xfrm: introduce helper for safe determination of mtu

skb->sk socket can be of AF_INET or AF_INET6 address family. Thus we
always have to make sure we a referring to the correct interpretation
of skb->sk.

We only depend on header defines to query the mtu, so we don't introduce
a new dependency to ipv6 by this change.

Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
index 7a5491ffa4de..80baf4a3b1b5 100644
--- a/net/ipv4/xfrm4_output.c
+++ b/net/ipv4/xfrm4_output.c
@@ -21,7 +21,6 @@
 static int xfrm4_tunnel_check_size(struct sk_buff *skb)
 {
         int mtu, ret = 0;
-        struct dst_entry *dst;
 
         if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
                 goto out;
@@ -29,8 +28,7 @@ static int xfrm4_tunnel_check_size(struct sk_buff *skb)
         if (!(ip_hdr(skb)->frag_off & htons(IP_DF)) || skb->local_df)
                 goto out;
 
-        dst = skb_dst(skb);
-        mtu = dst_mtu(dst);
+        mtu = xfrm_skb_dst_mtu(skb);
         if (skb->len > mtu) {
                 if (skb->sk)
                         xfrm_local_error(skb, mtu);