[PATCH] usb: host: add cast to avoid potential integer overflow

[PATCH] usb: host: add cast to avoid potential integer overflow

[Gustavo A. R. Silva]

The type of variable 'sel' is unsigned int. Such variable is being used
multiple times in a context that expects an expression of type unsigned
long long. So, to avoid any potential integer overflow, a cast to type
unsigned long long is added.

Addresses-Coverity-ID: 703408
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
---
 drivers/usb/host/xhci.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 50aee8b..8094d9a 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -4298,23 +4298,23 @@ static unsigned long long xhci_calculate_intel_u1_timeout(
 	ep_type = usb_endpoint_type(desc);
 	switch (ep_type) {
 	case USB_ENDPOINT_XFER_CONTROL:
-		timeout_ns = udev->u1_params.sel * 3;
+		timeout_ns = (unsigned long long)udev->u1_params.sel * 3;
 		break;
 	case USB_ENDPOINT_XFER_BULK:
-		timeout_ns = udev->u1_params.sel * 5;
+		timeout_ns = (unsigned long long)udev->u1_params.sel * 5;
 		break;
 	case USB_ENDPOINT_XFER_INT:
 		intr_type = usb_endpoint_interrupt_type(desc);
 		if (intr_type == USB_ENDPOINT_INTR_NOTIFICATION) {
-			timeout_ns = udev->u1_params.sel * 3;
+			timeout_ns = (unsigned long long)udev->u1_params.sel * 3;
 			break;
 		}
 		/* Otherwise the calculation is the same as isoc eps */
 	case USB_ENDPOINT_XFER_ISOC:
 		timeout_ns = xhci_service_interval_to_ns(desc);
 		timeout_ns = DIV_ROUND_UP_ULL(timeout_ns * 105, 100);
-		if (timeout_ns < udev->u1_params.sel * 2)
-			timeout_ns = udev->u1_params.sel * 2;
+		if (timeout_ns < (unsigned long long)udev->u1_params.sel * 2)
+			timeout_ns = (unsigned long long)udev->u1_params.sel * 2;
 		break;
 	default:
 		return 0;
-- 
2.5.0

RE: [PATCH] usb: host: add cast to avoid potential integer overflow

[David Laight]

From: Gustavo A. R. Silva
> Sent: 17 February 2017 00:17
> The type of variable 'sel' is unsigned int. Such variable is being used
> multiple times in a context that expects an expression of type unsigned
> long long. So, to avoid any potential integer overflow, a cast to type
> unsigned long long is added.
...
> -		timeout_ns = udev->u1_params.sel * 3;
> +		timeout_ns = (unsigned long long)udev->u1_params.sel * 3;
...

It is probably better to just change the constant to 3ull.
However I'd be tempted to look more closely at the valid values
for 'timeout_ns'.
It seems unlikely that that the timeout (in sel) will be near
enough to 4 seconds that multiplying by a small integer will
take the value over 4 seconds without requiring larger input
values be supported.

timeout_ns might even be being used in places where the value
has to be smaller than 1 second!

	David