xhci: don't create endpoint debugfs entry before ring buffer is set.

[ Upstream commit 167657a ]

Make sure xHC completes the configure endpoint command and xhci driver
sets the ring pointers correctly before we create the user readable
debugfs file.

In theory there was a small gap where a user could have read the
debugfs file and cause a NULL pointer dereference error as ring
pointer was not yet set, in practise we want this change to simplify
the upcoming streams debugfs support.

Fixes: 02b6fdc ("usb: xhci: Add debugfs interface for xHCI driver")
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200918131752.16488-10-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/usb/host/xhci.c

@@ -1915,8 +1915,6 @@ static int xhci_add_endpoint(struct usb_hcd *hcd, struct usb_device *udev,
 	ep_ctx = xhci_get_ep_ctx(xhci, virt_dev->in_ctx, ep_index);
 	trace_xhci_add_endpoint(ep_ctx);
 
-	xhci_debugfs_create_endpoint(xhci, virt_dev, ep_index);
-
 	xhci_dbg(xhci, "add ep 0x%x, slot id %d, new drop flags = %#x, new add flags = %#x\n",
 			(unsigned int) ep->desc.bEndpointAddress,
 			udev->slot_id,
@@ -2949,6 +2947,7 @@ static int xhci_check_bandwidth(struct usb_hcd *hcd, struct usb_device *udev)
 		xhci_check_bw_drop_ep_streams(xhci, virt_dev, i);
 		virt_dev->eps[i].ring = virt_dev->eps[i].new_ring;
 		virt_dev->eps[i].new_ring = NULL;
+		xhci_debugfs_create_endpoint(xhci, virt_dev, i);
 	}
 command_cleanup:
 	kfree(command->completion);