[PATCH] USB Serial: fix use-after-free bug in usb-serial core

This fixes a use-after-free bug in the usb-serial core.  It is simple to
trigger this (open a usb-serial port, then yank the device out before
closing the port.)  Thanks to Stefan Seyfried <seife@suse.de> for
reporting this, and to the slab debugging code which enabled it to be
tracked down.

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/usb/serial/usb-serial.c

@@ -242,8 +242,10 @@ static void serial_close(struct tty_struct *tty, struct file * filp)
 
 	down(&port->sem);
 
-	if (port->open_count == 0)
-		goto out;
+	if (port->open_count == 0) {
+		up(&port->sem);
+		return;
+	}
 
 	--port->open_count;
 	if (port->open_count == 0) {
@@ -260,10 +262,8 @@ static void serial_close(struct tty_struct *tty, struct file * filp)
 		module_put(port->serial->type->driver.owner);
 	}
 
-	kref_put(&port->serial->kref, destroy_serial);
-
-out:
 	up(&port->sem);
+	kref_put(&port->serial->kref, destroy_serial);
 }
 
 static int serial_write (struct tty_struct * tty, const unsigned char *buf, int count)