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 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 } 188 189 static void 190 pptp_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 */ 217 static int 218 pptp_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 } 282 283 static 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 } 300 301 static 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 } 309 310 module_init(nf_nat_helper_pptp_init); 311 module_exit(nf_nat_helper_pptp_fini); 312