]>
Commit | Line | Data |
---|---|---|
cdd289a2 PM |
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 | ||
37d41879 | 53 | if (!skb_make_writable(*pskb, (*pskb)->len)) |
cdd289a2 PM |
54 | return -1; |
55 | ||
56 | tcplen = (*pskb)->len - tcphoff; | |
d56f90a7 | 57 | tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff); |
cdd289a2 PM |
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; | |
7c4e36bc | 96 | opt[i+3] = newmss & 0x00ff; |
cdd289a2 PM |
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) { | |
2ca7b0ac HX |
108 | if (pskb_expand_head(*pskb, 0, |
109 | TCPOLEN_MSS - skb_tailroom(*pskb), | |
110 | GFP_ATOMIC)) | |
cdd289a2 | 111 | return -1; |
d56f90a7 | 112 | tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff); |
cdd289a2 PM |
113 | } |
114 | ||
115 | skb_put((*pskb), TCPOLEN_MSS); | |
116 | ||
117 | opt = (u_int8_t *)tcph + sizeof(struct tcphdr); | |
118 | memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr)); | |
119 | ||
120 | nf_proto_csum_replace2(&tcph->check, *pskb, | |
121 | htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1); | |
122 | opt[0] = TCPOPT_MSS; | |
123 | opt[1] = TCPOLEN_MSS; | |
124 | opt[2] = (newmss & 0xff00) >> 8; | |
7c4e36bc | 125 | opt[3] = newmss & 0x00ff; |
cdd289a2 PM |
126 | |
127 | nf_proto_csum_replace4(&tcph->check, *pskb, 0, *((__be32 *)opt), 0); | |
128 | ||
129 | oldval = ((__be16 *)tcph)[6]; | |
130 | tcph->doff += TCPOLEN_MSS/4; | |
131 | nf_proto_csum_replace2(&tcph->check, *pskb, | |
132 | oldval, ((__be16 *)tcph)[6], 0); | |
133 | return TCPOLEN_MSS; | |
134 | } | |
135 | ||
136 | static unsigned int | |
137 | xt_tcpmss_target4(struct sk_buff **pskb, | |
138 | const struct net_device *in, | |
139 | const struct net_device *out, | |
140 | unsigned int hooknum, | |
141 | const struct xt_target *target, | |
142 | const void *targinfo) | |
143 | { | |
eddc9ec5 | 144 | struct iphdr *iph = ip_hdr(*pskb); |
cdd289a2 PM |
145 | __be16 newlen; |
146 | int ret; | |
147 | ||
148 | ret = tcpmss_mangle_packet(pskb, targinfo, iph->ihl * 4, | |
149 | sizeof(*iph) + sizeof(struct tcphdr)); | |
150 | if (ret < 0) | |
151 | return NF_DROP; | |
152 | if (ret > 0) { | |
eddc9ec5 | 153 | iph = ip_hdr(*pskb); |
cdd289a2 PM |
154 | newlen = htons(ntohs(iph->tot_len) + ret); |
155 | nf_csum_replace2(&iph->check, iph->tot_len, newlen); | |
156 | iph->tot_len = newlen; | |
157 | } | |
158 | return XT_CONTINUE; | |
159 | } | |
160 | ||
161 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) | |
162 | static unsigned int | |
163 | xt_tcpmss_target6(struct sk_buff **pskb, | |
164 | const struct net_device *in, | |
165 | const struct net_device *out, | |
166 | unsigned int hooknum, | |
167 | const struct xt_target *target, | |
168 | const void *targinfo) | |
169 | { | |
0660e03f | 170 | struct ipv6hdr *ipv6h = ipv6_hdr(*pskb); |
cdd289a2 PM |
171 | u8 nexthdr; |
172 | int tcphoff; | |
173 | int ret; | |
174 | ||
175 | nexthdr = ipv6h->nexthdr; | |
176 | tcphoff = ipv6_skip_exthdr(*pskb, sizeof(*ipv6h), &nexthdr); | |
177 | if (tcphoff < 0) { | |
178 | WARN_ON(1); | |
179 | return NF_DROP; | |
180 | } | |
181 | ret = tcpmss_mangle_packet(pskb, targinfo, tcphoff, | |
182 | sizeof(*ipv6h) + sizeof(struct tcphdr)); | |
183 | if (ret < 0) | |
184 | return NF_DROP; | |
185 | if (ret > 0) { | |
0660e03f | 186 | ipv6h = ipv6_hdr(*pskb); |
cdd289a2 PM |
187 | ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret); |
188 | } | |
189 | return XT_CONTINUE; | |
190 | } | |
191 | #endif | |
192 | ||
193 | #define TH_SYN 0x02 | |
194 | ||
195 | /* Must specify -p tcp --syn */ | |
e1931b78 | 196 | static inline bool find_syn_match(const struct xt_entry_match *m) |
cdd289a2 PM |
197 | { |
198 | const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data; | |
199 | ||
200 | if (strcmp(m->u.kernel.match->name, "tcp") == 0 && | |
201 | tcpinfo->flg_cmp & TH_SYN && | |
202 | !(tcpinfo->invflags & XT_TCP_INV_FLAGS)) | |
e1931b78 | 203 | return true; |
cdd289a2 | 204 | |
e1931b78 | 205 | return false; |
cdd289a2 PM |
206 | } |
207 | ||
e1931b78 | 208 | static bool |
cdd289a2 PM |
209 | xt_tcpmss_checkentry4(const char *tablename, |
210 | const void *entry, | |
211 | const struct xt_target *target, | |
212 | void *targinfo, | |
213 | unsigned int hook_mask) | |
214 | { | |
215 | const struct xt_tcpmss_info *info = targinfo; | |
216 | const struct ipt_entry *e = entry; | |
217 | ||
218 | if (info->mss == XT_TCPMSS_CLAMP_PMTU && | |
219 | (hook_mask & ~((1 << NF_IP_FORWARD) | | |
220 | (1 << NF_IP_LOCAL_OUT) | | |
221 | (1 << NF_IP_POST_ROUTING))) != 0) { | |
222 | printk("xt_TCPMSS: path-MTU clamping only supported in " | |
223 | "FORWARD, OUTPUT and POSTROUTING hooks\n"); | |
e1931b78 | 224 | return false; |
cdd289a2 PM |
225 | } |
226 | if (IPT_MATCH_ITERATE(e, find_syn_match)) | |
e1931b78 | 227 | return true; |
cdd289a2 | 228 | printk("xt_TCPMSS: Only works on TCP SYN packets\n"); |
e1931b78 | 229 | return false; |
cdd289a2 PM |
230 | } |
231 | ||
232 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) | |
e1931b78 | 233 | static bool |
cdd289a2 PM |
234 | xt_tcpmss_checkentry6(const char *tablename, |
235 | const void *entry, | |
236 | const struct xt_target *target, | |
237 | void *targinfo, | |
238 | unsigned int hook_mask) | |
239 | { | |
240 | const struct xt_tcpmss_info *info = targinfo; | |
241 | const struct ip6t_entry *e = entry; | |
242 | ||
243 | if (info->mss == XT_TCPMSS_CLAMP_PMTU && | |
244 | (hook_mask & ~((1 << NF_IP6_FORWARD) | | |
245 | (1 << NF_IP6_LOCAL_OUT) | | |
246 | (1 << NF_IP6_POST_ROUTING))) != 0) { | |
247 | printk("xt_TCPMSS: path-MTU clamping only supported in " | |
248 | "FORWARD, OUTPUT and POSTROUTING hooks\n"); | |
e1931b78 | 249 | return false; |
cdd289a2 PM |
250 | } |
251 | if (IP6T_MATCH_ITERATE(e, find_syn_match)) | |
e1931b78 | 252 | return true; |
cdd289a2 | 253 | printk("xt_TCPMSS: Only works on TCP SYN packets\n"); |
e1931b78 | 254 | return false; |
cdd289a2 PM |
255 | } |
256 | #endif | |
257 | ||
9f15c530 | 258 | static struct xt_target xt_tcpmss_reg[] __read_mostly = { |
cdd289a2 PM |
259 | { |
260 | .family = AF_INET, | |
261 | .name = "TCPMSS", | |
262 | .checkentry = xt_tcpmss_checkentry4, | |
263 | .target = xt_tcpmss_target4, | |
264 | .targetsize = sizeof(struct xt_tcpmss_info), | |
265 | .proto = IPPROTO_TCP, | |
266 | .me = THIS_MODULE, | |
267 | }, | |
268 | #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE) | |
269 | { | |
270 | .family = AF_INET6, | |
271 | .name = "TCPMSS", | |
272 | .checkentry = xt_tcpmss_checkentry6, | |
273 | .target = xt_tcpmss_target6, | |
274 | .targetsize = sizeof(struct xt_tcpmss_info), | |
275 | .proto = IPPROTO_TCP, | |
276 | .me = THIS_MODULE, | |
277 | }, | |
278 | #endif | |
279 | }; | |
280 | ||
281 | static int __init xt_tcpmss_init(void) | |
282 | { | |
283 | return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg)); | |
284 | } | |
285 | ||
286 | static void __exit xt_tcpmss_fini(void) | |
287 | { | |
288 | xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg)); | |
289 | } | |
290 | ||
291 | module_init(xt_tcpmss_init); | |
292 | module_exit(xt_tcpmss_fini); |