Subject: [PATCH net] gianfar: simplify FCS handling and fix memory leak

From: Andy Spencer <[email-masked]>
Date: Thu, 22 Feb 2018 11:05:33 -0800

Previously, buffer descriptors containing only the frame check sequence
(FCS) were skipped and not added to the skb. However, the page reference
count was still incremented, leading to a memory leak.

Fixing this inside gfar_add_rx_frag() is difficult due to reserved
memory handling and page reuse. Instead, move the FCS handling to
gfar_process_frame() and trim off the FCS before passing the skb up the
networking stack.

Signed-off-by: Andy Spencer <[email-masked]>
Signed-off-by: Jim Gruen <[email-masked]>
---
 drivers/net/ethernet/freescale/gianfar.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index 3bdeb29..f5c87bd3 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -2934,29 +2934,17 @@ static bool gfar_add_rx_frag(struct gfar_rx_buff *rxb, u32 lstatus,
 {
 	int size = lstatus & BD_LENGTH_MASK;
 	struct page *page = rxb->page;
-	bool last = !!(lstatus & BD_LFLAG(RXBD_LAST));
-
-	/* Remove the FCS from the packet length */
-	if (last)
-		size -= ETH_FCS_LEN;
 
 	if (likely(first)) {
 		skb_put(skb, size);
 	} else {
 		/* the last fragments' length contains the full frame length */
-		if (last)
+		if (lstatus & BD_LFLAG(RXBD_LAST))
 			size -= skb->len;
 
-		/* Add the last fragment if it contains something other than
-		 * the FCS, otherwise drop it and trim off any part of the FCS
-		 * that was already received.
-		 */
-		if (size > 0)
-			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
-					rxb->page_offset + RXBUF_ALIGNMENT,
-					size, GFAR_RXB_TRUESIZE);
-		else if (size < 0)
-			pskb_trim(skb, skb->len + size);
+		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
+				rxb->page_offset + RXBUF_ALIGNMENT,
+				size, GFAR_RXB_TRUESIZE);
 	}
 
 	/* try reuse page */
@@ -3069,6 +3057,9 @@ static void gfar_process_frame(struct net_device *ndev, struct sk_buff *skb)
 	if (priv->padding)
 		skb_pull(skb, priv->padding);
 
+	/* Trim off the FCS */
+	pskb_trim(skb, skb->len - ETH_FCS_LEN);
+
 	if (ndev->features & NETIF_F_RXCSUM)
 		gfar_rx_checksum(skb, fcb);
 
-- 
2.7.4