Subject: [PATCH net v2 1/4] ip_tunnel: Fix a memory corruption in ip_tunnel_xmit

From: Steffen Klassert <[email-masked]>
Date: Tue, 1 Oct 2013 11:33:59 +0200

We might extend the used aera of a skb beyond the total
headroom when we install the ipip header. Fix this by
calling skb_cow_head() unconditionally.

Bug was introduced with commit c544193214
("GRE: Refactor GRE tunneling code.")

Cc: Pravin Shelar <[email-masked]>
Signed-off-by: Steffen Klassert <[email-masked]>
---

v2: Add a reference to the commit that introduced bug to the commit message

 net/ipv4/ip_tunnel.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index d3fbad4..dfc6d8a 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -642,13 +642,13 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
 
 	max_headroom = LL_RESERVED_SPACE(rt->dst.dev) + sizeof(struct iphdr)
 			+ rt->dst.header_len;
-	if (max_headroom > dev->needed_headroom) {
+	if (max_headroom > dev->needed_headroom)
 		dev->needed_headroom = max_headroom;
-		if (skb_cow_head(skb, dev->needed_headroom)) {
-			dev->stats.tx_dropped++;
-			dev_kfree_skb(skb);
-			return;
-		}
+
+	if (skb_cow_head(skb, dev->needed_headroom)) {
+		dev->stats.tx_dropped++;
+		dev_kfree_skb(skb);
+		return;
 	}
 
 	err = iptunnel_xmit(rt, skb, fl4.saddr, fl4.daddr, protocol,
-- 
1.7.9.5