[PATCH 5.10.y] tty: tty_port: restore TTY_IO_ERROR on activation failure

[Sasha Levin <sashal@kernel.org>]

From: Johan Hovold <johan@kernel.org>

[ Upstream commit 56964f6a31238fb41d5830bb42520c5b10ff7d8f ]

Make sure to restore the TTY_IO_ERROR flag if activation fails to
prevent I/O attempts on a port that is gone or powered down.

This specifically avoids issues like kernel panic due to unclocked
accesses or NULL-pointer dereferences when accessing powered down or
deregistered ports when a TTY ioctl races with hangup and open.

Note that the flag is set again in tty_port_close() but not restoring it
on activation failure leaves a window where drivers fail to handle the
ioctl-hangup race.

Fixes: a9a37ec33a1b ("tty: tty_port: Move the IO_ERROR clear")
Cc: stable <stable@kernel.org>  # 2.6.33
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260908084000.218528-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ sashal: adapted to the existing braced error block containing mutex_unlock() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/tty_port.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index cbb56f725bc4a..77e28059ad982 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -689,6 +689,7 @@ int tty_port_open(struct tty_port *port, struct tty_struct *tty,
 		if (port->ops->activate) {
 			int retval = port->ops->activate(port, tty);
 			if (retval) {
+				set_bit(TTY_IO_ERROR, &tty->flags);
 				mutex_unlock(&port->mutex);
 				return retval;
 			}
-- 
2.53.0