[PATCH v4 03/10] usb: gadget: align buffer size when allocating for OUT endpoint

["Felipe F. Tonello" <eu@felipetonello.com>]

Using usb_ep_align() makes sure that the buffer size for OUT endpoints is
always aligned with wMaxPacketSize (512 usually). This makes sure
that no buffer has the wrong size, which can cause nasty bugs.

Signed-off-by: Felipe F. Tonello <eu@felipetonello.com>
---
 drivers/usb/gadget/u_f.c |  3 +++
 drivers/usb/gadget/u_f.h | 16 +++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/u_f.c b/drivers/usb/gadget/u_f.c
index 6811761fec64..907f8144813c 100644
--- a/drivers/usb/gadget/u_f.c
+++ b/drivers/usb/gadget/u_f.c
@@ -12,6 +12,7 @@
  */
 
 #include "u_f.h"
+#include <linux/usb/ch9.h>
 
 struct usb_request *alloc_ep_req(struct usb_ep *ep, size_t len, int default_len)
 {
@@ -20,6 +21,8 @@ struct usb_request *alloc_ep_req(struct usb_ep *ep, size_t len, int default_len)
 	req = usb_ep_alloc_request(ep, GFP_ATOMIC);
 	if (req) {
 		req->length = len ?: default_len;
+		if (usb_endpoint_dir_out(ep->desc))
+			req->length = usb_ep_align(ep, req->length);
 		req->buf = kmalloc(req->length, GFP_ATOMIC);
 		if (!req->buf) {
 			usb_ep_free_request(ep, req);
diff --git a/drivers/usb/gadget/u_f.h b/drivers/usb/gadget/u_f.h
index 21b75710c4a4..69a1d10df04f 100644
--- a/drivers/usb/gadget/u_f.h
+++ b/drivers/usb/gadget/u_f.h
@@ -47,8 +47,22 @@
 struct usb_ep;
 struct usb_request;
 
-/* Requests allocated via alloc_ep_req() must be freed by free_ep_req(). */
+/**
+ * alloc_ep_req - returns a usb_request allocated by the gadget driver and
+ * allocates the request's buffer.
+ *
+ * @ep: the endpoint to allocate a usb_request
+ * @len: usb_requests's buffer suggested size
+ * @default_len: used if @len is not provided, ie, is 0
+ *
+ * In case @ep direction is OUT, the @len will be aligned to ep's
+ * wMaxPacketSize. In order to avoid memory leaks or drops, *always* use
+ * usb_requests's length (req->length) to refer to the allocated buffer size.
+ * Requests allocated via alloc_ep_req() *must* be freed by free_ep_req().
+ */
 struct usb_request *alloc_ep_req(struct usb_ep *ep, size_t len, int default_len);
+
+/* Frees a usb_request previously allocated by alloc_ep_req() */
 static inline void free_ep_req(struct usb_ep *ep, struct usb_request *req)
 {
 	kfree(req->buf);
-- 
2.9.2