[PATCH 5.4 055/102] tty: fix compat TIOCGSERIAL checking wrong function ptr

[Greg Kroah-Hartman]

From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit 6e622cd8bd888c7fa3ee2b7dfb3514ab53b21570 upstream.

Commit 77654350306a ("take compat TIOC[SG]SERIAL treatment into
tty_compat_ioctl()") changed the compat version of TIOCGSERIAL to start
checking for the presence of the ->set_serial function pointer rather
than ->get_serial.  This appears to be a copy-and-paste error, since
->get_serial is the function pointer that is called as well as the
pointer that is checked by the non-compat version of TIOCGSERIAL.

Fix this by checking the correct function pointer.

Fixes: 77654350306a ("take compat TIOC[SG]SERIAL treatment into tty_compat_ioctl()")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.20+
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Acked-by: Jiri Slaby <jslaby@xxxxxxx>
Link: https://lore.kernel.org/r/20200224182044.234553-3-ebiggers@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/tty_io.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2735,7 +2735,7 @@ static int compat_tty_tiocgserial(struct
 	memset(&v, 0, sizeof(v));
 	memset(&v32, 0, sizeof(v32));
 
-	if (!tty->ops->set_serial)
+	if (!tty->ops->get_serial)
 		return -ENOTTY;
 	err = tty->ops->get_serial(tty, &v);
 	if (!err) {