[PATCH 1/2] vt: stabilize tty reference in kbd_keycode with tty_port_tty_get

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Joshua Rogers <linux@joshua.hu>

kbd_keycode() reads vc->port.tty without acquiring a tty reference,
racing against con_shutdown() which clears port.tty under a different
lock. Use tty_port_tty_get()/tty_kref_put() to hold a proper reference
for the duration the tty pointer is needed.

Assisted-by: AISLE:Snapshot
Signed-off-by: Joshua Rogers <linux@joshua.hu>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/vt/keyboard.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 763a3f1b7be0..c41d850b29c6 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1437,7 +1437,7 @@ static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
 	struct keyboard_notifier_param param = { .vc = vc, .value = keycode, .down = down };
 	int rc;
 
-	tty = vc->port.tty;
+	tty = tty_port_tty_get(&vc->port);
 
 	if (tty && (!tty->driver_data)) {
 		/* No driver data? Strange. Okay we fix it then. */
@@ -1497,9 +1497,12 @@ static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
 		 * characters get aren't echoed locally. This makes key repeat
 		 * usable with slow applications and under heavy loads.
 		 */
+		tty_kref_put(tty);
 		return;
 	}
 
+	tty_kref_put(tty);
+
 	param.shift = shift_final = (shift_state | kbd->slockstate) ^ kbd->lockstate;
 	param.ledstate = kbd->ledflagstate;
 	key_map = key_maps[shift_final];

-- 
2.55.0