Messages in this thread | | | Date | Thu, 5 Jan 2023 17:18:33 -0800 | From | Saeed Mahameed <> | Subject | Re: [PATCH v2] Bluetooth: Fix possible deadlock in rfcomm_sk_state_change |
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On 04 Jan 14:21, Luiz Augusto von Dentz wrote: >Hi Ying, > >On Wed, Jan 4, 2023 at 7:07 AM Ying Hsu <yinghsu@chromium.org> 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@chromium.org> >> --- >> 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
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