ip6_tunnel: fix possible use-after-free on xmit

BugLink: https://bugs.launchpad.net/bugs/1840378
[ Upstream commit 01f5bffad555f8e22a61f4b1261fe09cf1b96994 ]

ip4ip6/ip6ip6 tunnels run iptunnel_handle_offloads on xmit which
can cause a possible use-after-free accessing iph/ipv6h pointer
since the packet will be 'uncloned' running pskb_expand_head if
it is a cloned gso skb.

Fixes: 0e9a709560db ("ip6_tunnel, ip6_gre: fix setting of DSCP on encapsulated packets")
Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 20a918e9e9f3b1b1090b6e9feff75f6c89f16e22..bd93977eb7933b54f5fc9362affba2db933b3bdf 100644 (file)
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1268,12 +1268,11 @@ ip4ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
        }
 
        fl6.flowi6_uid = sock_net_uid(dev_net(dev), NULL);
+       dsfield = INET_ECN_encapsulate(dsfield, ipv4_get_dsfield(iph));
 
        if (iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6))
                return -1;
 
-       dsfield = INET_ECN_encapsulate(dsfield, ipv4_get_dsfield(iph));
-
        skb_set_inner_ipproto(skb, IPPROTO_IPIP);
 
        err = ip6_tnl_xmit(skb, dev, dsfield, &fl6, encap_limit, &mtu,
@@ -1356,12 +1355,11 @@ ip6ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
        }
 
        fl6.flowi6_uid = sock_net_uid(dev_net(dev), NULL);
+       dsfield = INET_ECN_encapsulate(dsfield, ipv6_get_dsfield(ipv6h));
 
        if (iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6))
                return -1;
 
-       dsfield = INET_ECN_encapsulate(dsfield, ipv6_get_dsfield(ipv6h));
-
        skb_set_inner_ipproto(skb, IPPROTO_IPV6);
 
        err = ip6_tnl_xmit(skb, dev, dsfield, &fl6, encap_limit, &mtu,