Re: [PATCH net] ipv6: Do not consider linkdown nexthops during multipath

When the 'ignore_routes_with_linkdown' sysctl is set, we should not
consider linkdown nexthops during route lookup.

While the code correctly verifies that the initially selected route
('match') has a carrier, it does not perform the same check in the
subsequent multipath selection, resulting in a potential packet loss.

In case the chosen route does not have a carrier and the sysctl is set,
choose the initially selected route.

Fixes: 35103d11173b ("net: ipv6 sysctl option to ignore routes when nexthop link is down")
Signed-off-by: Ido Schimmel <redacted>
---
 net/ipv6/route.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 05eb7bc36156..0363db914c7a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -472,6 +472,11 @@ static struct rt6_info *rt6_multipath_select(struct rt6_info *match,
 				&match->rt6i_siblings, rt6i_siblings) {
 			route_choosen--;
 			if (route_choosen == 0) {
+				struct inet6_dev *idev = sibling->rt6i_idev;
+
+				if (!netif_carrier_ok(sibling->dst.dev) &&
+				    idev->cnf.ignore_routes_with_linkdown)
+					break;
 				if (rt6_score_route(sibling, oif, strict) < 0)
 					break;
 				match = sibling;