[CVE-2017-16525][SRU][Trusty][Zesty][PATCH 2/2] USB: serial: console: fix use-after-free on disconnect

[Po-Hsu Lin]

From: Johan Hovold <johan at kernel.org>

CVE-2017-16525

A clean-up patch removing two redundant NULL-checks from the console
disconnect handler inadvertently also removed a third check. This could
lead to the struct usb_serial being prematurely freed by the console
code when a driver accepts but does not register any ports for an
interface which also lacks endpoint descriptors.

Fixes: 0e517c93dc02 ("USB: serial: console: clean up sanity checks")
Cc: stable <stable at vger.kernel.org>     # 4.11
Reported-by: Andrey Konovalov <andreyknvl at google.com>
Acked-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Johan Hovold <johan at kernel.org>
(backported from commit bd998c2e0df0469707503023d50d46cf0b10c787)
Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
---
 drivers/usb/serial/console.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/usb/serial/console.c b/drivers/usb/serial/console.c
index 76062ce..43a862a 100644
--- a/drivers/usb/serial/console.c
+++ b/drivers/usb/serial/console.c
@@ -266,8 +266,7 @@ static struct console usbcons = {
 
 void usb_serial_console_disconnect(struct usb_serial *serial)
 {
-	if (serial && serial->port && serial->port[0]
-				&& serial->port[0] == usbcons_info.port) {
+	if (serial->port[0] && serial->port[0] == usbcons_info.port) {
 		usb_serial_console_exit();
 		usb_serial_put(serial);
 	}
-- 
2.7.4