blob: 15fe8f649510398f6df0e7c2e665fd28b0b0fd47 [file] [log] [blame]
Patrick McHardycdd289a2007-02-07 15:09:46 -08001/*
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
25MODULE_LICENSE("GPL");
26MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
27MODULE_DESCRIPTION("x_tables TCP MSS modification module");
28MODULE_ALIAS("ipt_TCPMSS");
29MODULE_ALIAS("ip6t_TCPMSS");
30
31static inline unsigned int
32optlen(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
41static int
42tcpmss_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 Melod56f90a2007-04-10 20:50:43 -070057 tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff);
Patrick McHardycdd289a2007-02-07 15:09:46 -080058
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 Melod56f90a2007-04-10 20:50:43 -0700116 tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff);
Patrick McHardycdd289a2007-02-07 15:09:46 -0800117 }
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
140static unsigned int
141xt_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 Meloeddc9ec2007-04-20 22:47:35 -0700148 struct iphdr *iph = ip_hdr(*pskb);
Patrick McHardycdd289a2007-02-07 15:09:46 -0800149 __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 Meloeddc9ec2007-04-20 22:47:35 -0700157 iph = ip_hdr(*pskb);
Patrick McHardycdd289a2007-02-07 15:09:46 -0800158 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)
166static unsigned int
167xt_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 Melo0660e032007-04-25 17:54:47 -0700174 struct ipv6hdr *ipv6h = ipv6_hdr(*pskb);
Patrick McHardycdd289a2007-02-07 15:09:46 -0800175 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 Melo0660e032007-04-25 17:54:47 -0700190 ipv6h = ipv6_hdr(*pskb);
Patrick McHardycdd289a2007-02-07 15:09:46 -0800191 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 */
200static 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
212static int
213xt_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)
237static int
238xt_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
262static 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
285static int __init xt_tcpmss_init(void)
286{
287 return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
288}
289
290static void __exit xt_tcpmss_fini(void)
291{
292 xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
293}
294
295module_init(xt_tcpmss_init);
296module_exit(xt_tcpmss_fini);