tty: Hold termios_rwsem for tcflow(TCIxxx)

While transmitting a START/STOP char for tcflow(TCION/TCIOFF), prevent
a termios change. Otherwise, a garbage in-band flow control char
may be sent, if the termios change overlaps the transmission setup.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index ad9120d1c0f1b247b19c4e6d22d191883f736dc7..62380ccf70fb469f3e3c676452819ecfdf6ff4b5 100644 (file)
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1164,17 +1164,21 @@ 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)
-                               return tty_send_xchar(tty, STOP_CHAR(tty));
+                               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)
-                               return tty_send_xchar(tty, START_CHAR(tty));
+                               retval = tty_send_xchar(tty, START_CHAR(tty));
+                       up_read(&tty->termios_rwsem);
                        break;
                default:
                        return -EINVAL;
                }
-               return 0;
+               return retval;
        case TCFLSH:
                retval = tty_check_change(tty);
                if (retval)