[3.16.y-ckt stable] Patch "USB: console: fix potential use after free" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    USB: console: fix potential use after free

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2b78e4b755d00313babb1dbe34ece4183cf090f2 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan at kernel.org>
Date: Mon, 5 Jan 2015 16:04:13 +0100
Subject: 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 at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/serial/console.c | 15 ++++++++++-----
 1 file 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);
--
2.1.4