xhci: check virt_dev is valid before dereferencing it

Check that the xhci_virt_dev structure that we dug out based
on a slot_id value from a command completion is valid before
dereferencing it.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210129130044.206855-7-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-ring.c

@@ -1273,6 +1273,8 @@ static void xhci_handle_cmd_config_ep(struct xhci_hcd *xhci, int slot_id,
 	 * is not waiting on the configure endpoint command.
 	 */
 	virt_dev = xhci->devs[slot_id];
+	if (!virt_dev)
+		return;
 	ctrl_ctx = xhci_get_input_control_ctx(virt_dev->in_ctx);
 	if (!ctrl_ctx) {
 		xhci_warn(xhci, "Could not get input context, bad type.\n");
@@ -1317,6 +1319,8 @@ static void xhci_handle_cmd_addr_dev(struct xhci_hcd *xhci, int slot_id)
 	struct xhci_slot_ctx *slot_ctx;
 
 	vdev = xhci->devs[slot_id];
+	if (!vdev)
+		return;
 	slot_ctx = xhci_get_slot_ctx(xhci, vdev->out_ctx);
 	trace_xhci_handle_cmd_addr_dev(slot_ctx);
 }
@@ -1327,13 +1331,15 @@ static void xhci_handle_cmd_reset_dev(struct xhci_hcd *xhci, int slot_id)
 	struct xhci_slot_ctx *slot_ctx;
 
 	vdev = xhci->devs[slot_id];
+	if (!vdev) {
+		xhci_warn(xhci, "Reset device command completion for disabled slot %u\n",
+			  slot_id);
+		return;
+	}
 	slot_ctx = xhci_get_slot_ctx(xhci, vdev->out_ctx);
 	trace_xhci_handle_cmd_reset_dev(slot_ctx);
 
 	xhci_dbg(xhci, "Completed reset device command.\n");
-	if (!xhci->devs[slot_id])
-		xhci_warn(xhci, "Reset device command completion "
-				"for disabled slot %u\n", slot_id);
 }
 
 static void xhci_handle_cmd_nec_get_fw(struct xhci_hcd *xhci,