xfrm: Generate blackhole routes only from route lookup functions

Currently we genarate a blackhole route route whenever we have
matching policies but can not resolve the states. Here we assume
that dst_output() is called to kill the balckholed packets.
Unfortunately this assumption is not true in all cases, so
it is possible that these packets leave the system unwanted.

We fix this by generating blackhole routes only from the
route lookup functions, here we can guarantee a call to
dst_output() afterwards.

Fixes: 2774c131b1d ("xfrm: Handle blackhole route creation via afinfo.")
Reported-by: Konstantinos Kolelis <k.kolelis@sirrix.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

4 files changed, 36 insertions, 7 deletions

diff --git a/include/net/dst.h b/include/net/dst.h
index 71c60f42be48..fa11c904d219 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -490,7 +490,16 @@ static inline struct dst_entry *xfrm_lookup(struct net *net,
                                             int flags)
 {
         return dst_orig;
-} 
+}
+
+static inline struct dst_entry *xfrm_lookup_route(struct net *net,
+                                                  struct dst_entry *dst_orig,
+                                                  const struct flowi *fl,
+                                                  struct sock *sk,
+                                                  int flags)
+{
+        return dst_orig;
+}
 
 static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
 {
@@ -502,6 +511,10 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
                               const struct flowi *fl, struct sock *sk,
                               int flags);
 
+struct dst_entry *xfrm_lookup_route(struct net *net, struct dst_entry *dst_orig,
+                                    const struct flowi *fl, struct sock *sk,
+                                    int flags);
+
 /* skb attached with this dst needs transformation if dst->xfrm is valid */
 static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
 {
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index eaa4b000c7b4..173e7ea54c70 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2265,9 +2265,9 @@ struct rtable *ip_route_output_flow(struct net *net, struct flowi4 *flp4,
                 return rt;
 
         if (flp4->flowi4_proto)
-                rt = (struct rtable *) xfrm_lookup(net, &rt->dst,
-                                                   flowi4_to_flowi(flp4),
-                                                   sk, 0);
+                rt = (struct rtable *)xfrm_lookup_route(net, &rt->dst,
+                                                        flowi4_to_flowi(flp4),
+                                                        sk, 0);
 
         return rt;
 }
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 315a55d66079..0a3448b2888f 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1009,7 +1009,7 @@ struct dst_entry *ip6_dst_lookup_flow(struct sock *sk, struct flowi6 *fl6,
         if (final_dst)
                 fl6->daddr = *final_dst;
 
-        return xfrm_lookup(sock_net(sk), dst, flowi6_to_flowi(fl6), sk, 0);
+        return xfrm_lookup_route(sock_net(sk), dst, flowi6_to_flowi(fl6), sk, 0);
 }
 EXPORT_SYMBOL_GPL(ip6_dst_lookup_flow);
 
@@ -1041,7 +1041,7 @@ struct dst_entry *ip6_sk_dst_lookup_flow(struct sock *sk, struct flowi6 *fl6,
         if (final_dst)
                 fl6->daddr = *final_dst;
 
-        return xfrm_lookup(sock_net(sk), dst, flowi6_to_flowi(fl6), sk, 0);
+        return xfrm_lookup_route(sock_net(sk), dst, flowi6_to_flowi(fl6), sk, 0);
 }
 EXPORT_SYMBOL_GPL(ip6_sk_dst_lookup_flow);
 
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index beeed602aeb3..7505674c9faa 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2138,7 +2138,7 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
                         xfrm_pols_put(pols, drop_pols);
                         XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTNOSTATES);
 
-                        return make_blackhole(net, family, dst_orig);
+                        return ERR_PTR(-EREMOTE);
                 }
 
                 err = -EAGAIN;
@@ -2195,6 +2195,22 @@ dropdst:
 }
 EXPORT_SYMBOL(xfrm_lookup);
 
+/* Callers of xfrm_lookup_route() must ensure a call to dst_output().
+ * Otherwise we may send out blackholed packets.
+ */
+struct dst_entry *xfrm_lookup_route(struct net *net, struct dst_entry *dst_orig,
+                                    const struct flowi *fl,
+                                    struct sock *sk, int flags)
+{
+        struct dst_entry *dst = xfrm_lookup(net, dst_orig, fl, sk, flags);
+
+        if (IS_ERR(dst) && PTR_ERR(dst) == -EREMOTE)
+                return make_blackhole(net, dst_orig->ops->family, dst_orig);
+
+        return dst;
+}
+EXPORT_SYMBOL(xfrm_lookup_route);
+
 static inline int
 xfrm_secpath_reject(int idx, struct sk_buff *skb, const struct flowi *fl)
 {