Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 1 | /* |
| 2 | * This is a module which is used for setting the MSS option in TCP packets. |
| 3 | * |
| 4 | * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca> |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License version 2 as |
| 8 | * published by the Free Software Foundation. |
| 9 | */ |
| 10 | |
| 11 | #include <linux/module.h> |
| 12 | #include <linux/skbuff.h> |
| 13 | #include <linux/ip.h> |
| 14 | #include <linux/ipv6.h> |
| 15 | #include <linux/tcp.h> |
| 16 | #include <net/ipv6.h> |
| 17 | #include <net/tcp.h> |
| 18 | |
| 19 | #include <linux/netfilter_ipv4/ip_tables.h> |
| 20 | #include <linux/netfilter_ipv6/ip6_tables.h> |
| 21 | #include <linux/netfilter/x_tables.h> |
| 22 | #include <linux/netfilter/xt_tcpudp.h> |
| 23 | #include <linux/netfilter/xt_TCPMSS.h> |
| 24 | |
| 25 | MODULE_LICENSE("GPL"); |
| 26 | MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>"); |
| 27 | MODULE_DESCRIPTION("x_tables TCP MSS modification module"); |
| 28 | MODULE_ALIAS("ipt_TCPMSS"); |
| 29 | MODULE_ALIAS("ip6t_TCPMSS"); |
| 30 | |
| 31 | static inline unsigned int |
| 32 | optlen(const u_int8_t *opt, unsigned int offset) |
| 33 | { |
| 34 | /* Beware zero-length options: make finite progress */ |
| 35 | if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0) |
| 36 | return 1; |
| 37 | else |
| 38 | return opt[offset+1]; |
| 39 | } |
| 40 | |
| 41 | static int |
| 42 | tcpmss_mangle_packet(struct sk_buff **pskb, |
| 43 | const struct xt_tcpmss_info *info, |
| 44 | unsigned int tcphoff, |
| 45 | unsigned int minlen) |
| 46 | { |
| 47 | struct tcphdr *tcph; |
| 48 | unsigned int tcplen, i; |
| 49 | __be16 oldval; |
| 50 | u16 newmss; |
| 51 | u8 *opt; |
| 52 | |
| 53 | if (!skb_make_writable(pskb, (*pskb)->len)) |
| 54 | return -1; |
| 55 | |
| 56 | tcplen = (*pskb)->len - tcphoff; |
Arnaldo Carvalho de Melo | d56f90a | 2007-04-10 20:50:43 -0700 | [diff] [blame] | 57 | tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 58 | |
| 59 | /* Since it passed flags test in tcp match, we know it is is |
| 60 | not a fragment, and has data >= tcp header length. SYN |
| 61 | packets should not contain data: if they did, then we risk |
| 62 | running over MTU, sending Frag Needed and breaking things |
| 63 | badly. --RR */ |
| 64 | if (tcplen != tcph->doff*4) { |
| 65 | if (net_ratelimit()) |
| 66 | printk(KERN_ERR "xt_TCPMSS: bad length (%u bytes)\n", |
| 67 | (*pskb)->len); |
| 68 | return -1; |
| 69 | } |
| 70 | |
| 71 | if (info->mss == XT_TCPMSS_CLAMP_PMTU) { |
| 72 | if (dst_mtu((*pskb)->dst) <= minlen) { |
| 73 | if (net_ratelimit()) |
| 74 | printk(KERN_ERR "xt_TCPMSS: " |
| 75 | "unknown or invalid path-MTU (%u)\n", |
| 76 | dst_mtu((*pskb)->dst)); |
| 77 | return -1; |
| 78 | } |
| 79 | newmss = dst_mtu((*pskb)->dst) - minlen; |
| 80 | } else |
| 81 | newmss = info->mss; |
| 82 | |
| 83 | opt = (u_int8_t *)tcph; |
| 84 | for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) { |
| 85 | if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS && |
| 86 | opt[i+1] == TCPOLEN_MSS) { |
| 87 | u_int16_t oldmss; |
| 88 | |
| 89 | oldmss = (opt[i+2] << 8) | opt[i+3]; |
| 90 | |
| 91 | if (info->mss == XT_TCPMSS_CLAMP_PMTU && |
| 92 | oldmss <= newmss) |
| 93 | return 0; |
| 94 | |
| 95 | opt[i+2] = (newmss & 0xff00) >> 8; |
| 96 | opt[i+3] = (newmss & 0x00ff); |
| 97 | |
| 98 | nf_proto_csum_replace2(&tcph->check, *pskb, |
| 99 | htons(oldmss), htons(newmss), 0); |
| 100 | return 0; |
| 101 | } |
| 102 | } |
| 103 | |
| 104 | /* |
| 105 | * MSS Option not found ?! add it.. |
| 106 | */ |
| 107 | if (skb_tailroom((*pskb)) < TCPOLEN_MSS) { |
| 108 | struct sk_buff *newskb; |
| 109 | |
| 110 | newskb = skb_copy_expand(*pskb, skb_headroom(*pskb), |
| 111 | TCPOLEN_MSS, GFP_ATOMIC); |
| 112 | if (!newskb) |
| 113 | return -1; |
| 114 | kfree_skb(*pskb); |
| 115 | *pskb = newskb; |
Arnaldo Carvalho de Melo | d56f90a | 2007-04-10 20:50:43 -0700 | [diff] [blame] | 116 | tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 117 | } |
| 118 | |
| 119 | skb_put((*pskb), TCPOLEN_MSS); |
| 120 | |
| 121 | opt = (u_int8_t *)tcph + sizeof(struct tcphdr); |
| 122 | memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr)); |
| 123 | |
| 124 | nf_proto_csum_replace2(&tcph->check, *pskb, |
| 125 | htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1); |
| 126 | opt[0] = TCPOPT_MSS; |
| 127 | opt[1] = TCPOLEN_MSS; |
| 128 | opt[2] = (newmss & 0xff00) >> 8; |
| 129 | opt[3] = (newmss & 0x00ff); |
| 130 | |
| 131 | nf_proto_csum_replace4(&tcph->check, *pskb, 0, *((__be32 *)opt), 0); |
| 132 | |
| 133 | oldval = ((__be16 *)tcph)[6]; |
| 134 | tcph->doff += TCPOLEN_MSS/4; |
| 135 | nf_proto_csum_replace2(&tcph->check, *pskb, |
| 136 | oldval, ((__be16 *)tcph)[6], 0); |
| 137 | return TCPOLEN_MSS; |
| 138 | } |
| 139 | |
| 140 | static unsigned int |
| 141 | xt_tcpmss_target4(struct sk_buff **pskb, |
| 142 | const struct net_device *in, |
| 143 | const struct net_device *out, |
| 144 | unsigned int hooknum, |
| 145 | const struct xt_target *target, |
| 146 | const void *targinfo) |
| 147 | { |
Arnaldo Carvalho de Melo | eddc9ec | 2007-04-20 22:47:35 -0700 | [diff] [blame] | 148 | struct iphdr *iph = ip_hdr(*pskb); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 149 | __be16 newlen; |
| 150 | int ret; |
| 151 | |
| 152 | ret = tcpmss_mangle_packet(pskb, targinfo, iph->ihl * 4, |
| 153 | sizeof(*iph) + sizeof(struct tcphdr)); |
| 154 | if (ret < 0) |
| 155 | return NF_DROP; |
| 156 | if (ret > 0) { |
Arnaldo Carvalho de Melo | eddc9ec | 2007-04-20 22:47:35 -0700 | [diff] [blame] | 157 | iph = ip_hdr(*pskb); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 158 | newlen = htons(ntohs(iph->tot_len) + ret); |
| 159 | nf_csum_replace2(&iph->check, iph->tot_len, newlen); |
| 160 | iph->tot_len = newlen; |
| 161 | } |
| 162 | return XT_CONTINUE; |
| 163 | } |
| 164 | |
| 165 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) |
| 166 | static unsigned int |
| 167 | xt_tcpmss_target6(struct sk_buff **pskb, |
| 168 | const struct net_device *in, |
| 169 | const struct net_device *out, |
| 170 | unsigned int hooknum, |
| 171 | const struct xt_target *target, |
| 172 | const void *targinfo) |
| 173 | { |
Arnaldo Carvalho de Melo | 0660e03 | 2007-04-25 17:54:47 -0700 | [diff] [blame] | 174 | struct ipv6hdr *ipv6h = ipv6_hdr(*pskb); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 175 | u8 nexthdr; |
| 176 | int tcphoff; |
| 177 | int ret; |
| 178 | |
| 179 | nexthdr = ipv6h->nexthdr; |
| 180 | tcphoff = ipv6_skip_exthdr(*pskb, sizeof(*ipv6h), &nexthdr); |
| 181 | if (tcphoff < 0) { |
| 182 | WARN_ON(1); |
| 183 | return NF_DROP; |
| 184 | } |
| 185 | ret = tcpmss_mangle_packet(pskb, targinfo, tcphoff, |
| 186 | sizeof(*ipv6h) + sizeof(struct tcphdr)); |
| 187 | if (ret < 0) |
| 188 | return NF_DROP; |
| 189 | if (ret > 0) { |
Arnaldo Carvalho de Melo | 0660e03 | 2007-04-25 17:54:47 -0700 | [diff] [blame] | 190 | ipv6h = ipv6_hdr(*pskb); |
Patrick McHardy | cdd289a | 2007-02-07 15:09:46 -0800 | [diff] [blame] | 191 | ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret); |
| 192 | } |
| 193 | return XT_CONTINUE; |
| 194 | } |
| 195 | #endif |
| 196 | |
| 197 | #define TH_SYN 0x02 |
| 198 | |
| 199 | /* Must specify -p tcp --syn */ |
| 200 | static inline int find_syn_match(const struct xt_entry_match *m) |
| 201 | { |
| 202 | const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data; |
| 203 | |
| 204 | if (strcmp(m->u.kernel.match->name, "tcp") == 0 && |
| 205 | tcpinfo->flg_cmp & TH_SYN && |
| 206 | !(tcpinfo->invflags & XT_TCP_INV_FLAGS)) |
| 207 | return 1; |
| 208 | |
| 209 | return 0; |
| 210 | } |
| 211 | |
| 212 | static int |
| 213 | xt_tcpmss_checkentry4(const char *tablename, |
| 214 | const void *entry, |
| 215 | const struct xt_target *target, |
| 216 | void *targinfo, |
| 217 | unsigned int hook_mask) |
| 218 | { |
| 219 | const struct xt_tcpmss_info *info = targinfo; |
| 220 | const struct ipt_entry *e = entry; |
| 221 | |
| 222 | if (info->mss == XT_TCPMSS_CLAMP_PMTU && |
| 223 | (hook_mask & ~((1 << NF_IP_FORWARD) | |
| 224 | (1 << NF_IP_LOCAL_OUT) | |
| 225 | (1 << NF_IP_POST_ROUTING))) != 0) { |
| 226 | printk("xt_TCPMSS: path-MTU clamping only supported in " |
| 227 | "FORWARD, OUTPUT and POSTROUTING hooks\n"); |
| 228 | return 0; |
| 229 | } |
| 230 | if (IPT_MATCH_ITERATE(e, find_syn_match)) |
| 231 | return 1; |
| 232 | printk("xt_TCPMSS: Only works on TCP SYN packets\n"); |
| 233 | return 0; |
| 234 | } |
| 235 | |
| 236 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) |
| 237 | static int |
| 238 | xt_tcpmss_checkentry6(const char *tablename, |
| 239 | const void *entry, |
| 240 | const struct xt_target *target, |
| 241 | void *targinfo, |
| 242 | unsigned int hook_mask) |
| 243 | { |
| 244 | const struct xt_tcpmss_info *info = targinfo; |
| 245 | const struct ip6t_entry *e = entry; |
| 246 | |
| 247 | if (info->mss == XT_TCPMSS_CLAMP_PMTU && |
| 248 | (hook_mask & ~((1 << NF_IP6_FORWARD) | |
| 249 | (1 << NF_IP6_LOCAL_OUT) | |
| 250 | (1 << NF_IP6_POST_ROUTING))) != 0) { |
| 251 | printk("xt_TCPMSS: path-MTU clamping only supported in " |
| 252 | "FORWARD, OUTPUT and POSTROUTING hooks\n"); |
| 253 | return 0; |
| 254 | } |
| 255 | if (IP6T_MATCH_ITERATE(e, find_syn_match)) |
| 256 | return 1; |
| 257 | printk("xt_TCPMSS: Only works on TCP SYN packets\n"); |
| 258 | return 0; |
| 259 | } |
| 260 | #endif |
| 261 | |
| 262 | static struct xt_target xt_tcpmss_reg[] = { |
| 263 | { |
| 264 | .family = AF_INET, |
| 265 | .name = "TCPMSS", |
| 266 | .checkentry = xt_tcpmss_checkentry4, |
| 267 | .target = xt_tcpmss_target4, |
| 268 | .targetsize = sizeof(struct xt_tcpmss_info), |
| 269 | .proto = IPPROTO_TCP, |
| 270 | .me = THIS_MODULE, |
| 271 | }, |
| 272 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) |
| 273 | { |
| 274 | .family = AF_INET6, |
| 275 | .name = "TCPMSS", |
| 276 | .checkentry = xt_tcpmss_checkentry6, |
| 277 | .target = xt_tcpmss_target6, |
| 278 | .targetsize = sizeof(struct xt_tcpmss_info), |
| 279 | .proto = IPPROTO_TCP, |
| 280 | .me = THIS_MODULE, |
| 281 | }, |
| 282 | #endif |
| 283 | }; |
| 284 | |
| 285 | static int __init xt_tcpmss_init(void) |
| 286 | { |
| 287 | return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg)); |
| 288 | } |
| 289 | |
| 290 | static void __exit xt_tcpmss_fini(void) |
| 291 | { |
| 292 | xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg)); |
| 293 | } |
| 294 | |
| 295 | module_init(xt_tcpmss_init); |
| 296 | module_exit(xt_tcpmss_fini); |