1 /* Kernel module to match L2TP header parameters. */ 2 3 /* (C) 2013 James Chapman <jchapman@katalix.com> 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License version 2 as 7 * published by the Free Software Foundation. 8 */ 9 10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 11 #include <linux/module.h> 12 #include <linux/skbuff.h> 13 #include <linux/if_ether.h> 14 #include <net/ip.h> 15 #include <linux/ipv6.h> 16 #include <net/ipv6.h> 17 #include <net/udp.h> 18 #include <linux/l2tp.h> 19 20 #include <linux/netfilter_ipv4.h> 21 #include <linux/netfilter_ipv6.h> 22 #include <linux/netfilter_ipv4/ip_tables.h> 23 #include <linux/netfilter_ipv6/ip6_tables.h> 24 #include <linux/netfilter/x_tables.h> 25 #include <linux/netfilter/xt_tcpudp.h> 26 #include <linux/netfilter/xt_l2tp.h> 27 28 /* L2TP header masks */ 29 #define L2TP_HDR_T_BIT 0x8000 30 #define L2TP_HDR_L_BIT 0x4000 31 #define L2TP_HDR_VER 0x000f 32 33 MODULE_LICENSE("GPL"); 34 MODULE_AUTHOR("James Chapman <jchapman@katalix.com>"); 35 MODULE_DESCRIPTION("Xtables: L2TP header match"); 36 MODULE_ALIAS("ipt_l2tp"); 37 MODULE_ALIAS("ip6t_l2tp"); 38 39 /* The L2TP fields that can be matched */ 40 struct l2tp_data { 41 u32 tid; 42 u32 sid; 43 u8 type; 44 u8 version; 45 }; 46 47 union l2tp_val { 48 __be16 val16[2]; 49 __be32 val32; 50 }; 51 52 static bool l2tp_match(const struct xt_l2tp_info *info, struct l2tp_data *data) 53 { 54 if ((info->flags & XT_L2TP_TYPE) && (info->type != data->type)) 55 return false; 56 57 if ((info->flags & XT_L2TP_VERSION) && (info->version != data->version)) 58 return false; 59 60 /* Check tid only for L2TPv3 control or any L2TPv2 packets */ 61 if ((info->flags & XT_L2TP_TID) && 62 ((data->type == XT_L2TP_TYPE_CONTROL) || (data->version == 2)) && 63 (info->tid != data->tid)) 64 return false; 65 66 /* Check sid only for L2TP data packets */ 67 if ((info->flags & XT_L2TP_SID) && (data->type == XT_L2TP_TYPE_DATA) && 68 (info->sid != data->sid)) 69 return false; 70 71 return true; 72 } 73 74 /* Parse L2TP header fields when UDP encapsulation is used. Handles 75 * L2TPv2 and L2TPv3. Note the L2TPv3 control and data packets have a 76 * different format. See 77 * RFC2661, Section 3.1, L2TPv2 Header Format 78 * RFC3931, Section 3.2.1, L2TPv3 Control Message Header 79 * RFC3931, Section 3.2.2, L2TPv3 Data Message Header 80 * RFC3931, Section 4.1.2.1, L2TPv3 Session Header over UDP 81 */ 82 static bool l2tp_udp_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff) 83 { 84 const struct xt_l2tp_info *info = par->matchinfo; 85 int uhlen = sizeof(struct udphdr); 86 int offs = thoff + uhlen; 87 union l2tp_val *lh; 88 union l2tp_val lhbuf; 89 u16 flags; 90 struct l2tp_data data = { 0, }; 91 92 if (par->fragoff != 0) 93 return false; 94 95 /* Extract L2TP header fields. The flags in the first 16 bits 96 * tell us where the other fields are. 97 */ 98 lh = skb_header_pointer(skb, offs, 2, &lhbuf); 99 if (lh == NULL) 100 return false; 101 102 flags = ntohs(lh->val16[0]); 103 if (flags & L2TP_HDR_T_BIT) 104 data.type = XT_L2TP_TYPE_CONTROL; 105 else 106 data.type = XT_L2TP_TYPE_DATA; 107 data.version = (u8) flags & L2TP_HDR_VER; 108 109 /* Now extract the L2TP tid/sid. These are in different places 110 * for L2TPv2 (rfc2661) and L2TPv3 (rfc3931). For L2TPv2, we 111 * must also check to see if the length field is present, 112 * since this affects the offsets into the packet of the 113 * tid/sid fields. 114 */ 115 if (data.version == 3) { 116 lh = skb_header_pointer(skb, offs + 4, 4, &lhbuf); 117 if (lh == NULL) 118 return false; 119 if (data.type == XT_L2TP_TYPE_CONTROL) 120 data.tid = ntohl(lh->val32); 121 else 122 data.sid = ntohl(lh->val32); 123 } else if (data.version == 2) { 124 if (flags & L2TP_HDR_L_BIT) 125 offs += 2; 126 lh = skb_header_pointer(skb, offs + 2, 4, &lhbuf); 127 if (lh == NULL) 128 return false; 129 data.tid = (u32) ntohs(lh->val16[0]); 130 data.sid = (u32) ntohs(lh->val16[1]); 131 } else 132 return false; 133 134 return l2tp_match(info, &data); 135 } 136 137 /* Parse L2TP header fields for IP encapsulation (no UDP header). 138 * L2TPv3 data packets have a different form with IP encap. See 139 * RC3931, Section 4.1.1.1, L2TPv3 Session Header over IP. 140 * RC3931, Section 4.1.1.2, L2TPv3 Control and Data Traffic over IP. 141 */ 142 static bool l2tp_ip_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff) 143 { 144 const struct xt_l2tp_info *info = par->matchinfo; 145 union l2tp_val *lh; 146 union l2tp_val lhbuf; 147 struct l2tp_data data = { 0, }; 148 149 /* For IP encap, the L2TP sid is the first 32-bits. */ 150 lh = skb_header_pointer(skb, thoff, sizeof(lhbuf), &lhbuf); 151 if (lh == NULL) 152 return false; 153 if (lh->val32 == 0) { 154 /* Must be a control packet. The L2TP tid is further 155 * into the packet. 156 */ 157 data.type = XT_L2TP_TYPE_CONTROL; 158 lh = skb_header_pointer(skb, thoff + 8, sizeof(lhbuf), 159 &lhbuf); 160 if (lh == NULL) 161 return false; 162 data.tid = ntohl(lh->val32); 163 } else { 164 data.sid = ntohl(lh->val32); 165 data.type = XT_L2TP_TYPE_DATA; 166 } 167 168 data.version = 3; 169 170 return l2tp_match(info, &data); 171 } 172 173 static bool l2tp_mt4(const struct sk_buff *skb, struct xt_action_param *par) 174 { 175 struct iphdr *iph = ip_hdr(skb); 176 u8 ipproto = iph->protocol; 177 178 /* l2tp_mt_check4 already restricts the transport protocol */ 179 switch (ipproto) { 180 case IPPROTO_UDP: 181 return l2tp_udp_mt(skb, par, par->thoff); 182 case IPPROTO_L2TP: 183 return l2tp_ip_mt(skb, par, par->thoff); 184 } 185 186 return false; 187 } 188 189 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES) 190 static bool l2tp_mt6(const struct sk_buff *skb, struct xt_action_param *par) 191 { 192 unsigned int thoff = 0; 193 unsigned short fragoff = 0; 194 int ipproto; 195 196 ipproto = ipv6_find_hdr(skb, &thoff, -1, &fragoff, NULL); 197 if (fragoff != 0) 198 return false; 199 200 /* l2tp_mt_check6 already restricts the transport protocol */ 201 switch (ipproto) { 202 case IPPROTO_UDP: 203 return l2tp_udp_mt(skb, par, thoff); 204 case IPPROTO_L2TP: 205 return l2tp_ip_mt(skb, par, thoff); 206 } 207 208 return false; 209 } 210 #endif 211 212 static int l2tp_mt_check(const struct xt_mtchk_param *par) 213 { 214 const struct xt_l2tp_info *info = par->matchinfo; 215 216 /* Check for invalid flags */ 217 if (info->flags & ~(XT_L2TP_TID | XT_L2TP_SID | XT_L2TP_VERSION | 218 XT_L2TP_TYPE)) { 219 pr_info("unknown flags: %x\n", info->flags); 220 return -EINVAL; 221 } 222 223 /* At least one of tid, sid or type=control must be specified */ 224 if ((!(info->flags & XT_L2TP_TID)) && 225 (!(info->flags & XT_L2TP_SID)) && 226 ((!(info->flags & XT_L2TP_TYPE)) || 227 (info->type != XT_L2TP_TYPE_CONTROL))) { 228 pr_info("invalid flags combination: %x\n", info->flags); 229 return -EINVAL; 230 } 231 232 /* If version 2 is specified, check that incompatible params 233 * are not supplied 234 */ 235 if (info->flags & XT_L2TP_VERSION) { 236 if ((info->version < 2) || (info->version > 3)) { 237 pr_info("wrong L2TP version: %u\n", info->version); 238 return -EINVAL; 239 } 240 241 if (info->version == 2) { 242 if ((info->flags & XT_L2TP_TID) && 243 (info->tid > 0xffff)) { 244 pr_info("v2 tid > 0xffff: %u\n", info->tid); 245 return -EINVAL; 246 } 247 if ((info->flags & XT_L2TP_SID) && 248 (info->sid > 0xffff)) { 249 pr_info("v2 sid > 0xffff: %u\n", info->sid); 250 return -EINVAL; 251 } 252 } 253 } 254 255 return 0; 256 } 257 258 static int l2tp_mt_check4(const struct xt_mtchk_param *par) 259 { 260 const struct xt_l2tp_info *info = par->matchinfo; 261 const struct ipt_entry *e = par->entryinfo; 262 const struct ipt_ip *ip = &e->ip; 263 int ret; 264 265 ret = l2tp_mt_check(par); 266 if (ret != 0) 267 return ret; 268 269 if ((ip->proto != IPPROTO_UDP) && 270 (ip->proto != IPPROTO_L2TP)) { 271 pr_info("missing protocol rule (udp|l2tpip)\n"); 272 return -EINVAL; 273 } 274 275 if ((ip->proto == IPPROTO_L2TP) && 276 (info->version == 2)) { 277 pr_info("v2 doesn't support IP mode\n"); 278 return -EINVAL; 279 } 280 281 return 0; 282 } 283 284 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES) 285 static int l2tp_mt_check6(const struct xt_mtchk_param *par) 286 { 287 const struct xt_l2tp_info *info = par->matchinfo; 288 const struct ip6t_entry *e = par->entryinfo; 289 const struct ip6t_ip6 *ip = &e->ipv6; 290 int ret; 291 292 ret = l2tp_mt_check(par); 293 if (ret != 0) 294 return ret; 295 296 if ((ip->proto != IPPROTO_UDP) && 297 (ip->proto != IPPROTO_L2TP)) { 298 pr_info("missing protocol rule (udp|l2tpip)\n"); 299 return -EINVAL; 300 } 301 302 if ((ip->proto == IPPROTO_L2TP) && 303 (info->version == 2)) { 304 pr_info("v2 doesn't support IP mode\n"); 305 return -EINVAL; 306 } 307 308 return 0; 309 } 310 #endif 311 312 static struct xt_match l2tp_mt_reg[] __read_mostly = { 313 { 314 .name = "l2tp", 315 .revision = 0, 316 .family = NFPROTO_IPV4, 317 .match = l2tp_mt4, 318 .matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)), 319 .checkentry = l2tp_mt_check4, 320 .hooks = ((1 << NF_INET_PRE_ROUTING) | 321 (1 << NF_INET_LOCAL_IN) | 322 (1 << NF_INET_LOCAL_OUT) | 323 (1 << NF_INET_FORWARD)), 324 .me = THIS_MODULE, 325 }, 326 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES) 327 { 328 .name = "l2tp", 329 .revision = 0, 330 .family = NFPROTO_IPV6, 331 .match = l2tp_mt6, 332 .matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)), 333 .checkentry = l2tp_mt_check6, 334 .hooks = ((1 << NF_INET_PRE_ROUTING) | 335 (1 << NF_INET_LOCAL_IN) | 336 (1 << NF_INET_LOCAL_OUT) | 337 (1 << NF_INET_FORWARD)), 338 .me = THIS_MODULE, 339 }, 340 #endif 341 }; 342 343 static int __init l2tp_mt_init(void) 344 { 345 return xt_register_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg)); 346 } 347 348 static void __exit l2tp_mt_exit(void) 349 { 350 xt_unregister_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg)); 351 } 352 353 module_init(l2tp_mt_init); 354 module_exit(l2tp_mt_exit); 355