ip_tunnel: Fix a memory corruption in ip_tunnel_xmit

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 <pshelar@nicira.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index d3fbad422e0e32dbd9d7c716a3071882873b4adb..dfc6d8a3caa78211bb989bde87917f742b1af646 100644 (file)
--- 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,