151 lines
3.9 KiB
C
Executable File
151 lines
3.9 KiB
C
Executable File
/*
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* nf_nat_proto_gre.c
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*
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* NAT protocol helper module for GRE.
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*
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* GRE is a generic encapsulation protocol, which is generally not very
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* suited for NAT, as it has no protocol-specific part as port numbers.
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*
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* It has an optional key field, which may help us distinguishing two
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* connections between the same two hosts.
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*
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* GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
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*
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* PPTP is built on top of a modified version of GRE, and has a mandatory
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* field called "CallID", which serves us for the same purpose as the key
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* field in plain GRE.
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*
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* Documentation about PPTP can be found in RFC 2637
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*
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* (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
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*
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* Development of this code funded by Astaro AG (http://www.astaro.com/)
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*
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* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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*
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*/
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <net/netfilter/nf_nat.h>
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#include <net/netfilter/nf_nat_l4proto.h>
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#include <linux/netfilter/nf_conntrack_proto_gre.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
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MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
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/* generate unique tuple ... */
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static void
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gre_unique_tuple(const struct nf_nat_l3proto *l3proto,
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struct nf_conntrack_tuple *tuple,
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const struct nf_nat_range *range,
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enum nf_nat_manip_type maniptype,
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const struct nf_conn *ct)
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{
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static u_int16_t key;
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__be16 *keyptr;
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unsigned int min, i, range_size;
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/* If there is no master conntrack we are not PPTP,
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do not change tuples */
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if (!ct->master)
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return;
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if (maniptype == NF_NAT_MANIP_SRC)
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keyptr = &tuple->src.u.gre.key;
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else
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keyptr = &tuple->dst.u.gre.key;
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if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) {
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pr_debug("%p: NATing GRE PPTP\n", ct);
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min = 1;
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range_size = 0xffff;
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} else {
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min = ntohs(range->min_proto.gre.key);
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range_size = ntohs(range->max_proto.gre.key) - min + 1;
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}
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pr_debug("min = %u, range_size = %u\n", min, range_size);
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for (i = 0; ; ++key) {
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*keyptr = htons(min + key % range_size);
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if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
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return;
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}
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pr_debug("%p: no NAT mapping\n", ct);
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return;
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}
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/* manipulate a GRE packet according to maniptype */
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static bool
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gre_manip_pkt(struct sk_buff *skb,
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const struct nf_nat_l3proto *l3proto,
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unsigned int iphdroff, unsigned int hdroff,
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const struct nf_conntrack_tuple *tuple,
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enum nf_nat_manip_type maniptype)
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{
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const struct gre_base_hdr *greh;
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struct pptp_gre_header *pgreh;
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/* pgreh includes two optional 32bit fields which are not required
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* to be there. That's where the magic '8' comes from */
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if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
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return false;
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greh = (void *)skb->data + hdroff;
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pgreh = (struct pptp_gre_header *)greh;
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/* we only have destination manip of a packet, since 'source key'
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* is not present in the packet itself */
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if (maniptype != NF_NAT_MANIP_DST)
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return true;
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switch (greh->flags & GRE_VERSION) {
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case GRE_VERSION_0:
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/* We do not currently NAT any GREv0 packets.
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* Try to behave like "nf_nat_proto_unknown" */
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break;
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case GRE_VERSION_1:
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pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
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pgreh->call_id = tuple->dst.u.gre.key;
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break;
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default:
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pr_debug("can't nat unknown GRE version\n");
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return false;
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}
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return true;
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}
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static const struct nf_nat_l4proto gre = {
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.l4proto = IPPROTO_GRE,
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.manip_pkt = gre_manip_pkt,
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.in_range = nf_nat_l4proto_in_range,
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.unique_tuple = gre_unique_tuple,
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#if IS_ENABLED(CONFIG_NF_CT_NETLINK)
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.nlattr_to_range = nf_nat_l4proto_nlattr_to_range,
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#endif
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};
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static int __init nf_nat_proto_gre_init(void)
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{
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return nf_nat_l4proto_register(NFPROTO_IPV4, &gre);
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}
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static void __exit nf_nat_proto_gre_fini(void)
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{
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nf_nat_l4proto_unregister(NFPROTO_IPV4, &gre);
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}
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module_init(nf_nat_proto_gre_init);
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module_exit(nf_nat_proto_gre_fini);
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void nf_nat_need_gre(void)
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{
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return;
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}
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EXPORT_SYMBOL_GPL(nf_nat_need_gre);
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