[PATCH] tty: lock ticogwinsz

Now we lock the set ioctl its trivial to lock the get one so the data
copied is consistent.  At the moment we have the BKL here but this removes
the need for it and is a step in the right direction
Signed-off-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/char/tty_io.c

@@ -2740,18 +2740,21 @@ static int tiocsti(struct tty_struct *tty, char __user *p)
  *	@tty; tty
  *	@arg: user buffer for result
  *
- *	Copies the kernel idea of the window size into the user buffer. No
- *	locking is done.
+ *	Copies the kernel idea of the window size into the user buffer.
  *
- *	FIXME: Returning random values racing a window size set is wrong
- *	should lock here against that
+ *	Locking: tty->termios_sem is taken to ensure the winsize data
+ *		is consistent.
  */
 
 static int tiocgwinsz(struct tty_struct *tty, struct winsize __user * arg)
 {
-	if (copy_to_user(arg, &tty->winsize, sizeof(*arg)))
-		return -EFAULT;
-	return 0;
+	int err;
+
+	down(&tty->termios_sem);
+	err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
+	up(&tty->termios_sem);
+
+	return err ? -EFAULT: 0;
 }
 
 /**