[PATCH v2] greybus/usb: handle unspecified lengths in hub_control

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

Fixes the FIXME in hub_control where response length was not handled
correctly.

The previous implementation always added wLength to the expected
response size, even when wLength was zero. The code also copied wLength
bytes from the response buffer without validating the actual payload
size returned by the Greybus operation.

Compute the response size starting from the fixed header and only add
wLength when it is non-zero. When copying data back to the caller, clamp
the copy size to the actual payload length reported by the Greybus core.
This avoids copying more data than what was actually returned by the
Greybus operation.

Tested by building the driver and issuing hub control requests with
varying wLength values (including zero) and verifying correct behavior.

Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>

---

Changes in v2:
- Document behavior when wLength == 0
- Clamp memcpy() size to actual payload length
- Add testing notes
---
 drivers/staging/greybus/usb.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/greybus/usb.c b/drivers/staging/greybus/usb.c
index 475f24f20cd4..f5f5a4863ddc 100644
--- a/drivers/staging/greybus/usb.c
+++ b/drivers/staging/greybus/usb.c
@@ -105,8 +105,10 @@ static int hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue, u16 wIndex,
 	size_t response_size;
 	int ret;
 
-	/* FIXME: handle unspecified lengths */
-	response_size = sizeof(*response) + wLength;
+	/* Calculate expected response size */
+	response_size = sizeof(*response);
+	if (wLength)
+		response_size += wLength;
 
 	operation = gb_operation_create(dev->connection,
 					GB_USB_TYPE_HUB_CONTROL,
@@ -127,9 +129,13 @@ static int hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue, u16 wIndex,
 		goto out;
 
 	if (wLength) {
-		/* Greybus core has verified response size */
-		response = operation->response->payload;
-		memcpy(buf, response->buf, wLength);
+		size_t actual_size = operation->response->payload_size - sizeof(*response);
+		size_t copy_size = min(wLength, actual_size);
+
+		if (copy_size) {
+			response = operation->response->payload;
+			memcpy(buf, response->buf, copy_size);
+		}
 	}
 out:
 	gb_operation_put(operation);
-- 
2.53.0