On 04 Jan 14:21, Luiz Augusto von Dentz wrote:
Hi Ying,
On Wed, Jan 4, 2023 at 7:07 AM Ying Hsu <yinghsu@xxxxxxxxxxxx> wrote:
There's a possible deadlock when two processes are connecting
and closing a RFCOMM socket concurrently. Here's the call trace:
Are you sure it is 2 different processes? Usually that would mean 2
different sockets (sk) then so they wouldn't share the same lock, so
this sounds more like 2 different threads, perhaps it is worth
creating a testing case in our rfcomm-tester so we are able to detect
this sort of thing in the future.
-> #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
and a ChromeOS device.
Changes in v2:
- Fix potential use-after-free in rfc_comm_sock_connect.
net/bluetooth/rfcomm/sock.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index 21e24da4847f..4397e14ff560 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -391,6 +391,7 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a
addr->sa_family != AF_BLUETOOTH)
return -EINVAL;
+ sock_hold(sk);
lock_sock(sk);
if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
@@ -410,14 +411,18 @@ 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;
+ /* Drop sock lock to avoid potential deadlock with the RFCOMM lock */
+ release_sock(sk);
err = rfcomm_dlc_open(d, &rfcomm_pi(sk)->src, &sa->rc_bdaddr,
sa->rc_channel);
- if (!err)
+ lock_sock(sk);
+ if (!err && !sock_flag(sk, SOCK_ZAPPED))
err = bt_sock_wait_state(sk, BT_CONNECTED,
sock_sndtimeo(sk, flags & O_NONBLOCK));
done:
release_sock(sk);
+ sock_put(sk);
return err;
}
This sounds like a great solution to hold the reference and then
Why do you need sock_hold/put in the same proto_ops.callback sock opts ?
it should be guaranteed by the caller the sk will remain valid
or if you are paranoid then sock_hold() on your proto_ops.bind() and put()
on your proto_ops.release()
checking if the socket has been zapped when attempting to lock_sock,
so Ive been thinking on generalize this into something like
bt_sock_connect(sock, addr, alen, callback) so we make sure the
callback is done while holding a reference but with the socket
unlocked since typically the underline procedure only needs to access
the pi(sk) information without changing it e.g. rfcomm_dlc_open,
anyway Im fine if you don't want to pursue doing it right now but I'm
afraid these type of locking problem is no restricted to RFCOMM only.
--
2.39.0.314.g84b9a713c41-goog
--
Luiz Augusto von Dentz
