linux-kernel - [PATCH] usb: usbfs: fix crash in check_ctrlrecip()->usb_find_alt

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Date:   Tue, 25 Sep 2018 14:22:42 +0200
From:   Vladis Dronov <vdronov@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Oliver Neukum <oneukum@...e.com>,
        Hans de Goede <hdegoede@...hat.com>,
        syzkaller@...glegroups.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     stable <stable@...r.kernel.org>, Vladis Dronov <vdronov@...hat.com>
Subject: [PATCH] usb: usbfs: fix crash in check_ctrlrecip()->usb_find_alt_setting()

ps->dev->actconfig can be NULL and cause NULL-deref in usb_find_alt_setting()
before c9a4cb204e9e. fix this anyway by checking that ps->dev->actconfig is not
NULL, so usb_find_alt_setting() is not called with a known-bad argument.

Signed-off-by: Vladis Dronov <vdronov@...hat.com>
Reported-by: syzbot+19c3aaef85a89d451eac@...kaller.appspotmail.com
---
 drivers/usb/core/devio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 6ce77b33da61..26047620b003 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -824,7 +824,7 @@ static int check_ctrlrecip(struct usb_dev_state *ps, unsigned int requesttype,
 	 * class specification, which we always want to allow as it is used
 	 * to query things like ink level, etc.
 	 */
-	if (requesttype == 0xa1 && request == 0) {
+	if (requesttype == 0xa1 && request == 0 && ps->dev->actconfig) {
 		alt_setting = usb_find_alt_setting(ps->dev->actconfig,
 						   index >> 8, index & 0xff);
 		if (alt_setting
-- 
2.14.4