USB: console: fix potential use after free

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")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/drivers/usb/serial/console.c b/drivers/usb/serial/console.c
index e56f394b58d8..29fa1c3d0089 100644
--- a/drivers/usb/serial/console.c
+++ b/drivers/usb/serial/console.c
@@ -46,6 +46,8 @@ static struct console usbcons;
  * ------------------------------------------------------------
  */
 
+static const struct tty_operations usb_console_fake_tty_ops = {
+};
 
 /*
  * The parsing of the command line works exactly like the
@@ -137,14 +139,17 @@ 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_ldsem(&tty->ldisc_sem);
+                        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;
-                                goto free_tty;
+                                goto put_tty;
                         }
+                        tty_port_tty_set(&port->port, tty);
                 }
 
                 /* only call the device specific open if this
@@ -162,7 +167,7 @@ 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);
         }
@@ -178,8 +183,8 @@ 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);