LXR linux/net/ipv4/netfilter/nf_nat

   1/*
   2 * nf_nat_pptp.c
   3 *
   4 * NAT support for PPTP (Point to Point Tunneling Protocol).
   5 * PPTP is a a protocol for creating virtual private networks.
   6 * It is a specification defined by Microsoft and some vendors
   7 * working with Microsoft.  PPTP is built on top of a modified
   8 * version of the Internet Generic Routing Encapsulation Protocol.
   9 * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
  10 * PPTP can be found in RFC 2637
  11 *
  12 * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  13 *
  14 * Development of this code funded by Astaro AG (http://www.astaro.com/)
  15 *
  16 * TODO: - NAT to a unique tuple, not to TCP source port
  17 *         (needs netfilter tuple reservation)
  18 */
  19
  20#include <linux/module.h>
  21#include <linux/tcp.h>
  22
  23#include <net/netfilter/nf_nat.h>
  24#include <net/netfilter/nf_nat_helper.h>
  25#include <net/netfilter/nf_nat_rule.h>
  26#include <net/netfilter/nf_conntrack_helper.h>
  27#include <net/netfilter/nf_conntrack_expect.h>
  28#include <linux/netfilter/nf_conntrack_proto_gre.h>
  29#include <linux/netfilter/nf_conntrack_pptp.h>
  30
  31#define NF_NAT_PPTP_VERSION "3.0"
  32
  33#define REQ_CID(req, off)               (*(__be16 *)((char *)(req) + (off)))
  34
  35MODULE_LICENSE("GPL");
  36MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  37MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  38MODULE_ALIAS("ip_nat_pptp");
  39
  40static void pptp_nat_expected(struct nf_conn *ct,
  41                              struct nf_conntrack_expect *exp)
  42{
  43        struct net *net = nf_ct_net(ct);
  44        const struct nf_conn *master = ct->master;
  45        struct nf_conntrack_expect *other_exp;
  46        struct nf_conntrack_tuple t;
  47        const struct nf_ct_pptp_master *ct_pptp_info;
  48        const struct nf_nat_pptp *nat_pptp_info;
  49        struct nf_nat_range range;
  50
  51        ct_pptp_info = &nfct_help(master)->help.ct_pptp_info;
  52        nat_pptp_info = &nfct_nat(master)->help.nat_pptp_info;
  53
  54        /* And here goes the grand finale of corrosion... */
  55        if (exp->dir == IP_CT_DIR_ORIGINAL) {
  56                pr_debug("we are PNS->PAC\n");
  57                /* therefore, build tuple for PAC->PNS */
  58                t.src.l3num = AF_INET;
  59                t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  60                t.src.u.gre.key = ct_pptp_info->pac_call_id;
  61                t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  62                t.dst.u.gre.key = ct_pptp_info->pns_call_id;
  63                t.dst.protonum = IPPROTO_GRE;
  64        } else {
  65                pr_debug("we are PAC->PNS\n");
  66                /* build tuple for PNS->PAC */
  67                t.src.l3num = AF_INET;
  68                t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  69                t.src.u.gre.key = nat_pptp_info->pns_call_id;
  70                t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  71                t.dst.u.gre.key = nat_pptp_info->pac_call_id;
  72                t.dst.protonum = IPPROTO_GRE;
  73        }
  74
  75        pr_debug("trying to unexpect other dir: ");
  76        nf_ct_dump_tuple_ip(&t);
  77        other_exp = nf_ct_expect_find_get(net, &t);
  78        if (other_exp) {
  79                nf_ct_unexpect_related(other_exp);
  80                nf_ct_expect_put(other_exp);
  81                pr_debug("success\n");
  82        } else {
  83                pr_debug("not found!\n");
  84        }
  85
  86        /* This must be a fresh one. */
  87        BUG_ON(ct->status & IPS_NAT_DONE_MASK);
  88
  89        /* Change src to where master sends to */
  90        range.flags = IP_NAT_RANGE_MAP_IPS;
  91        range.min_ip = range.max_ip
  92                = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  93        if (exp->dir == IP_CT_DIR_ORIGINAL) {
  94                range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
  95                range.min = range.max = exp->saved_proto;
  96        }
  97        nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
  98
  99        /* For DST manip, map port here to where it's expected. */
 100        range.flags = IP_NAT_RANGE_MAP_IPS;
 101        range.min_ip = range.max_ip
 102                = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 103        if (exp->dir == IP_CT_DIR_REPLY) {
 104                range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 105                range.min = range.max = exp->saved_proto;
 106        }
 107        nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 108}
 109
 110/* outbound packets == from PNS to PAC */
 111static int
 112pptp_outbound_pkt(struct sk_buff *skb,
 113                  struct nf_conn *ct,
 114                  enum ip_conntrack_info ctinfo,
 115                  struct PptpControlHeader *ctlh,
 116                  union pptp_ctrl_union *pptpReq)
 117
 118{
 119        struct nf_ct_pptp_master *ct_pptp_info;
 120        struct nf_nat_pptp *nat_pptp_info;
 121        u_int16_t msg;
 122        __be16 new_callid;
 123        unsigned int cid_off;
 124
 125        ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 126        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 127
 128        new_callid = ct_pptp_info->pns_call_id;
 129
 130        switch (msg = ntohs(ctlh->messageType)) {
 131        case PPTP_OUT_CALL_REQUEST:
 132                cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 133                /* FIXME: ideally we would want to reserve a call ID
 134                 * here.  current netfilter NAT core is not able to do
 135                 * this :( For now we use TCP source port. This breaks
 136                 * multiple calls within one control session */
 137
 138                /* save original call ID in nat_info */
 139                nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 140
 141                /* don't use tcph->source since we are at a DSTmanip
 142                 * hook (e.g. PREROUTING) and pkt is not mangled yet */
 143                new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 144
 145                /* save new call ID in ct info */
 146                ct_pptp_info->pns_call_id = new_callid;
 147                break;
 148        case PPTP_IN_CALL_REPLY:
 149                cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 150                break;
 151        case PPTP_CALL_CLEAR_REQUEST:
 152                cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 153                break;
 154        default:
 155                pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
 156                         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 157                                               pptp_msg_name[0]);
 158                /* fall through */
 159        case PPTP_SET_LINK_INFO:
 160                /* only need to NAT in case PAC is behind NAT box */
 161        case PPTP_START_SESSION_REQUEST:
 162        case PPTP_START_SESSION_REPLY:
 163        case PPTP_STOP_SESSION_REQUEST:
 164        case PPTP_STOP_SESSION_REPLY:
 165        case PPTP_ECHO_REQUEST:
 166        case PPTP_ECHO_REPLY:
 167                /* no need to alter packet */
 168                return NF_ACCEPT;
 169        }
 170
 171        /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 172         * down to here */
 173        pr_debug("altering call id from 0x%04x to 0x%04x\n",
 174                 ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 175
 176        /* mangle packet */
 177        if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
 178                                     cid_off + sizeof(struct pptp_pkt_hdr) +
 179                                     sizeof(struct PptpControlHeader),
 180                                     sizeof(new_callid), (char *)&new_callid,
 181                                     sizeof(new_callid)) == 0)
 182                return NF_DROP;
 183        return NF_ACCEPT;
 184}
 185
 186static void
 187pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 188             struct nf_conntrack_expect *expect_reply)
 189{
 190        const struct nf_conn *ct = expect_orig->master;
 191        struct nf_ct_pptp_master *ct_pptp_info;
 192        struct nf_nat_pptp *nat_pptp_info;
 193
 194        ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 195        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 196
 197        /* save original PAC call ID in nat_info */
 198        nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 199
 200        /* alter expectation for PNS->PAC direction */
 201        expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 202        expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 203        expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 204        expect_orig->dir = IP_CT_DIR_ORIGINAL;
 205
 206        /* alter expectation for PAC->PNS direction */
 207        expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 208        expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 209        expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 210        expect_reply->dir = IP_CT_DIR_REPLY;
 211}
 212
 213/* inbound packets == from PAC to PNS */
 214static int
 215pptp_inbound_pkt(struct sk_buff *skb,
 216                 struct nf_conn *ct,
 217                 enum ip_conntrack_info ctinfo,
 218                 struct PptpControlHeader *ctlh,
 219                 union pptp_ctrl_union *pptpReq)
 220{
 221        const struct nf_nat_pptp *nat_pptp_info;
 222        u_int16_t msg;
 223        __be16 new_pcid;
 224        unsigned int pcid_off;
 225
 226        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 227        new_pcid = nat_pptp_info->pns_call_id;
 228
 229        switch (msg = ntohs(ctlh->messageType)) {
 230        case PPTP_OUT_CALL_REPLY:
 231                pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 232                break;
 233        case PPTP_IN_CALL_CONNECT:
 234                pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 235                break;
 236        case PPTP_IN_CALL_REQUEST:
 237                /* only need to nat in case PAC is behind NAT box */
 238                return NF_ACCEPT;
 239        case PPTP_WAN_ERROR_NOTIFY:
 240                pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 241                break;
 242        case PPTP_CALL_DISCONNECT_NOTIFY:
 243                pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 244                break;
 245        case PPTP_SET_LINK_INFO:
 246                pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 247                break;
 248        default:
 249                pr_debug("unknown inbound packet %s\n",
 250                         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 251                                               pptp_msg_name[0]);
 252                /* fall through */
 253        case PPTP_START_SESSION_REQUEST:
 254        case PPTP_START_SESSION_REPLY:
 255        case PPTP_STOP_SESSION_REQUEST:
 256        case PPTP_STOP_SESSION_REPLY:
 257        case PPTP_ECHO_REQUEST:
 258        case PPTP_ECHO_REPLY:
 259                /* no need to alter packet */
 260                return NF_ACCEPT;
 261        }
 262
 263        /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 264         * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 265
 266        /* mangle packet */
 267        pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
 268                 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 269
 270        if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
 271                                     pcid_off + sizeof(struct pptp_pkt_hdr) +
 272                                     sizeof(struct PptpControlHeader),
 273                                     sizeof(new_pcid), (char *)&new_pcid,
 274                                     sizeof(new_pcid)) == 0)
 275                return NF_DROP;
 276        return NF_ACCEPT;
 277}
 278
 279static int __init nf_nat_helper_pptp_init(void)
 280{
 281        nf_nat_need_gre();
 282
 283        BUG_ON(nf_nat_pptp_hook_outbound != NULL);
 284        rcu_assign_pointer(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 285
 286        BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 287        rcu_assign_pointer(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 288
 289        BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 290        rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 291
 292        BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 293        rcu_assign_pointer(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 294        return 0;
 295}
 296
 297static void __exit nf_nat_helper_pptp_fini(void)
 298{
 299        rcu_assign_pointer(nf_nat_pptp_hook_expectfn, NULL);
 300        rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, NULL);
 301        rcu_assign_pointer(nf_nat_pptp_hook_inbound, NULL);
 302        rcu_assign_pointer(nf_nat_pptp_hook_outbound, NULL);
 303        synchronize_rcu();
 304}
 305
 306module_init(nf_nat_helper_pptp_init);
 307module_exit(nf_nat_helper_pptp_fini);
 308