USB: console: fix potential use after free

commit 32a4bf2e81ec378e5925d4e069e0677a6c86a6ad upstream.

Use tty kref to release the fake tty in usb_console_setup to avoid use
after free if the underlying serial driver has acquired a reference.

Note that using the tty destructor release_one_tty requires some more
state to be initialised.

Fixes: 4a90f09b20f4 ("tty: usb-serial krefs")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/serial/console.c b/drivers/usb/serial/console.c
index 1ee6b2a..87302dd 100644 (file)
--- a/drivers/usb/serial/console.c
+++ b/drivers/usb/serial/console.c
@@ -47,6 +47,8 @@ static struct console usbcons;
  * ------------------------------------------------------------
  */
 
+static const struct tty_operations usb_console_fake_tty_ops = {
+};
 
 /*
  * The parsing of the command line works exactly like the
@@ -141,14 +143,17 @@ static int usb_console_setup(struct console *co, char *options)
                                goto reset_open_count;
                        }
                        kref_init(&tty->kref);
-                       tty_port_tty_set(&port->port, tty);
                        tty->driver = usb_serial_tty_driver;
                        tty->index = co->index;
+                       INIT_LIST_HEAD(&tty->tty_files);
+                       kref_get(&tty->driver->kref);
+                       tty->ops = &usb_console_fake_tty_ops;
                        if (tty_init_termios(tty)) {
                                retval = -ENOMEM;
                                err("no more memory");
-                               goto free_tty;
+                               goto put_tty;
                        }
+                       tty_port_tty_set(&port->port, tty);
                }
 
                /* only call the device specific open if this
@@ -170,7 +175,7 @@ static int usb_console_setup(struct console *co, char *options)
                        serial->type->set_termios(tty, port, &dummy);
 
                        tty_port_tty_set(&port->port, NULL);
-                       kfree(tty);
+                       tty_kref_put(tty);
                }
                set_bit(ASYNCB_INITIALIZED, &port->port.flags);
        }
@@ -186,8 +191,8 @@ static int usb_console_setup(struct console *co, char *options)
 
  fail:
        tty_port_tty_set(&port->port, NULL);
- free_tty:
-       kfree(tty);
+ put_tty:
+       tty_kref_put(tty);
  reset_open_count:
        port->port.count = 0;
        usb_autopm_put_interface(serial->interface);