nf_defrag_ipv4.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* (C) 1999-2001 Paul `Rusty' Russell
  3 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
  4 */
  5
  6#include <linux/types.h>
  7#include <linux/ip.h>
  8#include <linux/netfilter.h>
  9#include <linux/module.h>
 10#include <linux/rcupdate.h>
 11#include <linux/skbuff.h>
 12#include <net/netns/generic.h>
 13#include <net/route.h>
 14#include <net/ip.h>
 15
 16#include <linux/netfilter_bridge.h>
 17#include <linux/netfilter_ipv4.h>
 18#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
 19#if IS_ENABLED(CONFIG_NF_CONNTRACK)
 20#include <net/netfilter/nf_conntrack.h>
 21#endif
 22#include <net/netfilter/nf_conntrack_zones.h>
 23
 24static DEFINE_MUTEX(defrag4_mutex);
 25
 26static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
 27				   u_int32_t user)
 28{
 29	int err;
 30
 31	local_bh_disable();
 32	err = ip_defrag(net, skb, user);
 33	local_bh_enable();
 34
 35	if (!err)
 36		skb->ignore_df = 1;
 37
 38	return err;
 39}
 40
 41static enum ip_defrag_users nf_ct_defrag_user(unsigned int hooknum,
 42					      struct sk_buff *skb)
 43{
 44	u16 zone_id = NF_CT_DEFAULT_ZONE_ID;
 45#if IS_ENABLED(CONFIG_NF_CONNTRACK)
 46	if (skb_nfct(skb)) {
 47		enum ip_conntrack_info ctinfo;
 48		const struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 49
 50		zone_id = nf_ct_zone_id(nf_ct_zone(ct), CTINFO2DIR(ctinfo));
 51	}
 52#endif
 53	if (nf_bridge_in_prerouting(skb))
 54		return IP_DEFRAG_CONNTRACK_BRIDGE_IN + zone_id;
 55
 56	if (hooknum == NF_INET_PRE_ROUTING)
 57		return IP_DEFRAG_CONNTRACK_IN + zone_id;
 58	else
 59		return IP_DEFRAG_CONNTRACK_OUT + zone_id;
 60}
 61
 62static unsigned int ipv4_conntrack_defrag(void *priv,
 63					  struct sk_buff *skb,
 64					  const struct nf_hook_state *state)
 65{
 66	struct sock *sk = skb->sk;
 67
 68	if (sk && sk_fullsock(sk) && (sk->sk_family == PF_INET) &&
 69	    inet_test_bit(NODEFRAG, sk))
 70		return NF_ACCEPT;
 71
 72#if IS_ENABLED(CONFIG_NF_CONNTRACK)
 73#if !IS_ENABLED(CONFIG_NF_NAT)
 74	/* Previously seen (loopback)?  Ignore.  Do this before
 75	   fragment check. */
 76	if (skb_nfct(skb) && !nf_ct_is_template((struct nf_conn *)skb_nfct(skb)))
 77		return NF_ACCEPT;
 78#endif
 79	if (skb->_nfct == IP_CT_UNTRACKED)
 80		return NF_ACCEPT;
 81#endif
 82	/* Gather fragments. */
 83	if (ip_is_fragment(ip_hdr(skb))) {
 84		enum ip_defrag_users user =
 85			nf_ct_defrag_user(state->hook, skb);
 86
 87		if (nf_ct_ipv4_gather_frags(state->net, skb, user))
 88			return NF_STOLEN;
 89	}
 90	return NF_ACCEPT;
 91}
 92
 93static const struct nf_hook_ops ipv4_defrag_ops[] = {
 94	{
 95		.hook		= ipv4_conntrack_defrag,
 96		.pf		= NFPROTO_IPV4,
 97		.hooknum	= NF_INET_PRE_ROUTING,
 98		.priority	= NF_IP_PRI_CONNTRACK_DEFRAG,
 99	},
100	{
101		.hook           = ipv4_conntrack_defrag,
102		.pf             = NFPROTO_IPV4,
103		.hooknum        = NF_INET_LOCAL_OUT,
104		.priority       = NF_IP_PRI_CONNTRACK_DEFRAG,
105	},
106};
107
108static void __net_exit defrag4_net_exit(struct net *net)
109{
110	if (net->nf.defrag_ipv4_users) {
111		nf_unregister_net_hooks(net, ipv4_defrag_ops,
112					ARRAY_SIZE(ipv4_defrag_ops));
113		net->nf.defrag_ipv4_users = 0;
114	}
115}
116
117static const struct nf_defrag_hook defrag_hook = {
118	.owner = THIS_MODULE,
119	.enable = nf_defrag_ipv4_enable,
120	.disable = nf_defrag_ipv4_disable,
121};
122
123static struct pernet_operations defrag4_net_ops = {
124	.exit = defrag4_net_exit,
125};
126
127static int __init nf_defrag_init(void)
128{
129	int err;
130
131	err = register_pernet_subsys(&defrag4_net_ops);
132	if (err)
133		return err;
134
135	rcu_assign_pointer(nf_defrag_v4_hook, &defrag_hook);
136	return err;
137}
138
139static void __exit nf_defrag_fini(void)
140{
141	rcu_assign_pointer(nf_defrag_v4_hook, NULL);
142	unregister_pernet_subsys(&defrag4_net_ops);
143}
144
145int nf_defrag_ipv4_enable(struct net *net)
146{
147	int err = 0;
148
149	mutex_lock(&defrag4_mutex);
150	if (net->nf.defrag_ipv4_users == UINT_MAX) {
151		err = -EOVERFLOW;
152		goto out_unlock;
153	}
154
155	if (net->nf.defrag_ipv4_users) {
156		net->nf.defrag_ipv4_users++;
157		goto out_unlock;
158	}
159
160	err = nf_register_net_hooks(net, ipv4_defrag_ops,
161				    ARRAY_SIZE(ipv4_defrag_ops));
162	if (err == 0)
163		net->nf.defrag_ipv4_users = 1;
164
165 out_unlock:
166	mutex_unlock(&defrag4_mutex);
167	return err;
168}
169EXPORT_SYMBOL_GPL(nf_defrag_ipv4_enable);
170
171void nf_defrag_ipv4_disable(struct net *net)
172{
173	mutex_lock(&defrag4_mutex);
174	if (net->nf.defrag_ipv4_users) {
175		net->nf.defrag_ipv4_users--;
176		if (net->nf.defrag_ipv4_users == 0)
177			nf_unregister_net_hooks(net, ipv4_defrag_ops,
178						ARRAY_SIZE(ipv4_defrag_ops));
179	}
180
181	mutex_unlock(&defrag4_mutex);
182}
183EXPORT_SYMBOL_GPL(nf_defrag_ipv4_disable);
184
185module_init(nf_defrag_init);
186module_exit(nf_defrag_fini);
187
188MODULE_LICENSE("GPL");
189MODULE_DESCRIPTION("IPv4 defragmentation support");