b1/0x890 net/bluetooth/rfcomm/core.c:489
       rfcomm_dlc_close+0x1e9/0x240 net/bluetooth/rfcomm/core.c:520
       __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220
       rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907
       rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928
       __sock_release+0xcd/0x280 net/socket.c:650
       sock_close+0x1c/0x20 net/socket.c:1365
       __fput+0x27c/0xa90 fs/file_table.c:320
       task_work_run+0x16f/0x270 kernel/task_work.c:179
       exit_task_work include/linux/task_work.h:38 [inline]
       do_exit+0xaa8/0x2950 kernel/exit.c:867
       do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
       get_signal+0x21c3/0x2450 kernel/signal.c:2859
       arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
       exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
       exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
       __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
       syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
       do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

Signed-off-by: Ying Hsu <yinghsu@xxxxxxxxxxxx>
---
This commit has been tested with a C reproducer on qemu-x86_64.

 net/bluetooth/rfcomm/sock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index 21e24da4847f..29f9a88a3dc8 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -410,8 +410,10 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a
 	d->sec_level = rfcomm_pi(sk)->sec_level;
 	d->role_switch = rfcomm_pi(sk)->role_switch;
 
+	release_sock(sk);
 	err = rfcomm_dlc_open(d, &rfcomm_pi(sk)->src, &sa->rc_bdaddr,
 			      sa->rc_channel);
+	lock_sock(sk);
 	if (!err)
 		err = bt_sock_wait_state(sk, BT_CONNECTED,
 				sock_sndtimeo(sk, flags & O_NONBLOCK));
-- 
2.39.0.314.g84b9a713c41-goog