Commit b2662e75 authored by Mehul Rao's avatar Mehul Rao Committed by Jakub Kicinski
Browse files

net: nexthop: fix percpu use-after-free in remove_nh_grp_entry 



When removing a nexthop from a group, remove_nh_grp_entry() publishes
the new group via rcu_assign_pointer() then immediately frees the
removed entry's percpu stats with free_percpu(). However, the
synchronize_net() grace period in the caller remove_nexthop_from_groups()
runs after the free. RCU readers that entered before the publish still
see the old group and can dereference the freed stats via
nh_grp_entry_stats_inc() -> get_cpu_ptr(nhge->stats), causing a
use-after-free on percpu memory.

Fix by deferring the free_percpu() until after synchronize_net() in the
caller. Removed entries are chained via nh_list onto a local deferred
free list. After the grace period completes and all RCU readers have
finished, the percpu stats are safely freed.

Fixes: f4676ea7 ("net: nexthop: Add nexthop group entry stats")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMehul Rao <mehulrao@gmail.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarIdo Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260306233821.196789-1-mehulrao@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 288598d8

net/ipv4/nexthop.c

+11 −3
Original line number Diff line number Diff line
@@ -2002,7 +2002,8 @@ static void nh_hthr_group_rebalance(struct nh_group *nhg) 
}



static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,

				struct nl_info *nlinfo)

				struct nl_info *nlinfo,

				struct list_head *deferred_free)

{

	struct nh_grp_entry *nhges, *new_nhges;

	struct nexthop *nhp = nhge->nh_parent;
@@ -2062,8 +2063,8 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge, 
	rcu_assign_pointer(nhp->nh_grp, newg);



	list_del(&nhge->nh_list);

	free_percpu(nhge->stats);

	nexthop_put(nhge->nh);

	list_add(&nhge->nh_list, deferred_free);



	/* Removal of a NH from a resilient group is notified through

	 * bucket notifications.
@@ -2083,6 +2084,7 @@ static void remove_nexthop_from_groups(struct net *net, struct nexthop *nh, 
				       struct nl_info *nlinfo)

{

	struct nh_grp_entry *nhge, *tmp;

	LIST_HEAD(deferred_free);



	/* If there is nothing to do, let's avoid the costly call to

	 * synchronize_net()
@@ -2091,10 +2093,16 @@ static void remove_nexthop_from_groups(struct net *net, struct nexthop *nh, 
		return;



	list_for_each_entry_safe(nhge, tmp, &nh->grp_list, nh_list)

		remove_nh_grp_entry(net, nhge, nlinfo);

		remove_nh_grp_entry(net, nhge, nlinfo, &deferred_free);



	/* make sure all see the newly published array before releasing rtnl */

	synchronize_net();



	/* Now safe to free percpu stats — all RCU readers have finished */

	list_for_each_entry_safe(nhge, tmp, &deferred_free, nh_list) {

		list_del(&nhge->nh_list);

		free_percpu(nhge->stats);

	}

}



static void remove_nexthop_group(struct nexthop *nh, struct nl_info *nlinfo)