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f09943fe PM |
1 | /* |
2 | * nf_nat_proto_gre.c | |
3 | * | |
4 | * NAT protocol helper module for GRE. | |
5 | * | |
6 | * GRE is a generic encapsulation protocol, which is generally not very | |
7 | * suited for NAT, as it has no protocol-specific part as port numbers. | |
8 | * | |
9 | * It has an optional key field, which may help us distinguishing two | |
10 | * connections between the same two hosts. | |
11 | * | |
12 | * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784 | |
13 | * | |
14 | * PPTP is built on top of a modified version of GRE, and has a mandatory | |
15 | * field called "CallID", which serves us for the same purpose as the key | |
16 | * field in plain GRE. | |
17 | * | |
18 | * Documentation about PPTP can be found in RFC 2637 | |
19 | * | |
20 | * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org> | |
21 | * | |
22 | * Development of this code funded by Astaro AG (http://www.astaro.com/) | |
23 | * | |
24 | */ | |
25 | ||
26 | #include <linux/module.h> | |
27 | #include <linux/skbuff.h> | |
28 | #include <linux/ip.h> | |
29 | ||
30 | #include <net/netfilter/nf_nat.h> | |
31 | #include <net/netfilter/nf_nat_rule.h> | |
32 | #include <net/netfilter/nf_nat_protocol.h> | |
33 | #include <linux/netfilter/nf_conntrack_proto_gre.h> | |
34 | ||
35 | MODULE_LICENSE("GPL"); | |
36 | MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>"); | |
37 | MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE"); | |
38 | ||
f09943fe PM |
39 | /* is key in given range between min and max */ |
40 | static int | |
41 | gre_in_range(const struct nf_conntrack_tuple *tuple, | |
42 | enum nf_nat_manip_type maniptype, | |
43 | const union nf_conntrack_man_proto *min, | |
44 | const union nf_conntrack_man_proto *max) | |
45 | { | |
46 | __be16 key; | |
47 | ||
48 | if (maniptype == IP_NAT_MANIP_SRC) | |
49 | key = tuple->src.u.gre.key; | |
50 | else | |
51 | key = tuple->dst.u.gre.key; | |
52 | ||
53 | return ntohs(key) >= ntohs(min->gre.key) && | |
54 | ntohs(key) <= ntohs(max->gre.key); | |
55 | } | |
56 | ||
57 | /* generate unique tuple ... */ | |
58 | static int | |
59 | gre_unique_tuple(struct nf_conntrack_tuple *tuple, | |
60 | const struct nf_nat_range *range, | |
61 | enum nf_nat_manip_type maniptype, | |
62 | const struct nf_conn *conntrack) | |
63 | { | |
64 | static u_int16_t key; | |
65 | __be16 *keyptr; | |
66 | unsigned int min, i, range_size; | |
67 | ||
c2a1910b JB |
68 | /* If there is no master conntrack we are not PPTP, |
69 | do not change tuples */ | |
70 | if (!conntrack->master) | |
71 | return 0; | |
72 | ||
f09943fe PM |
73 | if (maniptype == IP_NAT_MANIP_SRC) |
74 | keyptr = &tuple->src.u.gre.key; | |
75 | else | |
76 | keyptr = &tuple->dst.u.gre.key; | |
77 | ||
78 | if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) { | |
0d53778e | 79 | pr_debug("%p: NATing GRE PPTP\n", conntrack); |
f09943fe PM |
80 | min = 1; |
81 | range_size = 0xffff; | |
82 | } else { | |
83 | min = ntohs(range->min.gre.key); | |
84 | range_size = ntohs(range->max.gre.key) - min + 1; | |
85 | } | |
86 | ||
0d53778e | 87 | pr_debug("min = %u, range_size = %u\n", min, range_size); |
f09943fe PM |
88 | |
89 | for (i = 0; i < range_size; i++, key++) { | |
90 | *keyptr = htons(min + key % range_size); | |
91 | if (!nf_nat_used_tuple(tuple, conntrack)) | |
92 | return 1; | |
93 | } | |
94 | ||
0d53778e | 95 | pr_debug("%p: no NAT mapping\n", conntrack); |
f09943fe PM |
96 | return 0; |
97 | } | |
98 | ||
99 | /* manipulate a GRE packet according to maniptype */ | |
100 | static int | |
101 | gre_manip_pkt(struct sk_buff **pskb, unsigned int iphdroff, | |
102 | const struct nf_conntrack_tuple *tuple, | |
103 | enum nf_nat_manip_type maniptype) | |
104 | { | |
105 | struct gre_hdr *greh; | |
106 | struct gre_hdr_pptp *pgreh; | |
107 | struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff); | |
108 | unsigned int hdroff = iphdroff + iph->ihl * 4; | |
109 | ||
110 | /* pgreh includes two optional 32bit fields which are not required | |
111 | * to be there. That's where the magic '8' comes from */ | |
37d41879 | 112 | if (!skb_make_writable(*pskb, hdroff + sizeof(*pgreh) - 8)) |
f09943fe PM |
113 | return 0; |
114 | ||
115 | greh = (void *)(*pskb)->data + hdroff; | |
116 | pgreh = (struct gre_hdr_pptp *)greh; | |
117 | ||
118 | /* we only have destination manip of a packet, since 'source key' | |
119 | * is not present in the packet itself */ | |
120 | if (maniptype != IP_NAT_MANIP_DST) | |
121 | return 1; | |
122 | switch (greh->version) { | |
c2a1910b JB |
123 | case GRE_VERSION_1701: |
124 | /* We do not currently NAT any GREv0 packets. | |
125 | * Try to behave like "nf_nat_proto_unknown" */ | |
f09943fe PM |
126 | break; |
127 | case GRE_VERSION_PPTP: | |
0d53778e | 128 | pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key)); |
f09943fe PM |
129 | pgreh->call_id = tuple->dst.u.gre.key; |
130 | break; | |
131 | default: | |
0d53778e | 132 | pr_debug("can't nat unknown GRE version\n"); |
f09943fe PM |
133 | return 0; |
134 | } | |
135 | return 1; | |
136 | } | |
137 | ||
138 | static struct nf_nat_protocol gre __read_mostly = { | |
139 | .name = "GRE", | |
140 | .protonum = IPPROTO_GRE, | |
141 | .manip_pkt = gre_manip_pkt, | |
142 | .in_range = gre_in_range, | |
143 | .unique_tuple = gre_unique_tuple, | |
e281db5c | 144 | #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE) |
fdf70832 PM |
145 | .range_to_nlattr = nf_nat_port_range_to_nlattr, |
146 | .nlattr_to_range = nf_nat_port_nlattr_to_range, | |
f09943fe PM |
147 | #endif |
148 | }; | |
149 | ||
150 | int __init nf_nat_proto_gre_init(void) | |
151 | { | |
152 | return nf_nat_protocol_register(&gre); | |
153 | } | |
154 | ||
155 | void __exit nf_nat_proto_gre_fini(void) | |
156 | { | |
157 | nf_nat_protocol_unregister(&gre); | |
158 | } | |
159 | ||
160 | module_init(nf_nat_proto_gre_init); | |
161 | module_exit(nf_nat_proto_gre_fini); | |
162 | ||
163 | void nf_nat_need_gre(void) | |
164 | { | |
165 | return; | |
166 | } | |
167 | EXPORT_SYMBOL_GPL(nf_nat_need_gre); |