[PATCH 3.2 102/152] USB: console: fix potential use after free

Ben Hutchings
2015-02-17T01:46:53Z

From: Johan Hovold <johan@kernel.org>

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>
---
drivers/usb/serial/console.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

--- 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 cons
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 cons
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 cons

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);