From cd8d8bbd9ced4cc5d06d858f67d4aa87745e8f38 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 25 Jul 2025 14:07:23 +0000 Subject: [PATCH] ipv6: prevent infinite loop in rt6_nlmsg_size() [ Upstream commit 54e6fe9dd3b0e7c481c2228782c9494d653546da ] 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: d9ccb18f83ea ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20250725140725.3626540-3-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/ip6_fib.c | 4 ++-- net/ipv6/route.c | 38 ++++++++++++++++++++------------------ 2 files changed, 22 insertions(+), 20 deletions(-) diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index 9a1c59275a10..c53303e89390 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -1251,7 +1251,7 @@ 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); rt6_multipath_rebalance(next_sibling); return err; @@ -1969,7 +1969,7 @@ 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); } diff --git a/net/ipv6/route.c b/net/ipv6/route.c index d9ab070e78e0..f1e64c1cc49b 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -5587,32 +5587,34 @@ 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; - - nexthop_len = 0; - if (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); - } - - rcu_read_unlock(); - } - nexthop_len += lwtunnel_get_encap_size(nh->fib_nh_lws); + goto common; } + rcu_read_lock(); +retry: + nh = f6i->fib6_nh; + nexthop_len = 0; + if (READ_ONCE(f6i->fib6_nsiblings)) { + rt6_nh_nlmsg_size(nh, &nexthop_len); + + 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(); + 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 */