// SPDX-License-Identifier: GPL-2.0-only
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/*
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* nf_nat_pptp.c
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*
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* NAT support for PPTP (Point to Point Tunneling Protocol).
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* PPTP is a protocol for creating virtual private networks.
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* It is a specification defined by Microsoft and some vendors
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* working with Microsoft. PPTP is built on top of a modified
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* version of the Internet Generic Routing Encapsulation Protocol.
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* GRE is defined in RFC 1701 and RFC 1702. Documentation of
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* 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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* TODO: - NAT to a unique tuple, not to TCP source port
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* (needs netfilter tuple reservation)
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*/
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#include <linux/module.h>
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#include <linux/tcp.h>
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#include <net/netfilter/nf_nat.h>
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#include <net/netfilter/nf_nat_helper.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <net/netfilter/nf_conntrack_zones.h>
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#include <linux/netfilter/nf_conntrack_proto_gre.h>
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#include <linux/netfilter/nf_conntrack_pptp.h>
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#define NF_NAT_PPTP_VERSION "3.0"
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#define REQ_CID(req, off) (*(__be16 *)((char *)(req) + (off)))
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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 helper module for PPTP");
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MODULE_ALIAS_NF_NAT_HELPER("pptp");
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static void pptp_nat_expected(struct nf_conn *ct,
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struct nf_conntrack_expect *exp)
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{
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struct net *net = nf_ct_net(ct);
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const struct nf_conn *master = ct->master;
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struct nf_conntrack_expect *other_exp;
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struct nf_conntrack_tuple t = {};
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const struct nf_ct_pptp_master *ct_pptp_info;
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const struct nf_nat_pptp *nat_pptp_info;
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struct nf_nat_range2 range;
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struct nf_conn_nat *nat;
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nat = nf_ct_nat_ext_add(ct);
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if (WARN_ON_ONCE(!nat))
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return;
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nat_pptp_info = &nat->help.nat_pptp_info;
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ct_pptp_info = nfct_help_data(master);
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/* And here goes the grand finale of corrosion... */
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if (exp->dir == IP_CT_DIR_ORIGINAL) {
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pr_debug("we are PNS->PAC\n");
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/* therefore, build tuple for PAC->PNS */
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t.src.l3num = AF_INET;
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t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
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t.src.u.gre.key = ct_pptp_info->pac_call_id;
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t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
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t.dst.u.gre.key = ct_pptp_info->pns_call_id;
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t.dst.protonum = IPPROTO_GRE;
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} else {
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pr_debug("we are PAC->PNS\n");
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/* build tuple for PNS->PAC */
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t.src.l3num = AF_INET;
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t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
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t.src.u.gre.key = nat_pptp_info->pns_call_id;
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t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
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t.dst.u.gre.key = nat_pptp_info->pac_call_id;
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t.dst.protonum = IPPROTO_GRE;
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}
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pr_debug("trying to unexpect other dir: ");
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nf_ct_dump_tuple_ip(&t);
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other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
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if (other_exp) {
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nf_ct_unexpect_related(other_exp);
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nf_ct_expect_put(other_exp);
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pr_debug("success\n");
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} else {
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pr_debug("not found!\n");
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}
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/* This must be a fresh one. */
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BUG_ON(ct->status & IPS_NAT_DONE_MASK);
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/* Change src to where master sends to */
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range.flags = NF_NAT_RANGE_MAP_IPS;
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range.min_addr = range.max_addr
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= ct->master->tuplehash[!exp->dir].tuple.dst.u3;
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if (exp->dir == IP_CT_DIR_ORIGINAL) {
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range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
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range.min_proto = range.max_proto = exp->saved_proto;
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}
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nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
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/* For DST manip, map port here to where it's expected. */
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range.flags = NF_NAT_RANGE_MAP_IPS;
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range.min_addr = range.max_addr
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= ct->master->tuplehash[!exp->dir].tuple.src.u3;
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if (exp->dir == IP_CT_DIR_REPLY) {
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range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
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range.min_proto = range.max_proto = exp->saved_proto;
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}
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nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
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}
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/* outbound packets == from PNS to PAC */
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static int
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pptp_outbound_pkt(struct sk_buff *skb,
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struct nf_conn *ct,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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struct PptpControlHeader *ctlh,
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union pptp_ctrl_union *pptpReq)
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{
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struct nf_ct_pptp_master *ct_pptp_info;
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struct nf_conn_nat *nat = nfct_nat(ct);
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struct nf_nat_pptp *nat_pptp_info;
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u_int16_t msg;
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__be16 new_callid;
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unsigned int cid_off;
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if (WARN_ON_ONCE(!nat))
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return NF_DROP;
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nat_pptp_info = &nat->help.nat_pptp_info;
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ct_pptp_info = nfct_help_data(ct);
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new_callid = ct_pptp_info->pns_call_id;
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switch (msg = ntohs(ctlh->messageType)) {
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case PPTP_OUT_CALL_REQUEST:
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cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
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/* FIXME: ideally we would want to reserve a call ID
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* here. current netfilter NAT core is not able to do
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* this :( For now we use TCP source port. This breaks
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* multiple calls within one control session */
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/* save original call ID in nat_info */
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nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
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/* don't use tcph->source since we are at a DSTmanip
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* hook (e.g. PREROUTING) and pkt is not mangled yet */
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new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
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/* save new call ID in ct info */
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ct_pptp_info->pns_call_id = new_callid;
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break;
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case PPTP_IN_CALL_REPLY:
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cid_off = offsetof(union pptp_ctrl_union, icack.callID);
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break;
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case PPTP_CALL_CLEAR_REQUEST:
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cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
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break;
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default:
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pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
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pptp_msg_name(msg));
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fallthrough;
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case PPTP_SET_LINK_INFO:
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/* only need to NAT in case PAC is behind NAT box */
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case PPTP_START_SESSION_REQUEST:
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case PPTP_START_SESSION_REPLY:
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case PPTP_STOP_SESSION_REQUEST:
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case PPTP_STOP_SESSION_REPLY:
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case PPTP_ECHO_REQUEST:
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case PPTP_ECHO_REPLY:
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/* no need to alter packet */
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return NF_ACCEPT;
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}
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/* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
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* down to here */
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pr_debug("altering call id from 0x%04x to 0x%04x\n",
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ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
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/* mangle packet */
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if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
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cid_off + sizeof(struct pptp_pkt_hdr) +
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sizeof(struct PptpControlHeader),
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sizeof(new_callid), (char *)&new_callid,
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sizeof(new_callid)))
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return NF_DROP;
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return NF_ACCEPT;
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}
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static void
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pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
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struct nf_conntrack_expect *expect_reply)
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{
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const struct nf_conn *ct = expect_orig->master;
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struct nf_conn_nat *nat = nfct_nat(ct);
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struct nf_ct_pptp_master *ct_pptp_info;
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struct nf_nat_pptp *nat_pptp_info;
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if (WARN_ON_ONCE(!nat))
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return;
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nat_pptp_info = &nat->help.nat_pptp_info;
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ct_pptp_info = nfct_help_data(ct);
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/* save original PAC call ID in nat_info */
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nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
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/* alter expectation for PNS->PAC direction */
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expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
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expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
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expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
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expect_orig->dir = IP_CT_DIR_ORIGINAL;
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/* alter expectation for PAC->PNS direction */
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expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
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expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
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expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
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expect_reply->dir = IP_CT_DIR_REPLY;
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}
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/* inbound packets == from PAC to PNS */
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static int
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pptp_inbound_pkt(struct sk_buff *skb,
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struct nf_conn *ct,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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struct PptpControlHeader *ctlh,
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union pptp_ctrl_union *pptpReq)
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{
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const struct nf_nat_pptp *nat_pptp_info;
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struct nf_conn_nat *nat = nfct_nat(ct);
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u_int16_t msg;
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__be16 new_pcid;
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unsigned int pcid_off;
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if (WARN_ON_ONCE(!nat))
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return NF_DROP;
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nat_pptp_info = &nat->help.nat_pptp_info;
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new_pcid = nat_pptp_info->pns_call_id;
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switch (msg = ntohs(ctlh->messageType)) {
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case PPTP_OUT_CALL_REPLY:
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pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
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break;
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case PPTP_IN_CALL_CONNECT:
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pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
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break;
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case PPTP_IN_CALL_REQUEST:
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/* only need to nat in case PAC is behind NAT box */
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return NF_ACCEPT;
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case PPTP_WAN_ERROR_NOTIFY:
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pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
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break;
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case PPTP_CALL_DISCONNECT_NOTIFY:
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pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
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break;
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case PPTP_SET_LINK_INFO:
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pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
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break;
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default:
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pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
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fallthrough;
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case PPTP_START_SESSION_REQUEST:
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case PPTP_START_SESSION_REPLY:
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case PPTP_STOP_SESSION_REQUEST:
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case PPTP_STOP_SESSION_REPLY:
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case PPTP_ECHO_REQUEST:
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case PPTP_ECHO_REPLY:
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/* no need to alter packet */
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return NF_ACCEPT;
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}
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/* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
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* WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
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/* mangle packet */
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pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
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ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
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if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
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pcid_off + sizeof(struct pptp_pkt_hdr) +
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sizeof(struct PptpControlHeader),
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sizeof(new_pcid), (char *)&new_pcid,
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sizeof(new_pcid)))
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return NF_DROP;
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return NF_ACCEPT;
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}
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static int __init nf_nat_helper_pptp_init(void)
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{
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BUG_ON(nf_nat_pptp_hook_outbound != NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
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BUG_ON(nf_nat_pptp_hook_inbound != NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
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BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
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BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
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return 0;
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}
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static void __exit nf_nat_helper_pptp_fini(void)
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{
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RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, NULL);
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RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, NULL);
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synchronize_rcu();
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}
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module_init(nf_nat_helper_pptp_init);
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module_exit(nf_nat_helper_pptp_fini);
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