KASAN found a use-after-free in xhci_free_virt_device+0x33b/0x38e
where xhci_free_virt_device() sets slot id to 0 if udev exists:
if (dev->udev && dev->udev->slot_id)
        dev->udev->slot_id = 0;

dev->udev will be true even if udev is freed because dev->udev is
not set to NULL.

set dev->udev pointer to NULL in xhci_free_dev()

The original patch went to stable so this fix needs to be applied
there as well.

Fixes: a400efe455f7 ("xhci: zero usb device slot_id member when disabling and 
freeing a xhci slot")
Cc: <sta...@vger.kernel.org>
Reported-by: Guenter Roeck <li...@roeck-us.net>
Reviewed-by: Guenter Roeck <li...@roeck-us.net>
Tested-by: Guenter Roeck <li...@roeck-us.net>
Signed-off-by: Mathias Nyman <mathias.ny...@linux.intel.com>
---
 drivers/usb/host/xhci.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 9b27798..711da33 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -3621,6 +3621,7 @@ static void xhci_free_dev(struct usb_hcd *hcd, struct 
usb_device *udev)
                del_timer_sync(&virt_dev->eps[i].stop_cmd_timer);
        }
        xhci_debugfs_remove_slot(xhci, udev->slot_id);
+       virt_dev->udev = NULL;
        ret = xhci_disable_slot(xhci, udev->slot_id);
        if (ret)
                xhci_free_virt_device(xhci, udev->slot_id);
-- 
2.7.4

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