USB: fix use-after-free bug in usb_hcd_unlink_urb()

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@rowland.harvard.edu>
Reported-by: Joe Lawrence <joe.lawrence@stratus.com>
Tested-by: Joe Lawrence <joe.lawrence@stratus.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

1 files changed, 8 insertions, 8 deletions

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 11cee55ae397..45a915ccd71c 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1618,6 +1618,7 @@ 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;
 
@@ -1629,20 +1630,19 @@ 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;
 }