[SRU] [jammy:linux-xilinx-zynqmp 14/14] serial: fix TIOCSRS485 locking

[Portia Stephens]

From: Johan Hovold <johan at kernel.org>

BugLink: https://bugs.launchpad.net/bugs/2055237

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 at vger.kernel.org	# 6.0
Cc: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>
Signed-off-by: Johan Hovold <johan at kernel.org>
Link: https://lore.kernel.org/r/20230412124811.11217-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from 9e4f2a8004213339e9d837d891a59cc80e082966)
Signed-off-by: Portia Stephens <portia.stephens at canonical.com>
---
 drivers/tty/serial/serial_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 2170721186f6b..d90184953977c 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1445,7 +1445,7 @@ 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);
@@ -1488,7 +1488,7 @@ 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;
-- 
2.34.1