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>

5 files changed, 25 insertions, 12 deletions

diff --git a/include/net/route.h b/include/net/route.h
index 2ea40c1b5e00..afdeeb5bec25 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -317,4 +317,12 @@ static inline int ip4_dst_hoplimit(const struct dst_entry *dst)
         return hoplimit;
 }
 
+static inline int ip_skb_dst_mtu(struct sk_buff *skb)
+{
+        struct inet_sock *inet = skb->sk ? inet_sk(skb->sk) : NULL;
+
+        return (inet && inet->pmtudisc == IP_PMTUDISC_PROBE) ?
+               skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));
+}
+
 #endif  /* _ROUTE_H */
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index e823786e7c66..b41d2d10ff0e 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -20,6 +20,7 @@
 #include <net/route.h>
 #include <net/ipv6.h>
 #include <net/ip6_fib.h>
+#include <net/ip6_route.h>
 #include <net/flow.h>
 
 #include <linux/interrupt.h>
@@ -1723,4 +1724,15 @@ static inline int xfrm_mark_put(struct sk_buff *skb, const struct xfrm_mark *m)
         return ret;
 }
 
+static inline int xfrm_skb_dst_mtu(struct sk_buff *skb)
+{
+        struct sock *sk = skb->sk;
+
+        if (sk && sk->sk_family == AF_INET6)
+                return ip6_skb_dst_mtu(skb);
+        else if (sk && sk->sk_family == AF_INET)
+                return ip_skb_dst_mtu(skb);
+        return dst_mtu(skb_dst(skb));
+}
+
 #endif  /* _NET_XFRM_H */
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 4bcabf3ab4ca..9ee17e3d11c3 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -211,14 +211,6 @@ static inline int ip_finish_output2(struct sk_buff *skb)
         return -EINVAL;
 }
 
-static inline int ip_skb_dst_mtu(struct sk_buff *skb)
-{
-        struct inet_sock *inet = skb->sk ? inet_sk(skb->sk) : NULL;
-
-        return (inet && inet->pmtudisc == IP_PMTUDISC_PROBE) ?
-               skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));
-}
-
 static int ip_finish_output(struct sk_buff *skb)
 {
 #if defined(CONFIG_NETFILTER) && defined(CONFIG_XFRM)
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);
diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
index b64fff30eb06..3ac5ab264fed 100644
--- a/net/ipv6/xfrm6_output.c
+++ b/net/ipv6/xfrm6_output.c
@@ -138,7 +138,10 @@ static int __xfrm6_output(struct sk_buff *skb)
 {
         struct dst_entry *dst = skb_dst(skb);
         struct xfrm_state *x = dst->xfrm;
-        int mtu = ip6_skb_dst_mtu(skb);
+        int mtu = xfrm_skb_dst_mtu(skb);
+
+        if (mtu < IPV6_MIN_MTU)
+                mtu = IPV6_MIN_MTU;
 
         if (skb->len > mtu && xfrm6_local_dontfrag(skb)) {
                 xfrm6_local_rxpmtu(skb, mtu);