[PATCH 3.19.y-ckt 120/146] ipv6: do not delete previously existing ECMP routes if add fails

[Kamal Mostafa]

3.19.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Michal=20Kube=C4=8Dek?= <mkubecek at suse.cz>

commit 35f1b4e96b9258a3668872b1139c51e5a23eb876 upstream.

If adding a nexthop of an IPv6 multipath route fails, comment in
ip6_route_multipath() says we are going to delete all nexthops already
added. However, current implementation deletes even the routes it
hasn't even tried to add yet. For example, running

  ip route add 1234:5678::/64 \
      nexthop via fe80::aa dev dummy1 \
      nexthop via fe80::bb dev dummy1 \
      nexthop via fe80::cc dev dummy1

twice results in removing all routes first command added.

Limit the second (delete) run to nexthops that succeeded in the first
(add) run.

Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
Signed-off-by: Michal Kubecek <mkubecek at suse.cz>
Acked-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/ipv6/route.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 1528d84..11add92 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2446,9 +2446,9 @@ static int ip6_route_multipath(struct fib6_config *cfg, int add)
 	int attrlen;
 	int err = 0, last_err = 0;
 
+	remaining = cfg->fc_mp_len;
 beginning:
 	rtnh = (struct rtnexthop *)cfg->fc_mp;
-	remaining = cfg->fc_mp_len;
 
 	/* Parse a Multipath Entry */
 	while (rtnh_ok(rtnh, remaining)) {
@@ -2478,6 +2478,7 @@ beginning:
 				 * next hops that have been already added.
 				 */
 				add = 0;
+				remaining = cfg->fc_mp_len - remaining;
 				goto beginning;
 			}
 		}
-- 
1.9.1