ipv6: fix ECMP route replacement
When replacing an IPv6 multipath route with "ip route replace", i.e.
NLM_F_CREATE | NLM_F_REPLACE, fib6_add_rt2node() replaces only first
matching route without fixing its siblings, resulting in corrupted
siblings linked list; removing one of the siblings can then end in an
infinite loop.
IPv6 ECMP implementation is a bit different from IPv4 so that route
replacement cannot work in exactly the same way. This should be a
reasonable approximation:
1. If the new route is ECMP-able and there is a matching ECMP-able one
already, replace it and all its siblings (if any).
2. If the new route is ECMP-able and no matching ECMP-able route exists,
replace first matching non-ECMP-able (if any) or just add the new one.
3. If the new route is not ECMP-able, replace first matching
non-ECMP-able route (if any) or add the new route.
We also need to remove the NLM_F_REPLACE flag after replacing old
route(s) by first nexthop of an ECMP route so that each subsequent
nexthop does not replace previous one.
Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 3821a35..c73ae50 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2541,11 +2541,14 @@
}
}
/* Because each route is added like a single route we remove
- * this flag after the first nexthop (if there is a collision,
- * we have already fail to add the first nexthop:
- * fib6_add_rt2node() has reject it).
+ * these flags after the first nexthop: if there is a collision,
+ * we have already failed to add the first nexthop:
+ * fib6_add_rt2node() has rejected it; when replacing, old
+ * nexthops have been replaced by first new, the rest should
+ * be added to it.
*/
- cfg->fc_nlinfo.nlh->nlmsg_flags &= ~NLM_F_EXCL;
+ cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
+ NLM_F_REPLACE);
rtnh = rtnh_next(rtnh, &remaining);
}