serial: fix TIOCSRS485 locking

commit 9e4f2a8004213339e9d837d891a59cc80e082966 upstream.

The RS485 multipoint addressing support for some reason added a new
ADDRB termios cflag which is (only!) updated from one of the RS485
ioctls.

Make sure to take the termios rw semaphore for the right ioctl (i.e.
set, not get).

Fixes: ae50bb275283 ("serial: take termios_rwsem for ->rs485_config() & pass termios as param")
Cc: stable@vger.kernel.org	# 6.0
Cc: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20230412124811.11217-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index ec874f3a567ca79bea6fd1d3503f5b78dfba4f8b..eea526d34fdda48cd877ff8aafb3426febfcb845 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1552,7 +1552,7 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
                goto out;
 
        /* rs485_config requires more locking than others */
-       if (cmd == TIOCGRS485)
+       if (cmd == TIOCSRS485)
                down_write(&tty->termios_rwsem);
 
        mutex_lock(&port->mutex);
@@ -1595,7 +1595,7 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
        }
 out_up:
        mutex_unlock(&port->mutex);
-       if (cmd == TIOCGRS485)
+       if (cmd == TIOCSRS485)
                up_write(&tty->termios_rwsem);
 out:
        return ret;