[PATCH] Prevent buffer overflow on USB control endpoint

[Szymon Heidrich <szymon.heidrich@gmail.com>]

Assure that the control endpoint buffer of size USB_BUFSIZ (4096)
can not be overflown during handling of USB control transfer
requests with wLength greater than USB_BUFSIZ.

Signed-off-by: Szymon Heidrich <szymon.heidrich@gmail.com>
---
 drivers/usb/gadget/composite.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 2a309e624e..cb89f6dca9 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1019,6 +1019,17 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 	u8				endp;
 	struct usb_configuration	*c;
 
+	if (w_length > USB_BUFSIZ) {
+		if (ctrl->bRequestType & USB_DIR_IN) {
+			/* Cast away the const, we are going to overwrite on purpose. */
+			__le16 *temp = (__le16 *)&ctrl->wLength;
+			*temp = cpu_to_le16(USB_BUFSIZ);
+			w_length = USB_BUFSIZ;
+		} else {
+			goto done;
+		}
+	}
+
 	/*
 	 * partial re-init of the response message; the function or the
 	 * gadget might need to intercept e.g. a control-OUT completion
-- 
2.38.1