From: Xiang Mei (Microsoft) Date: Wed, 22 Jul 2026 00:29:51 +0000 (+0000) Subject: nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4787a6d2629b4e8c0b6bacab1f75c1660eca44d9;p=thirdparty%2Fkernel%2Fstable.git nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush nh_rt_cache_flush() walks nh->f6i_list during an RTNL-serialized nexthop replace without holding nh->lock, racing the unlocked IPv6 route add/delete that mutate the list under nh->lock and free fib6_info entries (nh_rt_cache_flush() is inlined into rtm_new_nexthop()): BUG: KASAN: slab-use-after-free in nh_rt_cache_flush (net/ipv4/nexthop.c:2243) Read of size 8 at addr ffff888012953e18 by task exploit/146 nh_rt_cache_flush (net/ipv4/nexthop.c:2243) replace_nexthop (net/ipv4/nexthop.c:2610) rtm_new_nexthop (net/ipv4/nexthop.c:3323) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) Unlike the other f6i_list walks, this one bumps each route's sernum via fib6_update_sernum_upto_root(), which needs tb6_lock; taking nh->lock around it would invert the established tb6_lock -> nh->lock order and deadlock. As the only purpose is to invalidate cached dsts, bump the IPv6 sernum for the whole netns with rt_genid_bump_ipv6() instead, mirroring the rt_cache_flush() already done for IPv4 just above. Fixes: 081efd18326e ("ipv6: Protect nh->f6i_list with spinlock and flag.") Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Xiang Mei (Microsoft) Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260722002951.2614721-2-xmei5@asu.edu Signed-off-by: Jakub Kicinski --- diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c index eb5c76ac807b..0f1e21a5c812 100644 --- a/net/ipv4/nexthop.c +++ b/net/ipv4/nexthop.c @@ -2240,18 +2240,18 @@ static void remove_one_nexthop(struct net *net, struct nexthop *nh, static void nh_rt_cache_flush(struct net *net, struct nexthop *nh, struct nexthop *replaced_nh) { - struct fib6_info *f6i; struct nh_group *nhg; + bool have_f6i; int i; if (!list_empty(&nh->fi_list)) rt_cache_flush(net); - list_for_each_entry(f6i, &nh->f6i_list, nh_list) { - spin_lock_bh(&f6i->fib6_table->tb6_lock); - fib6_update_sernum_upto_root(net, f6i); - spin_unlock_bh(&f6i->fib6_table->tb6_lock); - } + spin_lock_bh(&nh->lock); + have_f6i = !list_empty(&nh->f6i_list); + spin_unlock_bh(&nh->lock); + if (have_f6i) + rt_genid_bump_ipv6(net); /* if an IPv6 group was replaced, we have to release all old * dsts to make sure all refcounts are released