[PATCH v2] net: Fix behaviour of unreachable, blackhole and prohibit routes

["Nikola Forró" <nforro@redhat.com>]

Man page of ip-route(8) says following about route types:

  unreachable - these destinations are unreachable.  Packets are dis‐
  carded and the ICMP message host unreachable is generated.  The local
  senders get an EHOSTUNREACH error.

  blackhole - these destinations are unreachable.  Packets are dis‐
  carded silently.  The local senders get an EINVAL error.

  prohibit - these destinations are unreachable.  Packets are discarded
  and the ICMP message communication administratively prohibited is
  generated.  The local senders get an EACCES error.

In the inet6 address family, this was correct, except the local senders
got ENETUNREACH error instead of EHOSTUNREACH in case of unreachable route.
In the inet address family, all three route types generated ICMP message
net unreachable, and the local senders got ENETUNREACH error.

In both address families all three route types now behave consistently
with documentation.

Signed-off-by: Nikola Forró <nforro@redhat.com>
---
 include/net/ip_fib.h | 21 ++++++++++++++++-----
 net/ipv4/route.c     |  6 ++++--
 net/ipv6/route.c     |  4 +++-
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 5fa643b..cf025107 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -233,8 +233,10 @@ static inline int fib_lookup(struct net *net, const struct flowi4 *flp,
 	rcu_read_lock();
 
 	tb = fib_get_table(net, RT_TABLE_MAIN);
-	if (tb && !fib_table_lookup(tb, flp, res, flags | FIB_LOOKUP_NOREF))
-		err = 0;
+	if (tb)
+		err = fib_table_lookup(tb, flp, res, flags | FIB_LOOKUP_NOREF);
+		if (err == -EAGAIN)
+			err = -ENETUNREACH;
 
 	rcu_read_unlock();
 
@@ -267,11 +269,20 @@ static inline int fib_lookup(struct net *net, struct flowi4 *flp,
 
 	for (err = 0; !err; err = -ENETUNREACH) {
 		tb = rcu_dereference_rtnl(net->ipv4.fib_main);
-		if (tb && !fib_table_lookup(tb, flp, res, flags))
-			break;
+		if (tb) {
+			err = fib_table_lookup(tb, flp, res, flags);
+			if (!err)
+				break;
+		}
 
 		tb = rcu_dereference_rtnl(net->ipv4.fib_default);
-		if (tb && !fib_table_lookup(tb, flp, res, flags))
+		if (tb) {
+			err = fib_table_lookup(tb, flp, res, flags);
+			if (!err)
+				break;
+		}
+
+		if (err && err != -EAGAIN)
 			break;
 	}
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e681b85..4ce3f87 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2020,6 +2020,7 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
 	struct fib_result res;
 	struct rtable *rth;
 	int orig_oif;
+	int err = ENETUNREACH;
 
 	res.tclassid	= 0;
 	res.fi		= NULL;
@@ -2123,7 +2124,8 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
 		goto make_route;
 	}
 
-	if (fib_lookup(net, fl4, &res, 0)) {
+	err = fib_lookup(net, fl4, &res, 0);
+	if (err) {
 		res.fi = NULL;
 		res.table = NULL;
 		if (fl4->flowi4_oif) {
@@ -2151,7 +2153,7 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
 			res.type = RTN_UNICAST;
 			goto make_route;
 		}
-		rth = ERR_PTR(-ENETUNREACH);
+		rth = ERR_PTR(err);
 		goto out;
 	}
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d155864..d33a6a5 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1847,9 +1847,11 @@ int ip6_route_add(struct fib6_config *cfg)
 			rt->dst.input = ip6_pkt_prohibit;
 			break;
 		case RTN_THROW:
+		case RTN_UNREACHABLE:
 		default:
 			rt->dst.error = (cfg->fc_type == RTN_THROW) ? -EAGAIN
-					: -ENETUNREACH;
+					: (cfg->fc_type == RTN_UNREACHABLE)
+					? -EHOSTUNREACH : -ENETUNREACH;
 			rt->dst.output = ip6_pkt_discard_out;
 			rt->dst.input = ip6_pkt_discard;
 			break;
-- 
2.4.3