xfrm: make local error reporting more robust

In xfrm4 and xfrm6 we need to take care about sockets of the other
address family. This could happen because a 6in4 or 4in6 tunnel could
get protected by ipsec.

Because we don't want to have a run-time dependency on ipv6 when only
using ipv4 xfrm we have to embed a pointer to the correct local_error
function in xfrm_state_afinet and look it up when returning an error
depending on the socket address family.

Thanks to vi0ss for the great bug report:
<https://bugzilla.kernel.org/show_bug.cgi?id=58691>

v2:
a) fix two more unsafe interpretations of skb->sk as ipv6 socket
   (xfrm6_local_dontfrag and __xfrm6_output)
v3:
a) add an EXPORT_SYMBOL_GPL(xfrm_local_error) to fix a link error when
   building ipv6 as a module (thanks to Steffen Klassert)

Reported-by: <vi0oss@gmail.com>
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>

2 files changed, 7 insertions, 4 deletions

diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
index 8755a3079d0f..b64fff30eb06 100644
--- a/net/ipv6/xfrm6_output.c
+++ b/net/ipv6/xfrm6_output.c
@@ -34,8 +34,10 @@ static int xfrm6_local_dontfrag(struct sk_buff *skb)
         struct sock *sk = skb->sk;
 
         if (sk) {
-                proto = sk->sk_protocol;
+                if (sk->sk_family != AF_INET6)
+                        return 0;
 
+                proto = sk->sk_protocol;
                 if (proto == IPPROTO_UDP || proto == IPPROTO_RAW)
                         return inet6_sk(sk)->dontfrag;
         }
@@ -54,7 +56,7 @@ static void xfrm6_local_rxpmtu(struct sk_buff *skb, u32 mtu)
         ipv6_local_rxpmtu(sk, &fl6, mtu);
 }
 
-static void xfrm6_local_error(struct sk_buff *skb, u32 mtu)
+void xfrm6_local_error(struct sk_buff *skb, u32 mtu)
 {
         struct flowi6 fl6;
         struct sock *sk = skb->sk;
@@ -80,7 +82,7 @@ static int xfrm6_tunnel_check_size(struct sk_buff *skb)
                 if (xfrm6_local_dontfrag(skb))
                         xfrm6_local_rxpmtu(skb, mtu);
                 else if (skb->sk)
-                        xfrm6_local_error(skb, mtu);
+                        xfrm_local_error(skb, mtu);
                 else
                         icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
                 ret = -EMSGSIZE;
@@ -142,7 +144,7 @@ static int __xfrm6_output(struct sk_buff *skb)
                 xfrm6_local_rxpmtu(skb, mtu);
                 return -EMSGSIZE;
         } else if (!skb->local_df && skb->len > mtu && skb->sk) {
-                xfrm6_local_error(skb, mtu);
+                xfrm_local_error(skb, mtu);
                 return -EMSGSIZE;
         }
 
diff --git a/net/ipv6/xfrm6_state.c b/net/ipv6/xfrm6_state.c
index d8c70b8efc24..3fc970135fc6 100644
--- a/net/ipv6/xfrm6_state.c
+++ b/net/ipv6/xfrm6_state.c
@@ -183,6 +183,7 @@ static struct xfrm_state_afinfo xfrm6_state_afinfo = {
         .extract_input          = xfrm6_extract_input,
         .extract_output         = xfrm6_extract_output,
         .transport_finish       = xfrm6_transport_finish,
+        .local_error            = xfrm6_local_error,
 };
 
 int __init xfrm6_state_init(void)