| 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_l4proto.h> |
| 32 | #include <linux/netfilter/nf_conntrack_proto_gre.h> |
| 33 | |
| 34 | MODULE_LICENSE("GPL"); |
| 35 | MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>"); |
| 36 | MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE"); |
| 37 | |
| 38 | /* generate unique tuple ... */ |
| 39 | static void |
| 40 | gre_unique_tuple(const struct nf_nat_l3proto *l3proto, |
| 41 | struct nf_conntrack_tuple *tuple, |
| 42 | const struct nf_nat_range *range, |
| 43 | enum nf_nat_manip_type maniptype, |
| 44 | const struct nf_conn *ct) |
| 45 | { |
| 46 | static u_int16_t key; |
| 47 | __be16 *keyptr; |
| 48 | unsigned int min, i, range_size; |
| 49 | |
| 50 | /* If there is no master conntrack we are not PPTP, |
| 51 | do not change tuples */ |
| 52 | if (!ct->master) |
| 53 | return; |
| 54 | |
| 55 | if (maniptype == NF_NAT_MANIP_SRC) |
| 56 | keyptr = &tuple->src.u.gre.key; |
| 57 | else |
| 58 | keyptr = &tuple->dst.u.gre.key; |
| 59 | |
| 60 | if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) { |
| 61 | pr_debug("%p: NATing GRE PPTP\n", ct); |
| 62 | min = 1; |
| 63 | range_size = 0xffff; |
| 64 | } else { |
| 65 | min = ntohs(range->min_proto.gre.key); |
| 66 | range_size = ntohs(range->max_proto.gre.key) - min + 1; |
| 67 | } |
| 68 | |
| 69 | pr_debug("min = %u, range_size = %u\n", min, range_size); |
| 70 | |
| 71 | for (i = 0; ; ++key) { |
| 72 | *keyptr = htons(min + key % range_size); |
| 73 | if (++i == range_size || !nf_nat_used_tuple(tuple, ct)) |
| 74 | return; |
| 75 | } |
| 76 | |
| 77 | pr_debug("%p: no NAT mapping\n", ct); |
| 78 | return; |
| 79 | } |
| 80 | |
| 81 | /* manipulate a GRE packet according to maniptype */ |
| 82 | static bool |
| 83 | gre_manip_pkt(struct sk_buff *skb, |
| 84 | const struct nf_nat_l3proto *l3proto, |
| 85 | unsigned int iphdroff, unsigned int hdroff, |
| 86 | const struct nf_conntrack_tuple *tuple, |
| 87 | enum nf_nat_manip_type maniptype) |
| 88 | { |
| 89 | const struct gre_hdr *greh; |
| 90 | struct gre_hdr_pptp *pgreh; |
| 91 | |
| 92 | /* pgreh includes two optional 32bit fields which are not required |
| 93 | * to be there. That's where the magic '8' comes from */ |
| 94 | if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8)) |
| 95 | return false; |
| 96 | |
| 97 | greh = (void *)skb->data + hdroff; |
| 98 | pgreh = (struct gre_hdr_pptp *)greh; |
| 99 | |
| 100 | /* we only have destination manip of a packet, since 'source key' |
| 101 | * is not present in the packet itself */ |
| 102 | if (maniptype != NF_NAT_MANIP_DST) |
| 103 | return true; |
| 104 | switch (greh->version) { |
| 105 | case GRE_VERSION_1701: |
| 106 | /* We do not currently NAT any GREv0 packets. |
| 107 | * Try to behave like "nf_nat_proto_unknown" */ |
| 108 | break; |
| 109 | case GRE_VERSION_PPTP: |
| 110 | pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key)); |
| 111 | pgreh->call_id = tuple->dst.u.gre.key; |
| 112 | break; |
| 113 | default: |
| 114 | pr_debug("can't nat unknown GRE version\n"); |
| 115 | return false; |
| 116 | } |
| 117 | return true; |
| 118 | } |
| 119 | |
| 120 | static const struct nf_nat_l4proto gre = { |
| 121 | .l4proto = IPPROTO_GRE, |
| 122 | .manip_pkt = gre_manip_pkt, |
| 123 | .in_range = nf_nat_l4proto_in_range, |
| 124 | .unique_tuple = gre_unique_tuple, |
| 125 | #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE) |
| 126 | .nlattr_to_range = nf_nat_l4proto_nlattr_to_range, |
| 127 | #endif |
| 128 | }; |
| 129 | |
| 130 | static int __init nf_nat_proto_gre_init(void) |
| 131 | { |
| 132 | return nf_nat_l4proto_register(NFPROTO_IPV4, &gre); |
| 133 | } |
| 134 | |
| 135 | static void __exit nf_nat_proto_gre_fini(void) |
| 136 | { |
| 137 | nf_nat_l4proto_unregister(NFPROTO_IPV4, &gre); |
| 138 | } |
| 139 | |
| 140 | module_init(nf_nat_proto_gre_init); |
| 141 | module_exit(nf_nat_proto_gre_fini); |
| 142 | |
| 143 | void nf_nat_need_gre(void) |
| 144 | { |
| 145 | return; |
| 146 | } |
| 147 | EXPORT_SYMBOL_GPL(nf_nat_need_gre); |