netdev - [PATCH net] ipv6: Revert "ipv6: Allow non-gateway ECMP for IPv6"

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Message-Id: <20180502194156.9275-1-idosch@mellanox.com>
Date:   Wed,  2 May 2018 22:41:56 +0300
From:   Ido Schimmel <idosch@...lanox.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, dsahern@...il.com, eric.dumazet@...il.com,
        Thomas.Winter@...iedtelesis.co.nz, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: [PATCH net] ipv6: Revert "ipv6: Allow non-gateway ECMP for IPv6"

This reverts commit edd7ceb78296 ("ipv6: Allow non-gateway ECMP for
IPv6").

Eric reported a division by zero in rt6_multipath_rebalance() which is
caused by above commit that considers identical local routes to be
siblings. The division by zero happens because a nexthop weight is not
set for local routes.

Revert the commit as it does not fix a bug and has side effects.

To reproduce:

# ip -6 address add 2001:db8::1/64 dev dummy0
# ip -6 address add 2001:db8::1/64 dev dummy1

Fixes: edd7ceb78296 ("ipv6: Allow non-gateway ECMP for IPv6")
Signed-off-by: Ido Schimmel <idosch@...lanox.com>
Reported-by: Eric Dumazet <eric.dumazet@...il.com>
---
 include/net/ip6_route.h | 3 ++-
 net/ipv6/ip6_fib.c      | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index abceb5864d99..08b132381984 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -68,7 +68,8 @@ static inline bool rt6_need_strict(const struct in6_addr *daddr)
 
 static inline bool rt6_qualify_for_ecmp(const struct rt6_info *rt)
 {
-	return (rt->rt6i_flags & (RTF_ADDRCONF | RTF_DYNAMIC)) == 0;
+	return (rt->rt6i_flags & (RTF_GATEWAY|RTF_ADDRCONF|RTF_DYNAMIC)) ==
+	       RTF_GATEWAY;
 }
 
 void ip6_route_input(struct sk_buff *skb);
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 3c97c29d4401..deab2db6692e 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -934,6 +934,9 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 			 * list.
 			 * Only static routes (which don't have flag
 			 * RTF_EXPIRES) are used for ECMPv6.
+			 *
+			 * To avoid long list, we only had siblings if the
+			 * route have a gateway.
 			 */
 			if (rt_can_ecmp &&
 			    rt6_qualify_for_ecmp(iter))
-- 
2.14.3