rt2x00: Preserve descriptor information after memmove()

Due to usage of memmove() in rt2x00usb the descriptor can become
corrupted because it is being overwritten by the data part.
Overall having the descriptor in front of the frame is a bad idea,
we can however use the skb->cb array for this task, since that
contains more then enough room to hold the entire descriptor and
preserve the information long enough.

After this we can also cleanup the alignment code a bit to make it
work a bit more flexible to allow for all kinds of odd header lengths.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 42 insertions, 18 deletions

diff --git a/drivers/net/wireless/rt2x00/rt2x00usb.c b/drivers/net/wireless/rt2x00/rt2x00usb.c
index caee65e8219..f72b3d07a42 100644
--- a/drivers/net/wireless/rt2x00/rt2x00usb.c
+++ b/drivers/net/wireless/rt2x00/rt2x00usb.c
@@ -246,22 +246,35 @@ static struct sk_buff* rt2x00usb_alloc_rxskb(struct data_queue *queue)
 {
 	struct sk_buff *skb;
 	unsigned int frame_size;
+	unsigned int reserved_size;
 
 	/*
-	 * As alignment we use 2 and not NET_IP_ALIGN because we need
-	 * to be sure we have 2 bytes room in the head. (NET_IP_ALIGN
-	 * can be 0 on some hardware). We use these 2 bytes for frame
-	 * alignment later, we assume that the chance that
-	 * header_size % 4 == 2 is bigger then header_size % 2 == 0
-	 * and thus optimize alignment by reserving the 2 bytes in
-	 * advance.
+	 * The frame size includes descriptor size, because the
+	 * hardware directly receive the frame into the skbuffer.
 	 */
 	frame_size = queue->data_size + queue->desc_size;
-	skb = dev_alloc_skb(queue->desc_size + frame_size + 2);
+
+	/*
+	 * For the allocation we should keep a few things in mind:
+	 * 1) 4byte alignment of 802.11 payload
+	 *
+	 * For (1) we need at most 4 bytes to guarentee the correct
+	 * alignment. We are going to optimize the fact that the chance
+	 * that the 802.11 header_size % 4 == 2 is much bigger then
+	 * anything else. However since we need to move the frame up
+	 * to 3 bytes to the front, which means we need to preallocate
+	 * 6 bytes.
+	 */
+	reserved_size = 6;
+
+	/*
+	 * Allocate skbuffer.
+	 */
+	skb = dev_alloc_skb(frame_size + reserved_size);
 	if (!skb)
 		return NULL;
 
-	skb_reserve(skb, queue->desc_size + 2);
+	skb_reserve(skb, reserved_size);
 	skb_put(skb, frame_size);
 
 	return skb;
@@ -274,7 +287,8 @@ static void rt2x00usb_interrupt_rxdone(struct urb *urb)
 	struct sk_buff *skb;
 	struct skb_frame_desc *skbdesc;
 	struct rxdone_entry_desc rxdesc;
-	int header_size;
+	unsigned int header_size;
+	unsigned int align;
 
 	if (!test_bit(DEVICE_ENABLED_RADIO, &rt2x00dev->flags) ||
 	    !test_and_clear_bit(ENTRY_OWNER_DEVICE_DATA, &entry->flags))
@@ -298,19 +312,29 @@ static void rt2x00usb_interrupt_rxdone(struct urb *urb)
 	memset(&rxdesc, 0, sizeof(rxdesc));
 	rt2x00dev->ops->lib->fill_rxdone(entry, &rxdesc);
 
+	header_size = ieee80211_get_hdrlen_from_skb(entry->skb);
+
 	/*
 	 * The data behind the ieee80211 header must be
-	 * aligned on a 4 byte boundary.
+	 * aligned on a 4 byte boundary. We already reserved
+	 * 2 bytes for header_size % 4 == 2 optimization.
+	 * To determine the number of bytes which the data
+	 * should be moved to the left, we must add these
+	 * 2 bytes to the header_size.
 	 */
-	header_size = ieee80211_get_hdrlen_from_skb(entry->skb);
-	if (header_size % 4 == 0) {
-		skb_push(entry->skb, 2);
-		memmove(entry->skb->data, entry->skb->data + 2,
-			entry->skb->len - 2);
-		skbdesc->data = entry->skb->data;
-		skb_trim(entry->skb,entry->skb->len - 2);
+	align = (header_size + 2) % 4;
+
+	if (align) {
+		skb_push(entry->skb, align);
+		/* Move entire frame in 1 command */
+		memmove(entry->skb->data, entry->skb->data + align,
+			rxdesc.size);
 	}
 
+	/* Update data pointers, trim buffer to correct size */
+	skbdesc->data = entry->skb->data;
+	skb_trim(entry->skb, rxdesc.size);
+
 	/*
 	 * Allocate a new sk buffer to replace the current one.
 	 * If allocation fails, we should drop the current frame