linux-kernel - [PATCH 4.8 27/35] netvsc: fix incorrect receive checksum offloading

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Date:   Sun, 13 Nov 2016 12:27:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Stephen Hemminger <sthemmin@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.8 27/35] netvsc: fix incorrect receive checksum offloading

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Hemminger <sthemmin@...rosoft.com>


[ Upstream commit e52fed7177f74382f742c27de2cc5314790aebb6 ]

The Hyper-V netvsc driver was looking at the incorrect status bits
in the checksum info. It was setting the receive checksum unnecessary
flag based on the IP header checksum being correct. The checksum
flag is skb is about TCP and UDP checksum status. Because of this
bug, any packet received with bad TCP checksum would be passed
up the stack and to the application causing data corruption.
The problem is reproducible via netcat and netem.

This had a side effect of not doing receive checksum offload
on IPv6. The driver was also also always doing checksum offload
independent of the checksum setting done via ethtool.

Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/hyperv/netvsc_drv.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -624,15 +624,18 @@ static struct sk_buff *netvsc_alloc_recv
 	       packet->total_data_buflen);
 
 	skb->protocol = eth_type_trans(skb, net);
-	if (csum_info) {
-		/* We only look at the IP checksum here.
-		 * Should we be dropping the packet if checksum
-		 * failed? How do we deal with other checksums - TCP/UDP?
-		 */
-		if (csum_info->receive.ip_checksum_succeeded)
+
+	/* skb is already created with CHECKSUM_NONE */
+	skb_checksum_none_assert(skb);
+
+	/*
+	 * In Linux, the IP checksum is always checked.
+	 * Do L4 checksum offload if enabled and present.
+	 */
+	if (csum_info && (net->features & NETIF_F_RXCSUM)) {
+		if (csum_info->receive.tcp_checksum_succeeded ||
+		    csum_info->receive.udp_checksum_succeeded)
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
-		else
-			skb->ip_summed = CHECKSUM_NONE;
 	}
 
 	if (vlan_tci & VLAN_TAG_PRESENT)