From: Eric Dumazet <edumazet@google.com> stable inclusion from stable-v6.6.102 commit e1b7932af47f92432be8303d2439d1bf77b0be23 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/ICU76G CVE: CVE-2025-38588 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ 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 <edumazet@google.com> Link: https://patch.msgid.link/20250725140725.3626540-3-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Wang Liang <wangliang74@huawei.com> --- net/ipv6/ip6_fib.c | 4 ++-- net/ipv6/route.c | 34 ++++++++++++++++++---------------- 2 files changed, 20 insertions(+), 18 deletions(-) diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index 023ac39041a2..65702bddb21f 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -1240,7 +1240,7 @@ 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; @@ -1953,7 +1953,7 @@ 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 53197087353a..41d358dd58c0 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -5577,32 +5577,34 @@ 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(); + goto common; + } - list_for_each_entry_rcu(sibling, &f6i->fib6_siblings, - fib6_siblings) { - rt6_nh_nlmsg_size(sibling->fib6_nh, &nexthop_len); - } + rcu_read_lock(); +retry: + nh = f6i->fib6_nh; + nexthop_len = 0; + if (READ_ONCE(f6i->fib6_nsiblings)) { + rt6_nh_nlmsg_size(nh, &nexthop_len); - rcu_read_unlock(); + 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; } - nexthop_len += lwtunnel_get_encap_size(nh->fib_nh_lws); } - + 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 */ -- 2.34.1