Commit 54e6fe9d authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

ipv6: prevent infinite loop in rt6_nlmsg_size() 



While testing prior patch, I was able to trigger
an infinite loop in rt6_nlmsg_size() in the following place:

list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,
			fib6_siblings) {
	rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len);
}

This is because fib6_del_route() and fib6_add_rt2node()
uses list_del_rcu(), which can confuse rcu readers,
because they might no longer see the head of the list.

Restart the loop if f6i->fib6_nsiblings is zero.

Fixes: d9ccb18f ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250725140725.3626540-3-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ea2f921d

net/ipv6/ip6_fib.c

+2 −2
Original line number Diff line number Diff line
@@ -1265,7 +1265,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt, 
							 &rt->fib6_siblings,

							 fib6_siblings)

					sibling->fib6_nsiblings--;

				rt->fib6_nsiblings = 0;

				WRITE_ONCE(rt->fib6_nsiblings, 0);

				list_del_rcu(&rt->fib6_siblings);

				rcu_read_lock();

				rt6_multipath_rebalance(next_sibling);
@@ -2015,7 +2015,7 @@ static void fib6_del_route(struct fib6_table *table, struct fib6_node *fn, 
		list_for_each_entry_safe(sibling, next_sibling,

					 &rt->fib6_siblings, fib6_siblings)

			sibling->fib6_nsiblings--;

		rt->fib6_nsiblings = 0;

		WRITE_ONCE(rt->fib6_nsiblings, 0);

		list_del_rcu(&rt->fib6_siblings);

		rt6_multipath_rebalance(next_sibling);

	}

net/ipv6/route.c

+18 −16
Original line number Diff line number Diff line
@@ -5670,32 +5670,34 @@ static int rt6_nh_nlmsg_size(struct fib6_nh *nh, void *arg) 


static size_t rt6_nlmsg_size(struct fib6_info *f6i)

{

	struct fib6_info *sibling;

	struct fib6_nh *nh;

	int nexthop_len;



	if (f6i->nh) {

		nexthop_len = nla_total_size(4); /* RTA_NH_ID */

		nexthop_for_each_fib6_nh(f6i->nh, rt6_nh_nlmsg_size,

					 &nexthop_len);

	} else {

		struct fib6_nh *nh = f6i->fib6_nh;

		struct fib6_info *sibling;

		goto common;

	}



	rcu_read_lock();

retry:

	nh = f6i->fib6_nh;

	nexthop_len = 0;

		if (f6i->fib6_nsiblings) {

	if (READ_ONCE(f6i->fib6_nsiblings)) {

		rt6_nh_nlmsg_size(nh, &nexthop_len);



			rcu_read_lock();



		list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,

					fib6_siblings) {

			rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len);

			if (!READ_ONCE(f6i->fib6_nsiblings))

				goto retry;

		}



			rcu_read_unlock();

	}

	rcu_read_unlock();

	nexthop_len += lwtunnel_get_encap_size(nh->fib_nh_lws);

	}



common:

	return NLMSG_ALIGN(sizeof(struct rtmsg))

	       + nla_total_size(16) /* RTA_SRC */

	       + nla_total_size(16) /* RTA_DST */