net/ipv4/netfilter/nf_nat_pptp.c

   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
  37 MODULE_LICENSE("GPL");
  38 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  39 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  40 MODULE_ALIAS("ip_nat_pptp");
  41
  42 static 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 */
 113 static int
 114 pptp_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                          pptp_msg_name(msg));
 160                 /* fall through */
 161         case PPTP_SET_LINK_INFO:
 162                 /* only need to NAT in case PAC is behind NAT box */
 163         case PPTP_START_SESSION_REQUEST:
 164         case PPTP_START_SESSION_REPLY:
 165         case PPTP_STOP_SESSION_REQUEST:
 166         case PPTP_STOP_SESSION_REPLY:
 167         case PPTP_ECHO_REQUEST:
 168         case PPTP_ECHO_REPLY:
 169                 /* no need to alter packet */
 170                 return NF_ACCEPT;
 171         }
 172
 173         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 174          * down to here */
 175         pr_debug("altering call id from 0x%04x to 0x%04x\n",
 176                  ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 177
 178         /* mangle packet */
 179         if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 180                                      cid_off + sizeof(struct pptp_pkt_hdr) +
 181                                      sizeof(struct PptpControlHeader),
 182                                      sizeof(new_callid), (char *)&new_callid,
 183                                      sizeof(new_callid)) == 0)
 184                 return NF_DROP;
 185         return NF_ACCEPT;
 186 }
 187
 188 static void
 189 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 190              struct nf_conntrack_expect *expect_reply)
 191 {
 192         const struct nf_conn *ct = expect_orig->master;
 193         struct nf_ct_pptp_master *ct_pptp_info;
 194         struct nf_nat_pptp *nat_pptp_info;
 195
 196         ct_pptp_info = nfct_help_data(ct);
 197         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 198
 199         /* save original PAC call ID in nat_info */
 200         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 201
 202         /* alter expectation for PNS->PAC direction */
 203         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 204         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 205         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 206         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 207
 208         /* alter expectation for PAC->PNS direction */
 209         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 210         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 211         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 212         expect_reply->dir = IP_CT_DIR_REPLY;
 213 }
 214
 215 /* inbound packets == from PAC to PNS */
 216 static int
 217 pptp_inbound_pkt(struct sk_buff *skb,
 218                  struct nf_conn *ct,
 219                  enum ip_conntrack_info ctinfo,
 220                  unsigned int protoff,
 221                  struct PptpControlHeader *ctlh,
 222                  union pptp_ctrl_union *pptpReq)
 223 {
 224         const struct nf_nat_pptp *nat_pptp_info;
 225         u_int16_t msg;
 226         __be16 new_pcid;
 227         unsigned int pcid_off;
 228
 229         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 230         new_pcid = nat_pptp_info->pns_call_id;
 231
 232         switch (msg = ntohs(ctlh->messageType)) {
 233         case PPTP_OUT_CALL_REPLY:
 234                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 235                 break;
 236         case PPTP_IN_CALL_CONNECT:
 237                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 238                 break;
 239         case PPTP_IN_CALL_REQUEST:
 240                 /* only need to nat in case PAC is behind NAT box */
 241                 return NF_ACCEPT;
 242         case PPTP_WAN_ERROR_NOTIFY:
 243                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 244                 break;
 245         case PPTP_CALL_DISCONNECT_NOTIFY:
 246                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 247                 break;
 248         case PPTP_SET_LINK_INFO:
 249                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 250                 break;
 251         default:
 252                 pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
 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, protoff,
 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
 280 static 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_INIT_POINTER(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 286
 287         BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 288         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 289
 290         BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 291         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 292
 293         BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 294         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 295         return 0;
 296 }
 297
 298 static void __exit nf_nat_helper_pptp_fini(void)
 299 {
 300         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, NULL);
 301         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, NULL);
 302         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, NULL);
 303         RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, NULL);
 304         synchronize_rcu();
 305 }
 306
 307 module_init(nf_nat_helper_pptp_init);
 308 module_exit(nf_nat_helper_pptp_fini);