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 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  17 *
  18 * TODO: - NAT to a unique tuple, not to TCP source port
  19 *         (needs netfilter tuple reservation)
  20 */
  21
  22#include <linux/module.h>
  23#include <linux/tcp.h>
  24
  25#include <net/netfilter/nf_nat.h>
  26#include <net/netfilter/nf_nat_helper.h>
  27#include <net/netfilter/nf_conntrack_helper.h>
  28#include <net/netfilter/nf_conntrack_expect.h>
  29#include <net/netfilter/nf_conntrack_zones.h>
  30#include <linux/netfilter/nf_conntrack_proto_gre.h>
  31#include <linux/netfilter/nf_conntrack_pptp.h>
  32
  33#define NF_NAT_PPTP_VERSION "3.0"
  34
  35#define REQ_CID(req, off)               (*(__be16 *)((char *)(req) + (off)))
  36
  37MODULE_LICENSE("GPL");
  38MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  39MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  40MODULE_ALIAS("ip_nat_pptp");
  41
  42static void pptp_nat_expected(struct nf_conn *ct,
  43                              struct nf_conntrack_expect *exp)
  44{
  45        struct net *net = nf_ct_net(ct);
  46        const struct nf_conn *master = ct->master;
  47        struct nf_conntrack_expect *other_exp;
  48        struct nf_conntrack_tuple t;
  49        const struct nf_ct_pptp_master *ct_pptp_info;
  50        const struct nf_nat_pptp *nat_pptp_info;
  51        struct nf_nat_range range;
  52
  53        ct_pptp_info = nfct_help_data(master);
  54        nat_pptp_info = &nfct_nat(master)->help.nat_pptp_info;
  55
  56        /* And here goes the grand finale of corrosion... */
  57        if (exp->dir == IP_CT_DIR_ORIGINAL) {
  58                pr_debug("we are PNS->PAC\n");
  59                /* therefore, build tuple for PAC->PNS */
  60                t.src.l3num = AF_INET;
  61                t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  62                t.src.u.gre.key = ct_pptp_info->pac_call_id;
  63                t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  64                t.dst.u.gre.key = ct_pptp_info->pns_call_id;
  65                t.dst.protonum = IPPROTO_GRE;
  66        } else {
  67                pr_debug("we are PAC->PNS\n");
  68                /* build tuple for PNS->PAC */
  69                t.src.l3num = AF_INET;
  70                t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  71                t.src.u.gre.key = nat_pptp_info->pns_call_id;
  72                t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  73                t.dst.u.gre.key = nat_pptp_info->pac_call_id;
  74                t.dst.protonum = IPPROTO_GRE;
  75        }
  76
  77        pr_debug("trying to unexpect other dir: ");
  78        nf_ct_dump_tuple_ip(&t);
  79        other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
  80        if (other_exp) {
  81                nf_ct_unexpect_related(other_exp);
  82                nf_ct_expect_put(other_exp);
  83                pr_debug("success\n");
  84        } else {
  85                pr_debug("not found!\n");
  86        }
  87
  88        /* This must be a fresh one. */
  89        BUG_ON(ct->status & IPS_NAT_DONE_MASK);
  90
  91        /* Change src to where master sends to */
  92        range.flags = NF_NAT_RANGE_MAP_IPS;
  93        range.min_addr = range.max_addr
  94                = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
  95        if (exp->dir == IP_CT_DIR_ORIGINAL) {
  96                range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
  97                range.min_proto = range.max_proto = exp->saved_proto;
  98        }
  99        nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 100
 101        /* For DST manip, map port here to where it's expected. */
 102        range.flags = NF_NAT_RANGE_MAP_IPS;
 103        range.min_addr = range.max_addr
 104                = ct->master->tuplehash[!exp->dir].tuple.src.u3;
 105        if (exp->dir == IP_CT_DIR_REPLY) {
 106                range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 107                range.min_proto = range.max_proto = exp->saved_proto;
 108        }
 109        nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
 110}
 111
 112/* outbound packets == from PNS to PAC */
 113static int
 114pptp_outbound_pkt(struct sk_buff *skb,
 115                  struct nf_conn *ct,
 116                  enum ip_conntrack_info ctinfo,
 117                  unsigned int protoff,
 118                  struct PptpControlHeader *ctlh,
 119                  union pptp_ctrl_union *pptpReq)
 120
 121{
 122        struct nf_ct_pptp_master *ct_pptp_info;
 123        struct nf_nat_pptp *nat_pptp_info;
 124        u_int16_t msg;
 125        __be16 new_callid;
 126        unsigned int cid_off;
 127
 128        ct_pptp_info = nfct_help_data(ct);
 129        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 130
 131        new_callid = ct_pptp_info->pns_call_id;
 132
 133        switch (msg = ntohs(ctlh->messageType)) {
 134        case PPTP_OUT_CALL_REQUEST:
 135                cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 136                /* FIXME: ideally we would want to reserve a call ID
 137                 * here.  current netfilter NAT core is not able to do
 138                 * this :( For now we use TCP source port. This breaks
 139                 * multiple calls within one control session */
 140
 141                /* save original call ID in nat_info */
 142                nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 143
 144                /* don't use tcph->source since we are at a DSTmanip
 145                 * hook (e.g. PREROUTING) and pkt is not mangled yet */
 146                new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 147
 148                /* save new call ID in ct info */
 149                ct_pptp_info->pns_call_id = new_callid;
 150                break;
 151        case PPTP_IN_CALL_REPLY:
 152                cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 153                break;
 154        case PPTP_CALL_CLEAR_REQUEST:
 155                cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 156                break;
 157        default:
 158                pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
 159                         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 160                                               pptp_msg_name[0]);
 161                /* fall through */
 162        case PPTP_SET_LINK_INFO:
 163                /* only need to NAT in case PAC is behind NAT box */
 164        case PPTP_START_SESSION_REQUEST:
 165        case PPTP_START_SESSION_REPLY:
 166        case PPTP_STOP_SESSION_REQUEST:
 167        case PPTP_STOP_SESSION_REPLY:
 168        case PPTP_ECHO_REQUEST:
 169        case PPTP_ECHO_REPLY:
 170                /* no need to alter packet */
 171                return NF_ACCEPT;
 172        }
 173
 174        /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 175         * down to here */
 176        pr_debug("altering call id from 0x%04x to 0x%04x\n",
 177                 ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 178
 179        /* mangle packet */
 180        if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 181                                     cid_off + sizeof(struct pptp_pkt_hdr) +
 182                                     sizeof(struct PptpControlHeader),
 183                                     sizeof(new_callid), (char *)&new_callid,
 184                                     sizeof(new_callid)) == 0)
 185                return NF_DROP;
 186        return NF_ACCEPT;
 187}
 188
 189static void
 190pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 191             struct nf_conntrack_expect *expect_reply)
 192{
 193        const struct nf_conn *ct = expect_orig->master;
 194        struct nf_ct_pptp_master *ct_pptp_info;
 195        struct nf_nat_pptp *nat_pptp_info;
 196
 197        ct_pptp_info = nfct_help_data(ct);
 198        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 199
 200        /* save original PAC call ID in nat_info */
 201        nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 202
 203        /* alter expectation for PNS->PAC direction */
 204        expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 205        expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 206        expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 207        expect_orig->dir = IP_CT_DIR_ORIGINAL;
 208
 209        /* alter expectation for PAC->PNS direction */
 210        expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 211        expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 212        expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 213        expect_reply->dir = IP_CT_DIR_REPLY;
 214}
 215
 216/* inbound packets == from PAC to PNS */
 217static int
 218pptp_inbound_pkt(struct sk_buff *skb,
 219                 struct nf_conn *ct,
 220                 enum ip_conntrack_info ctinfo,
 221                 unsigned int protoff,
 222                 struct PptpControlHeader *ctlh,
 223                 union pptp_ctrl_union *pptpReq)
 224{
 225        const struct nf_nat_pptp *nat_pptp_info;
 226        u_int16_t msg;
 227        __be16 new_pcid;
 228        unsigned int pcid_off;
 229
 230        nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 231        new_pcid = nat_pptp_info->pns_call_id;
 232
 233        switch (msg = ntohs(ctlh->messageType)) {
 234        case PPTP_OUT_CALL_REPLY:
 235                pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 236                break;
 237        case PPTP_IN_CALL_CONNECT:
 238                pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 239                break;
 240        case PPTP_IN_CALL_REQUEST:
 241                /* only need to nat in case PAC is behind NAT box */
 242                return NF_ACCEPT;
 243        case PPTP_WAN_ERROR_NOTIFY:
 244                pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 245                break;
 246        case PPTP_CALL_DISCONNECT_NOTIFY:
 247                pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 248                break;
 249        case PPTP_SET_LINK_INFO:
 250                pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 251                break;
 252        default:
 253                pr_debug("unknown inbound packet %s\n",
 254                         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 255                                               pptp_msg_name[0]);
 256                /* fall through */
 257        case PPTP_START_SESSION_REQUEST:
 258        case PPTP_START_SESSION_REPLY:
 259        case PPTP_STOP_SESSION_REQUEST:
 260        case PPTP_STOP_SESSION_REPLY:
 261        case PPTP_ECHO_REQUEST:
 262        case PPTP_ECHO_REPLY:
 263                /* no need to alter packet */
 264                return NF_ACCEPT;
 265        }
 266
 267        /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 268         * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 269
 270        /* mangle packet */
 271        pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
 272                 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 273
 274        if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 275                                     pcid_off + sizeof(struct pptp_pkt_hdr) +
 276                                     sizeof(struct PptpControlHeader),
 277                                     sizeof(new_pcid), (char *)&new_pcid,
 278                                     sizeof(new_pcid)) == 0)
 279                return NF_DROP;
 280        return NF_ACCEPT;
 281}
 282
 283static int __init nf_nat_helper_pptp_init(void)
 284{
 285        nf_nat_need_gre();
 286
 287        BUG_ON(nf_nat_pptp_hook_outbound != NULL);
 288        RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 289
 290        BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 291        RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 292
 293        BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 294        RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 295
 296        BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 297        RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 298        return 0;
 299}
 300
 301static void __exit nf_nat_helper_pptp_fini(void)
 302{
 303        RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, NULL);
 304        RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, NULL);
 305        RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, NULL);
 306        RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, NULL);
 307        synchronize_rcu();
 308}
 309
 310module_init(nf_nat_helper_pptp_init);
 311module_exit(nf_nat_helper_pptp_fini);
 312