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    Subject[PATCH v2] Bluetooth: Fix possible deadlock in rfcomm_sk_state_change
    Date
    There's a possible deadlock when two processes are connecting
    and closing a RFCOMM socket concurrently. 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@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;
    }

    --
    2.39.0.314.g84b9a713c41-goog
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