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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 | * | |
f229f6ce PM |
24 | * (C) 2006-2012 Patrick McHardy <kaber@trash.net> |
25 | * | |
f09943fe PM |
26 | */ |
27 | ||
28 | #include <linux/module.h> | |
29 | #include <linux/skbuff.h> | |
30 | #include <linux/ip.h> | |
31 | ||
32 | #include <net/netfilter/nf_nat.h> | |
c7232c99 | 33 | #include <net/netfilter/nf_nat_l4proto.h> |
f09943fe PM |
34 | #include <linux/netfilter/nf_conntrack_proto_gre.h> |
35 | ||
36 | MODULE_LICENSE("GPL"); | |
37 | MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>"); | |
38 | MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE"); | |
39 | ||
f09943fe | 40 | /* generate unique tuple ... */ |
f43dc98b | 41 | static void |
c7232c99 PM |
42 | gre_unique_tuple(const struct nf_nat_l3proto *l3proto, |
43 | struct nf_conntrack_tuple *tuple, | |
44 | const struct nf_nat_range *range, | |
f09943fe | 45 | enum nf_nat_manip_type maniptype, |
c88130bc | 46 | const struct nf_conn *ct) |
f09943fe PM |
47 | { |
48 | static u_int16_t key; | |
49 | __be16 *keyptr; | |
50 | unsigned int min, i, range_size; | |
51 | ||
c2a1910b JB |
52 | /* If there is no master conntrack we are not PPTP, |
53 | do not change tuples */ | |
c88130bc | 54 | if (!ct->master) |
f43dc98b | 55 | return; |
c2a1910b | 56 | |
cbc9f2f4 | 57 | if (maniptype == NF_NAT_MANIP_SRC) |
f09943fe PM |
58 | keyptr = &tuple->src.u.gre.key; |
59 | else | |
60 | keyptr = &tuple->dst.u.gre.key; | |
61 | ||
cbc9f2f4 | 62 | if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) { |
c88130bc | 63 | pr_debug("%p: NATing GRE PPTP\n", ct); |
f09943fe PM |
64 | min = 1; |
65 | range_size = 0xffff; | |
66 | } else { | |
c7232c99 PM |
67 | min = ntohs(range->min_proto.gre.key); |
68 | range_size = ntohs(range->max_proto.gre.key) - min + 1; | |
f09943fe PM |
69 | } |
70 | ||
0d53778e | 71 | pr_debug("min = %u, range_size = %u\n", min, range_size); |
f09943fe | 72 | |
2452a99d | 73 | for (i = 0; ; ++key) { |
f09943fe | 74 | *keyptr = htons(min + key % range_size); |
2452a99d | 75 | if (++i == range_size || !nf_nat_used_tuple(tuple, ct)) |
f43dc98b | 76 | return; |
f09943fe PM |
77 | } |
78 | ||
c88130bc | 79 | pr_debug("%p: no NAT mapping\n", ct); |
f43dc98b | 80 | return; |
f09943fe PM |
81 | } |
82 | ||
83 | /* manipulate a GRE packet according to maniptype */ | |
f2ea825f | 84 | static bool |
c7232c99 PM |
85 | gre_manip_pkt(struct sk_buff *skb, |
86 | const struct nf_nat_l3proto *l3proto, | |
87 | unsigned int iphdroff, unsigned int hdroff, | |
f09943fe PM |
88 | const struct nf_conntrack_tuple *tuple, |
89 | enum nf_nat_manip_type maniptype) | |
90 | { | |
12c33aa2 | 91 | const struct gre_hdr *greh; |
f09943fe | 92 | struct gre_hdr_pptp *pgreh; |
f09943fe PM |
93 | |
94 | /* pgreh includes two optional 32bit fields which are not required | |
95 | * to be there. That's where the magic '8' comes from */ | |
3db05fea | 96 | if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8)) |
f2ea825f | 97 | return false; |
f09943fe | 98 | |
3db05fea | 99 | greh = (void *)skb->data + hdroff; |
f09943fe PM |
100 | pgreh = (struct gre_hdr_pptp *)greh; |
101 | ||
102 | /* we only have destination manip of a packet, since 'source key' | |
103 | * is not present in the packet itself */ | |
cbc9f2f4 | 104 | if (maniptype != NF_NAT_MANIP_DST) |
f2ea825f | 105 | return true; |
f09943fe | 106 | switch (greh->version) { |
c2a1910b JB |
107 | case GRE_VERSION_1701: |
108 | /* We do not currently NAT any GREv0 packets. | |
109 | * Try to behave like "nf_nat_proto_unknown" */ | |
f09943fe PM |
110 | break; |
111 | case GRE_VERSION_PPTP: | |
0d53778e | 112 | pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key)); |
f09943fe PM |
113 | pgreh->call_id = tuple->dst.u.gre.key; |
114 | break; | |
115 | default: | |
0d53778e | 116 | pr_debug("can't nat unknown GRE version\n"); |
f2ea825f | 117 | return false; |
f09943fe | 118 | } |
f2ea825f | 119 | return true; |
f09943fe PM |
120 | } |
121 | ||
c7232c99 PM |
122 | static const struct nf_nat_l4proto gre = { |
123 | .l4proto = IPPROTO_GRE, | |
f09943fe | 124 | .manip_pkt = gre_manip_pkt, |
c7232c99 | 125 | .in_range = nf_nat_l4proto_in_range, |
f09943fe | 126 | .unique_tuple = gre_unique_tuple, |
24de3d37 | 127 | #if IS_ENABLED(CONFIG_NF_CT_NETLINK) |
c7232c99 | 128 | .nlattr_to_range = nf_nat_l4proto_nlattr_to_range, |
f09943fe PM |
129 | #endif |
130 | }; | |
131 | ||
f4f6fb71 | 132 | static int __init nf_nat_proto_gre_init(void) |
f09943fe | 133 | { |
c7232c99 | 134 | return nf_nat_l4proto_register(NFPROTO_IPV4, &gre); |
f09943fe PM |
135 | } |
136 | ||
f4f6fb71 | 137 | static void __exit nf_nat_proto_gre_fini(void) |
f09943fe | 138 | { |
c7232c99 | 139 | nf_nat_l4proto_unregister(NFPROTO_IPV4, &gre); |
f09943fe PM |
140 | } |
141 | ||
142 | module_init(nf_nat_proto_gre_init); | |
143 | module_exit(nf_nat_proto_gre_fini); | |
144 | ||
145 | void nf_nat_need_gre(void) | |
146 | { | |
147 | return; | |
148 | } | |
149 | EXPORT_SYMBOL_GPL(nf_nat_need_gre); |