[PATCH net 07/11] netfilter: nat: use kfree_rcu to release ops

Pablo Neira Ayuso
2026-04-16T13:15:11Z

Florian Westphal says:

"Historically this is not an issue, even for normal base hooks: the data
path doesn't use the original nf_hook_ops that are used to register the
callbacks.

However, in v5.14 I added the ability to dump the active netfilter
hooks from userspace.

This code will peek back into the nf_hook_ops that are available
at the tail of the pointer-array blob used by the datapath.

The nat hooks are special, because they are called indirectly from
the central nat dispatcher hook. They are currently invisible to
the nfnl hook dump subsystem though.

But once that changes the nat ops structures have to be deferred too."

Update nf_nat_register_fn() to deal with partial exposition of the hooks
from error path which can be also an issue for nfnetlink_hook.

Fixes: e2cf17d3774c ("netfilter: add new hook nfnl subsystem")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
net/ipv4/netfilter/iptable_nat.c | 2 +-
net/ipv6/netfilter/ip6table_nat.c | 2 +-
net/netfilter/nf_nat_core.c | 10 ++++++----
3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/netfilter/iptable_nat.c b/net/ipv4/netfilter/iptable_nat.c
index a5db7c67d61b..3b1de7f82bf8 100644
--- a/net/ipv4/netfilter/iptable_nat.c
+++ b/net/ipv4/netfilter/iptable_nat.c
@@ -100,7 +100,7 @@ static void ipt_nat_unregister_lookups(struct net *net)
for (i = 0; i < ARRAY_SIZE(nf_nat_ipv4_ops); i++)
nf_nat_ipv4_unregister_fn(net, &ops[i]);

- kfree(ops);
+ kfree_rcu(ops, rcu);
}

static int iptable_nat_table_init(struct net *net)
diff --git a/net/ipv6/netfilter/ip6table_nat.c b/net/ipv6/netfilter/ip6table_nat.c
index e119d4f090cc..9adfbfeaab0c 100644
--- a/net/ipv6/netfilter/ip6table_nat.c
+++ b/net/ipv6/netfilter/ip6table_nat.c
@@ -102,7 +102,7 @@ static void ip6t_nat_unregister_lookups(struct net *net)
for (i = 0; i < ARRAY_SIZE(nf_nat_ipv6_ops); i++)
nf_nat_ipv6_unregister_fn(net, &ops[i]);

- kfree(ops);
+ kfree_rcu(ops, rcu);
}

static int ip6table_nat_table_init(struct net *net)
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 3b5434e4ec9c..b30ca94c2bb7 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -1228,9 +1228,11 @@ int nf_nat_register_fn(struct net *net, u8 pf, const struct nf_hook_ops *ops,
ret = nf_register_net_hooks(net, nat_ops, ops_count);
if (ret < 0) {
mutex_unlock(&nf_nat_proto_mutex);
- for (i = 0; i < ops_count; i++)
- kfree(nat_ops[i].priv);
- kfree(nat_ops);
+ for (i = 0; i < ops_count; i++) {
+ priv = nat_ops[i].priv;
+ kfree_rcu(priv, rcu_head);
+ }
+ kfree_rcu(nat_ops, rcu);
return ret;
}

@@ -1294,7 +1296,7 @@ void nf_nat_unregister_fn(struct net *net, u8 pf, const struct nf_hook_ops *ops,
}

nat_proto_net->nat_hook_ops = NULL;
- kfree(nat_ops);
+ kfree_rcu(nat_ops, rcu);
}
unlock:
mutex_unlock(&nf_nat_proto_mutex);
--
2.47.3