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