ipv6: fix ECMP route replacement

mkubecek · davem330 · commit 27596472473a · 2015-05-20T12:02:26.000-04:00
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: 51ebd31 ("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/ip6_fib.c b/net/ipv6/ip6_fib.c
@@ -693,6 +693,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 {
 	struct rt6_info *iter = NULL;
 	struct rt6_info **ins;
+	struct rt6_info **fallback_ins = NULL;
 	int replace = (info->nlh &&
 		       (info->nlh->nlmsg_flags & NLM_F_REPLACE));
 	int add = (!info->nlh ||
@@ -716,8 +717,13 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 			    (info->nlh->nlmsg_flags & NLM_F_EXCL))
 				return -EEXIST;
 			if (replace) {
-				found++;
-				break;
+				if (rt_can_ecmp == rt6_qualify_for_ecmp(iter)) {
+					found++;
+					break;
+				}
+				if (rt_can_ecmp)
+					fallback_ins = fallback_ins ?: ins;
+				goto next_iter;
 			}
 
 			if (iter->dst.dev == rt->dst.dev &&
@@ -753,9 +759,17 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 		if (iter->rt6i_metric > rt->rt6i_metric)
 			break;
 
+next_iter:
 		ins = &iter->dst.rt6_next;
 	}
 
+	if (fallback_ins && !found) {
+		/* No ECMP-able route found, replace first non-ECMP one */
+		ins = fallback_ins;
+		iter = *ins;
+		found++;
+	}
+
 	/* Reset round-robin state, if necessary */
 	if (ins == &fn->leaf)
 		fn->rr_ptr = NULL;
@@ -815,6 +829,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 		}
 
 	} else {
+		int nsiblings;
+
 		if (!found) {
 			if (add)
 				goto add;
@@ -835,8 +851,27 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 			info->nl_net->ipv6.rt6_stats->fib_route_nodes++;
 			fn->fn_flags |= RTN_RTINFO;
 		}
+		nsiblings = iter->rt6i_nsiblings;
 		fib6_purge_rt(iter, fn, info->nl_net);
 		rt6_release(iter);
+
+		if (nsiblings) {
+			/* Replacing an ECMP route, remove all siblings */
+			ins = &rt->dst.rt6_next;
+			iter = *ins;
+			while (iter) {
+				if (rt6_qualify_for_ecmp(iter)) {
+					*ins = iter->dst.rt6_next;
+					fib6_purge_rt(iter, fn, info->nl_net);
+					rt6_release(iter);
+					nsiblings--;
+				} else {
+					ins = &iter->dst.rt6_next;
+				}
+				iter = *ins;
+			}
+			WARN_ON(nsiblings != 0);
+		}
 	}
 
 	return 0;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
@@ -2541,11 +2541,14 @@ static int ip6_route_multipath(struct fib6_config *cfg, int add)
 			}
 		}
 		/* 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);
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -2541,11 +2541,14 @@ static int ip6_route_multipath(struct fib6_config *cfg, int add)`
`2541`	`2541`	`}`
`2542`	`2542`	`}`
`2543`	`2543`	`/* Because each route is added like a single route we remove`
`2544`		`- * this flag after the first nexthop (if there is a collision,`
`2545`		`- * we have already fail to add the first nexthop:`
`2546`		`- * fib6_add_rt2node() has reject it).`
	`2544`	`+ * these flags after the first nexthop: if there is a collision,`
	`2545`	`+ * we have already failed to add the first nexthop:`
	`2546`	`+ * fib6_add_rt2node() has rejected it; when replacing, old`
	`2547`	`+ * nexthops have been replaced by first new, the rest should`
	`2548`	`+ * be added to it.`
`2547`	`2549`	`*/`
`2548`		`- cfg->fc_nlinfo.nlh->nlmsg_flags &= ~NLM_F_EXCL;`
	`2550`	`+ cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL \|`
	`2551`	`+ NLM_F_REPLACE);`
`2549`	`2552`	`rtnh = rtnh_next(rtnh, &remaining);`
`2550`	`2553`	`}`
`2551`	`2554`