1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2011, 2012 Patrick McHardy <kaber@trash.net>
4 */
5
6 #include <linux/module.h>
7 #include <linux/skbuff.h>
8 #include <linux/ipv6.h>
9 #include <net/ipv6.h>
10 #include <linux/netfilter.h>
11 #include <linux/netfilter_ipv6.h>
12 #include <linux/netfilter_ipv6/ip6t_NPT.h>
13 #include <linux/netfilter/x_tables.h>
14
ip6t_npt_checkentry(const struct xt_tgchk_param * par)15 static int ip6t_npt_checkentry(const struct xt_tgchk_param *par)
16 {
17 struct ip6t_npt_tginfo *npt = par->targinfo;
18 struct in6_addr pfx;
19 __wsum src_sum, dst_sum;
20
21 if (npt->src_pfx_len > 64 || npt->dst_pfx_len > 64)
22 return -EINVAL;
23
24 /* Ensure that LSB of prefix is zero */
25 ipv6_addr_prefix(&pfx, &npt->src_pfx.in6, npt->src_pfx_len);
26 if (!ipv6_addr_equal(&pfx, &npt->src_pfx.in6))
27 return -EINVAL;
28 ipv6_addr_prefix(&pfx, &npt->dst_pfx.in6, npt->dst_pfx_len);
29 if (!ipv6_addr_equal(&pfx, &npt->dst_pfx.in6))
30 return -EINVAL;
31
32 src_sum = csum_partial(&npt->src_pfx.in6, sizeof(npt->src_pfx.in6), 0);
33 dst_sum = csum_partial(&npt->dst_pfx.in6, sizeof(npt->dst_pfx.in6), 0);
34
35 npt->adjustment = ~csum_fold(csum_sub(src_sum, dst_sum));
36 return 0;
37 }
38
ip6t_npt_map_pfx(const struct ip6t_npt_tginfo * npt,struct in6_addr * addr)39 static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
40 struct in6_addr *addr)
41 {
42 unsigned int pfx_len;
43 unsigned int i, idx;
44 __be32 mask;
45 __sum16 sum;
46
47 pfx_len = max(npt->src_pfx_len, npt->dst_pfx_len);
48 for (i = 0; i < pfx_len; i += 32) {
49 if (pfx_len - i >= 32)
50 mask = 0;
51 else
52 mask = htonl((1 << (i - pfx_len + 32)) - 1);
53
54 idx = i / 32;
55 addr->s6_addr32[idx] &= mask;
56 addr->s6_addr32[idx] |= ~mask & npt->dst_pfx.in6.s6_addr32[idx];
57 }
58
59 if (pfx_len <= 48)
60 idx = 3;
61 else {
62 for (idx = 4; idx < ARRAY_SIZE(addr->s6_addr16); idx++) {
63 if ((__force __sum16)addr->s6_addr16[idx] !=
64 CSUM_MANGLED_0)
65 break;
66 }
67 if (idx == ARRAY_SIZE(addr->s6_addr16))
68 return false;
69 }
70
71 sum = ~csum_fold(csum_add(csum_unfold((__force __sum16)addr->s6_addr16[idx]),
72 csum_unfold(npt->adjustment)));
73 if (sum == CSUM_MANGLED_0)
74 sum = 0;
75 *(__force __sum16 *)&addr->s6_addr16[idx] = sum;
76
77 return true;
78 }
79
icmpv6_bounced_ipv6hdr(struct sk_buff * skb,struct ipv6hdr * _bounced_hdr)80 static struct ipv6hdr *icmpv6_bounced_ipv6hdr(struct sk_buff *skb,
81 struct ipv6hdr *_bounced_hdr)
82 {
83 if (ipv6_hdr(skb)->nexthdr != IPPROTO_ICMPV6)
84 return NULL;
85
86 if (!icmpv6_is_err(icmp6_hdr(skb)->icmp6_type))
87 return NULL;
88
89 return skb_header_pointer(skb,
90 skb_transport_offset(skb) + sizeof(struct icmp6hdr),
91 sizeof(struct ipv6hdr),
92 _bounced_hdr);
93 }
94
95 static unsigned int
ip6t_snpt_tg(struct sk_buff * skb,const struct xt_action_param * par)96 ip6t_snpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
97 {
98 const struct ip6t_npt_tginfo *npt = par->targinfo;
99 struct ipv6hdr _bounced_hdr;
100 struct ipv6hdr *bounced_hdr;
101 struct in6_addr bounced_pfx;
102
103 if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->saddr)) {
104 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
105 offsetof(struct ipv6hdr, saddr));
106 return NF_DROP;
107 }
108
109 /* rewrite dst addr of bounced packet which was sent to dst range */
110 bounced_hdr = icmpv6_bounced_ipv6hdr(skb, &_bounced_hdr);
111 if (bounced_hdr) {
112 ipv6_addr_prefix(&bounced_pfx, &bounced_hdr->daddr, npt->src_pfx_len);
113 if (ipv6_addr_cmp(&bounced_pfx, &npt->src_pfx.in6) == 0)
114 ip6t_npt_map_pfx(npt, &bounced_hdr->daddr);
115 }
116
117 return XT_CONTINUE;
118 }
119
120 static unsigned int
ip6t_dnpt_tg(struct sk_buff * skb,const struct xt_action_param * par)121 ip6t_dnpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
122 {
123 const struct ip6t_npt_tginfo *npt = par->targinfo;
124 struct ipv6hdr _bounced_hdr;
125 struct ipv6hdr *bounced_hdr;
126 struct in6_addr bounced_pfx;
127
128 if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->daddr)) {
129 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
130 offsetof(struct ipv6hdr, daddr));
131 return NF_DROP;
132 }
133
134 /* rewrite src addr of bounced packet which was sent from dst range */
135 bounced_hdr = icmpv6_bounced_ipv6hdr(skb, &_bounced_hdr);
136 if (bounced_hdr) {
137 ipv6_addr_prefix(&bounced_pfx, &bounced_hdr->saddr, npt->src_pfx_len);
138 if (ipv6_addr_cmp(&bounced_pfx, &npt->src_pfx.in6) == 0)
139 ip6t_npt_map_pfx(npt, &bounced_hdr->saddr);
140 }
141
142 return XT_CONTINUE;
143 }
144
145 static struct xt_target ip6t_npt_target_reg[] __read_mostly = {
146 {
147 .name = "SNPT",
148 .table = "mangle",
149 .target = ip6t_snpt_tg,
150 .targetsize = sizeof(struct ip6t_npt_tginfo),
151 .usersize = offsetof(struct ip6t_npt_tginfo, adjustment),
152 .checkentry = ip6t_npt_checkentry,
153 .family = NFPROTO_IPV6,
154 .hooks = (1 << NF_INET_LOCAL_IN) |
155 (1 << NF_INET_POST_ROUTING),
156 .me = THIS_MODULE,
157 },
158 {
159 .name = "DNPT",
160 .table = "mangle",
161 .target = ip6t_dnpt_tg,
162 .targetsize = sizeof(struct ip6t_npt_tginfo),
163 .usersize = offsetof(struct ip6t_npt_tginfo, adjustment),
164 .checkentry = ip6t_npt_checkentry,
165 .family = NFPROTO_IPV6,
166 .hooks = (1 << NF_INET_PRE_ROUTING) |
167 (1 << NF_INET_LOCAL_OUT),
168 .me = THIS_MODULE,
169 },
170 };
171
ip6t_npt_init(void)172 static int __init ip6t_npt_init(void)
173 {
174 return xt_register_targets(ip6t_npt_target_reg,
175 ARRAY_SIZE(ip6t_npt_target_reg));
176 }
177
ip6t_npt_exit(void)178 static void __exit ip6t_npt_exit(void)
179 {
180 xt_unregister_targets(ip6t_npt_target_reg,
181 ARRAY_SIZE(ip6t_npt_target_reg));
182 }
183
184 module_init(ip6t_npt_init);
185 module_exit(ip6t_npt_exit);
186
187 MODULE_LICENSE("GPL");
188 MODULE_DESCRIPTION("IPv6-to-IPv6 Network Prefix Translation (RFC 6296)");
189 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
190 MODULE_ALIAS("ip6t_SNPT");
191 MODULE_ALIAS("ip6t_DNPT");
192