netdev - [PATCH net 2/2] netfilter: iptables: Fix potential null-ptr-deref in ip6table_nat_table

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Message-Id: <20240731213046.6194-3-pablo@netfilter.org>
Date: Wed, 31 Jul 2024 23:30:46 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netfilter-devel@...r.kernel.org
Cc: davem@...emloft.net,
	netdev@...r.kernel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	fw@...len.de
Subject: [PATCH net 2/2] netfilter: iptables: Fix potential null-ptr-deref in ip6table_nat_table_init().

From: Kuniyuki Iwashima <kuniyu@...zon.com>

ip6table_nat_table_init() accesses net->gen->ptr[ip6table_nat_net_ops.id],
but the function is exposed to user space before the entry is allocated
via register_pernet_subsys().

Let's call register_pernet_subsys() before xt_register_template().

Fixes: fdacd57c79b7 ("netfilter: x_tables: never register tables by default")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
Reviewed-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/ipv6/netfilter/ip6table_nat.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/netfilter/ip6table_nat.c b/net/ipv6/netfilter/ip6table_nat.c
index 52cf104e3478..e119d4f090cc 100644
--- a/net/ipv6/netfilter/ip6table_nat.c
+++ b/net/ipv6/netfilter/ip6table_nat.c
@@ -147,23 +147,27 @@ static struct pernet_operations ip6table_nat_net_ops = {
 
 static int __init ip6table_nat_init(void)
 {
-	int ret = xt_register_template(&nf_nat_ipv6_table,
-				       ip6table_nat_table_init);
+	int ret;
 
+	/* net->gen->ptr[ip6table_nat_net_id] must be allocated
+	 * before calling ip6t_nat_register_lookups().
+	 */
+	ret = register_pernet_subsys(&ip6table_nat_net_ops);
 	if (ret < 0)
 		return ret;
 
-	ret = register_pernet_subsys(&ip6table_nat_net_ops);
+	ret = xt_register_template(&nf_nat_ipv6_table,
+				   ip6table_nat_table_init);
 	if (ret)
-		xt_unregister_template(&nf_nat_ipv6_table);
+		unregister_pernet_subsys(&ip6table_nat_net_ops);
 
 	return ret;
 }
 
 static void __exit ip6table_nat_exit(void)
 {
-	unregister_pernet_subsys(&ip6table_nat_net_ops);
 	xt_unregister_template(&nf_nat_ipv6_table);
+	unregister_pernet_subsys(&ip6table_nat_net_ops);
 }
 
 module_init(ip6table_nat_init);
-- 
2.30.2