xhci: check slot_id is valid before gathering slot info

Check that the slot_id that we dug out from command completion event
TRB, is valid before using it to identify the slot associated with the
command that generated the event.
Signed-off-by: NLalithambika Krishna Kumar <lalithambika.krishnakumar@intel.com>
Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210129130044.206855-11-mathias.nyman@linux.intel.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-ring.c

@@ -1430,7 +1430,7 @@ void xhci_handle_command_timeout(struct work_struct *work)
 static void handle_cmd_completion(struct xhci_hcd *xhci,
 		struct xhci_event_cmd *event)
 {
-	int slot_id = TRB_TO_SLOT_ID(le32_to_cpu(event->flags));
+	unsigned int slot_id = TRB_TO_SLOT_ID(le32_to_cpu(event->flags));
 	u64 cmd_dma;
 	dma_addr_t cmd_dequeue_dma;
 	u32 cmd_comp_code;
@@ -1438,6 +1438,11 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 	struct xhci_command *cmd;
 	u32 cmd_type;
 
+	if (slot_id >= MAX_HC_SLOTS) {
+		xhci_warn(xhci, "Invalid slot_id %u\n", slot_id);
+		return;
+	}
+
 	cmd_dma = le64_to_cpu(event->cmd_trb);
 	cmd_trb = xhci->cmd_ring->dequeue;