[PATCH 5.11 014/601] staging: fwserial: fix TIOCSSERIAL permission check

[Greg Kroah-Hartman]

From: Johan Hovold <johan@xxxxxxxxxx>

commit 2104eb283df66a482b60254299acbe3c68c03412 upstream.

Changing the port close-delay parameter is a privileged operation so
make sure to return -EPERM if a regular user tries to change it.

Fixes: 7355ba3445f2 ("staging: fwserial: Add TTY-over-Firewire serial driver")
Cc: stable@xxxxxxxxxxxxxxx      # 3.8
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210407102334.32361-3-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/staging/fwserial/fwserial.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/staging/fwserial/fwserial.c
+++ b/drivers/staging/fwserial/fwserial.c
@@ -1232,20 +1232,24 @@ static int set_serial_info(struct tty_st
 			   struct serial_struct *ss)
 {
 	struct fwtty_port *port = tty->driver_data;
+	unsigned int cdelay;
 
 	if (ss->irq != 0 || ss->port != 0 || ss->custom_divisor != 0 ||
 	    ss->baud_base != 400000000)
 		return -EPERM;
 
+	cdelay = msecs_to_jiffies(ss->close_delay * 10);
+
 	mutex_lock(&port->port.mutex);
 	if (!capable(CAP_SYS_ADMIN)) {
-		if (((ss->flags & ~ASYNC_USR_MASK) !=
+		if (cdelay != port->port.close_delay ||
+		    ((ss->flags & ~ASYNC_USR_MASK) !=
 		     (port->port.flags & ~ASYNC_USR_MASK))) {
 			mutex_unlock(&port->port.mutex);
 			return -EPERM;
 		}
 	}
-	port->port.close_delay = msecs_to_jiffies(ss->close_delay * 10);
+	port->port.close_delay = cdelay;
 	mutex_unlock(&port->port.mutex);
 
 	return 0;