[PATCH hyperv-fixes] hv_netvsc: Fix IP header checksum for coalesced packets

[Haiyang Zhang]

From: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>

Incoming packets may have IP header checksum verified by the host.
They may not have IP header checksum computed after coalescing.
This patch re-compute the checksum when necessary, otherwise the
packets may be dropped, because Linux network stack always checks it.

Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
---
 drivers/net/hyperv/netvsc_drv.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 256adbd044f5..cf4897043e83 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -744,6 +744,14 @@ void netvsc_linkstatus_callback(struct net_device *net,
 	schedule_delayed_work(&ndev_ctx->dwork, 0);
 }
 
+static void netvsc_comp_ipcsum(struct sk_buff *skb)
+{
+	struct iphdr *iph = (struct iphdr *)skb->data;
+
+	iph->check = 0;
+	iph->check = ip_fast_csum(iph, iph->ihl);
+}
+
 static struct sk_buff *netvsc_alloc_recv_skb(struct net_device *net,
 					     struct netvsc_channel *nvchan)
 {
@@ -770,9 +778,17 @@ static struct sk_buff *netvsc_alloc_recv_skb(struct net_device *net,
 	/* 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.
+	/* Incoming packets may have IP header checksum verified by the host.
+	 * They may not have IP header checksum computed after coalescing.
+	 * We compute it here if the flags are set, because on Linux, the IP
+	 * checksum is always checked.
+	 */
+	if (csum_info && csum_info->receive.ip_checksum_value_invalid &&
+	    csum_info->receive.ip_checksum_succeeded &&
+	    skb->protocol == htons(ETH_P_IP))
+		netvsc_comp_ipcsum(skb);
+
+	/* Do L4 checksum offload if enabled and present.
 	 */
 	if (csum_info && (net->features & NETIF_F_RXCSUM)) {
 		if (csum_info->receive.tcp_checksum_succeeded ||
-- 
2.19.1