1/*
2 * IPv4 specific functions of netfilter core
3 *
4 * Rusty Russell (C) 2000 -- This code is GPL.
5 * Patrick McHardy (C) 2006-2012
6 */
7#include <linux/kernel.h>
8#include <linux/netfilter.h>
9#include <linux/netfilter_ipv4.h>
10#include <linux/ip.h>
11#include <linux/skbuff.h>
12#include <linux/gfp.h>
13#include <linux/export.h>
14#include <net/route.h>
15#include <net/xfrm.h>
16#include <net/ip.h>
17#include <net/netfilter/nf_queue.h>
18
19/* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
20int ip_route_me_harder(struct sk_buff *skb, unsigned int addr_type)
21{
22	struct net *net = dev_net(skb_dst(skb)->dev);
23	const struct iphdr *iph = ip_hdr(skb);
24	struct rtable *rt;
25	struct flowi4 fl4 = {};
26	__be32 saddr = iph->saddr;
27	__u8 flags = skb->sk ? inet_sk_flowi_flags(skb->sk) : 0;
28	unsigned int hh_len;
29
30	if (addr_type == RTN_UNSPEC)
31		addr_type = inet_addr_type(net, saddr);
32	if (addr_type == RTN_LOCAL || addr_type == RTN_UNICAST)
33		flags |= FLOWI_FLAG_ANYSRC;
34	else
35		saddr = 0;
36
37	/* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
38	 * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
39	 */
40	fl4.daddr = iph->daddr;
41	fl4.saddr = saddr;
42	fl4.flowi4_tos = RT_TOS(iph->tos);
43	fl4.flowi4_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
44	fl4.flowi4_mark = skb->mark;
45	fl4.flowi4_flags = flags;
46	rt = ip_route_output_key(net, &fl4);
47	if (IS_ERR(rt))
48		return PTR_ERR(rt);
49
50	/* Drop old route. */
51	skb_dst_drop(skb);
52	skb_dst_set(skb, &rt->dst);
53
54	if (skb_dst(skb)->error)
55		return skb_dst(skb)->error;
56
57#ifdef CONFIG_XFRM
58	if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
59	    xfrm_decode_session(skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
60		struct dst_entry *dst = skb_dst(skb);
61		skb_dst_set(skb, NULL);
62		dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), skb->sk, 0);
63		if (IS_ERR(dst))
64			return PTR_ERR(dst);;
65		skb_dst_set(skb, dst);
66	}
67#endif
68
69	/* Change in oif may mean change in hh_len. */
70	hh_len = skb_dst(skb)->dev->hard_header_len;
71	if (skb_headroom(skb) < hh_len &&
72	    pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
73				0, GFP_ATOMIC))
74		return -ENOMEM;
75
76	return 0;
77}
78EXPORT_SYMBOL(ip_route_me_harder);
79
80/*
81 * Extra routing may needed on local out, as the QUEUE target never
82 * returns control to the table.
83 */
84
85struct ip_rt_info {
86	__be32 daddr;
87	__be32 saddr;
88	u_int8_t tos;
89	u_int32_t mark;
90};
91
92static void nf_ip_saveroute(const struct sk_buff *skb,
93			    struct nf_queue_entry *entry)
94{
95	struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
96
97	if (entry->hook == NF_INET_LOCAL_OUT) {
98		const struct iphdr *iph = ip_hdr(skb);
99
100		rt_info->tos = iph->tos;
101		rt_info->daddr = iph->daddr;
102		rt_info->saddr = iph->saddr;
103		rt_info->mark = skb->mark;
104	}
105}
106
107static int nf_ip_reroute(struct sk_buff *skb,
108			 const struct nf_queue_entry *entry)
109{
110	const struct ip_rt_info *rt_info = nf_queue_entry_reroute(entry);
111
112	if (entry->hook == NF_INET_LOCAL_OUT) {
113		const struct iphdr *iph = ip_hdr(skb);
114
115		if (!(iph->tos == rt_info->tos &&
116		      skb->mark == rt_info->mark &&
117		      iph->daddr == rt_info->daddr &&
118		      iph->saddr == rt_info->saddr))
119			return ip_route_me_harder(skb, RTN_UNSPEC);
120	}
121	return 0;
122}
123
124__sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
125			    unsigned int dataoff, u_int8_t protocol)
126{
127	const struct iphdr *iph = ip_hdr(skb);
128	__sum16 csum = 0;
129
130	switch (skb->ip_summed) {
131	case CHECKSUM_COMPLETE:
132		if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
133			break;
134		if ((protocol == 0 && !csum_fold(skb->csum)) ||
135		    !csum_tcpudp_magic(iph->saddr, iph->daddr,
136				       skb->len - dataoff, protocol,
137				       skb->csum)) {
138			skb->ip_summed = CHECKSUM_UNNECESSARY;
139			break;
140		}
141		/* fall through */
142	case CHECKSUM_NONE:
143		if (protocol == 0)
144			skb->csum = 0;
145		else
146			skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
147						       skb->len - dataoff,
148						       protocol, 0);
149		csum = __skb_checksum_complete(skb);
150	}
151	return csum;
152}
153EXPORT_SYMBOL(nf_ip_checksum);
154
155static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
156				      unsigned int dataoff, unsigned int len,
157				      u_int8_t protocol)
158{
159	const struct iphdr *iph = ip_hdr(skb);
160	__sum16 csum = 0;
161
162	switch (skb->ip_summed) {
163	case CHECKSUM_COMPLETE:
164		if (len == skb->len - dataoff)
165			return nf_ip_checksum(skb, hook, dataoff, protocol);
166		/* fall through */
167	case CHECKSUM_NONE:
168		skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr, protocol,
169					       skb->len - dataoff, 0);
170		skb->ip_summed = CHECKSUM_NONE;
171		return __skb_checksum_complete_head(skb, dataoff + len);
172	}
173	return csum;
174}
175
176static int nf_ip_route(struct net *net, struct dst_entry **dst,
177		       struct flowi *fl, bool strict __always_unused)
178{
179	struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
180	if (IS_ERR(rt))
181		return PTR_ERR(rt);
182	*dst = &rt->dst;
183	return 0;
184}
185
186static const struct nf_afinfo nf_ip_afinfo = {
187	.family			= AF_INET,
188	.checksum		= nf_ip_checksum,
189	.checksum_partial	= nf_ip_checksum_partial,
190	.route			= nf_ip_route,
191	.saveroute		= nf_ip_saveroute,
192	.reroute		= nf_ip_reroute,
193	.route_key_size		= sizeof(struct ip_rt_info),
194};
195
196static int __init ipv4_netfilter_init(void)
197{
198	return nf_register_afinfo(&nf_ip_afinfo);
199}
200
201static void __exit ipv4_netfilter_fini(void)
202{
203	nf_unregister_afinfo(&nf_ip_afinfo);
204}
205
206module_init(ipv4_netfilter_init);
207module_exit(ipv4_netfilter_fini);
208