linux-kernel - [PATCH 3.16.y-ckt 065/183] USB: fix use-after-free bug in usb_hcd_unlink

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Message-Id: <1425635874-19087-66-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  6 Mar 2015 09:55:56 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 065/183] USB: fix use-after-free bug in usb_hcd_unlink_urb()

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@...land.harvard.edu>

commit c99197902da284b4b723451c1471c45b18537cde upstream.

The usb_hcd_unlink_urb() routine in hcd.c contains two possible
use-after-free errors.  The dev_dbg() statement at the end of the
routine dereferences urb and urb->dev even though both structures may
have been deallocated.

This patch fixes the problem by storing urb->dev in a local variable
(avoiding the dereference of urb) and moving the dev_dbg() up before
the usb_put_dev() call.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Reported-by: Joe Lawrence <joe.lawrence@...atus.com>
Tested-by: Joe Lawrence <joe.lawrence@...atus.com>
Signed-off-by: Greg Kroah-Hartman <greg@...ah.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/usb/core/hcd.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 23d44ac95cd6..4195906f94d6 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1621,6 +1621,7 @@ static int unlink1(struct usb_hcd *hcd, struct urb *urb, int status)
 int usb_hcd_unlink_urb (struct urb *urb, int status)
 {
 	struct usb_hcd		*hcd;
+	struct usb_device	*udev = urb->dev;
 	int			retval = -EIDRM;
 	unsigned long		flags;
 
@@ -1632,20 +1633,19 @@ int usb_hcd_unlink_urb (struct urb *urb, int status)
 	spin_lock_irqsave(&hcd_urb_unlink_lock, flags);
 	if (atomic_read(&urb->use_count) > 0) {
 		retval = 0;
-		usb_get_dev(urb->dev);
+		usb_get_dev(udev);
 	}
 	spin_unlock_irqrestore(&hcd_urb_unlink_lock, flags);
 	if (retval == 0) {
 		hcd = bus_to_hcd(urb->dev->bus);
 		retval = unlink1(hcd, urb, status);
-		usb_put_dev(urb->dev);
+		if (retval == 0)
+			retval = -EINPROGRESS;
+		else if (retval != -EIDRM && retval != -EBUSY)
+			dev_dbg(&udev->dev, "hcd_unlink_urb %p fail %d\n",
+					urb, retval);
+		usb_put_dev(udev);
 	}
-
-	if (retval == 0)
-		retval = -EINPROGRESS;
-	else if (retval != -EIDRM && retval != -EBUSY)
-		dev_dbg(&urb->dev->dev, "hcd_unlink_urb %p fail %d\n",
-				urb, retval);
 	return retval;
 }
 
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