tty: Fix tty_send_xchar() lock order inversion

The correct lock order is atomic_write_lock => termios_rwsem, as
established by tty_write() => n_tty_write().

Fixes: c274f6ef1c666 ("tty: Hold termios_rwsem for tcflow(TCIxxx)")
Reported-and-Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org> # v3.18+
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 0c41dbcb90b8bc7d8ab430d562206e7c2469411f..bcc8e1e8bb720996cf73438c67a397362173edca 100644 (file)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1282,18 +1282,22 @@ int tty_send_xchar(struct tty_struct *tty, char ch)
        int     was_stopped = tty->stopped;
 
        if (tty->ops->send_xchar) {
+               down_read(&tty->termios_rwsem);
                tty->ops->send_xchar(tty, ch);
+               up_read(&tty->termios_rwsem);
                return 0;
        }
 
        if (tty_write_lock(tty, 0) < 0)
                return -ERESTARTSYS;
 
+       down_read(&tty->termios_rwsem);
        if (was_stopped)
                start_tty(tty);
        tty->ops->write(tty, &ch, 1);
        if (was_stopped)
                stop_tty(tty);
+       up_read(&tty->termios_rwsem);
        tty_write_unlock(tty);
        return 0;
 }

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 9c5aebfe7053cbcae1fd65a95f3312509525e8e6..1445dd39aa6227ab641130ef7344eaba9f113b86 100644 (file)
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1147,16 +1147,12 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
                        spin_unlock_irq(&tty->flow_lock);
                        break;
                case TCIOFF:
-                       down_read(&tty->termios_rwsem);
                        if (STOP_CHAR(tty) != __DISABLED_CHAR)
                                retval = tty_send_xchar(tty, STOP_CHAR(tty));
-                       up_read(&tty->termios_rwsem);
                        break;
                case TCION:
-                       down_read(&tty->termios_rwsem);
                        if (START_CHAR(tty) != __DISABLED_CHAR)
                                retval = tty_send_xchar(tty, START_CHAR(tty));
-                       up_read(&tty->termios_rwsem);
                        break;
                default:
                        return -EINVAL;