From dc58fb98fe1041e61cddb174f53ba195942d6375 Mon Sep 17 00:00:00 2001
From: t_jeang <devnull@localhost>
Date: Tue, 6 Jan 2009 12:06:02 +0000
Subject: [PATCH] It turns out that Windows occasionally generates packets in
 which the IP and TCP headers are in different fragments.  Make sure that the
 backends can handle this.

---
 drivers/xen/netback/xenbus.c | 10 ++++++++++
 net/core/dev.c               | 18 +++++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/netback/xenbus.c b/drivers/xen/netback/xenbus.c
index a7835068..774da6df 100644
--- a/drivers/xen/netback/xenbus.c
+++ b/drivers/xen/netback/xenbus.c
@@ -112,6 +112,16 @@ static int netback_probe(struct xenbus_device *dev,
 			goto abort_transaction;
 		}
 
+		/* We can cope with transmit checksum offload packets
+		   in which the TCP and IP headers are in separate
+		   fragments. */
+		err = xenbus_printf(xbt, dev->nodename,
+				    "feature-tx-csum-split-header", "%d", 1);
+		if (err) {
+			message = "writing feature-tx-csum-split-header";
+			goto abort_transaction;
+		}
+
 		/*
 		 * We don't support rx-flip path (except old guests who don't
 		 * grok this feature flag).
diff --git a/net/core/dev.c b/net/core/dev.c
index be9c3f93..82d94393 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1399,14 +1399,26 @@ out_kfree_skb:
 }
 
 #ifdef CONFIG_XEN
+static int skb_pull_up_to(struct sk_buff *skb, void *ptr)
+{
+	if (ptr < (void *)skb->tail)
+		return 1;
+	if (__pskb_pull_tail(skb,
+			     ptr - (void *)skb->data - skb_headlen(skb))) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
 inline int skb_checksum_setup(struct sk_buff *skb)
 {
 	if (skb->proto_csum_blank) {
 		if (skb->protocol != htons(ETH_P_IP))
 			goto out;
-		skb->h.raw = (unsigned char *)skb->nh.iph + 4*skb->nh.iph->ihl;
-		if (skb->h.raw >= skb->tail)
+		if (!skb_pull_up_to(skb, skb->nh.iph + 1))
 			goto out;
+		skb->h.raw = (unsigned char *)skb->nh.iph + 4*skb->nh.iph->ihl;
 		switch (skb->nh.iph->protocol) {
 		case IPPROTO_TCP:
 			skb->csum = offsetof(struct tcphdr, check);
@@ -1421,7 +1433,7 @@ inline int skb_checksum_setup(struct sk_buff *skb)
 				       " %d packet", skb->nh.iph->protocol);
 			goto out;
 		}
-		if ((skb->h.raw + skb->csum + 2) > skb->tail)
+		if (!skb_pull_up_to(skb, skb->h.raw + skb->csum + 2))
 			goto out;
 		skb->ip_summed = CHECKSUM_HW;
 		skb->proto_csum_blank = 0;
-- 
2.39.5