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1 /* 1
2 * This is a module which is used for setting
3 *
4 * Copyright (C) 2000 Marc Boucher <marc@mbsi.
5 *
6 * This program is free software; you can redi
7 * it under the terms of the GNU General Publi
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/dst.h>
17 #include <net/flow.h>
18 #include <net/ipv6.h>
19 #include <net/route.h>
20 #include <net/tcp.h>
21
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_TCPMSS.h>
27
28 MODULE_LICENSE("GPL");
29 MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
30 MODULE_DESCRIPTION("Xtables: TCP Maximum Segme
31 MODULE_ALIAS("ipt_TCPMSS");
32 MODULE_ALIAS("ip6t_TCPMSS");
33
34 static inline unsigned int
35 optlen(const u_int8_t *opt, unsigned int offse
36 {
37 /* Beware zero-length options: make fi
38 if (opt[offset] <= TCPOPT_NOP || opt[o
39 return 1;
40 else
41 return opt[offset+1];
42 }
43
44 static int
45 tcpmss_mangle_packet(struct sk_buff *skb,
46 const struct xt_tcpmss_in
47 unsigned int in_mtu,
48 unsigned int tcphoff,
49 unsigned int minlen)
50 {
51 struct tcphdr *tcph;
52 unsigned int tcplen, i;
53 __be16 oldval;
54 u16 newmss;
55 u8 *opt;
56
57 if (!skb_make_writable(skb, skb->len))
58 return -1;
59
60 tcplen = skb->len - tcphoff;
61 tcph = (struct tcphdr *)(skb_network_h
62
63 /* Since it passed flags test in tcp m
64 not a fragment, and has data >= tcp
65 packets should not contain data: if
66 running over MTU, sending Frag Need
67 badly. --RR */
68 if (tcplen != tcph->doff*4) {
69 if (net_ratelimit())
70 printk(KERN_ERR "xt_TC
71 skb->len);
72 return -1;
73 }
74
75 if (info->mss == XT_TCPMSS_CLAMP_PMTU)
76 if (dst_mtu(skb->dst) <= minle
77 if (net_ratelimit())
78 printk(KERN_ER
79 "unknow
80 dst_mtu
81 return -1;
82 }
83 if (in_mtu <= minlen) {
84 if (net_ratelimit())
85 printk(KERN_ER
86 "invali
87 return -1;
88 }
89 newmss = min(dst_mtu(skb->dst)
90 } else
91 newmss = info->mss;
92
93 opt = (u_int8_t *)tcph;
94 for (i = sizeof(struct tcphdr); i < tc
95 if (opt[i] == TCPOPT_MSS && tc
96 opt[i+1] == TCPOLEN_MSS) {
97 u_int16_t oldmss;
98
99 oldmss = (opt[i+2] <<
100
101 /* Never increase MSS,
102 * doing so results in
103 * on MSS being set co
104 */
105 if (oldmss <= newmss)
106 return 0;
107
108 opt[i+2] = (newmss & 0
109 opt[i+3] = newmss & 0x
110
111 inet_proto_csum_replac
112
113
114 return 0;
115 }
116 }
117
118 /*
119 * MSS Option not found ?! add it..
120 */
121 if (skb_tailroom(skb) < TCPOLEN_MSS) {
122 if (pskb_expand_head(skb, 0,
123 TCPOLEN_M
124 GFP_ATOMI
125 return -1;
126 tcph = (struct tcphdr *)(skb_n
127 }
128
129 skb_put(skb, TCPOLEN_MSS);
130
131 opt = (u_int8_t *)tcph + sizeof(struct
132 memmove(opt + TCPOLEN_MSS, opt, tcplen
133
134 inet_proto_csum_replace2(&tcph->check,
135 htons(tcplen)
136 opt[0] = TCPOPT_MSS;
137 opt[1] = TCPOLEN_MSS;
138 opt[2] = (newmss & 0xff00) >> 8;
139 opt[3] = newmss & 0x00ff;
140
141 inet_proto_csum_replace4(&tcph->check,
142
143 oldval = ((__be16 *)tcph)[6];
144 tcph->doff += TCPOLEN_MSS/4;
145 inet_proto_csum_replace2(&tcph->check,
146 oldval, ((__b
147 return TCPOLEN_MSS;
148 }
149
150 static u_int32_t tcpmss_reverse_mtu4(const str
151 {
152 struct flowi fl = {
153 .fl4_dst = iph->saddr,
154 };
155 const struct nf_afinfo *ai;
156 struct rtable *rt = NULL;
157 u_int32_t mtu = ~0U;
158
159 rcu_read_lock();
160 ai = nf_get_afinfo(AF_INET);
161 if (ai != NULL)
162 ai->route((struct dst_entry **
163 rcu_read_unlock();
164
165 if (rt != NULL) {
166 mtu = dst_mtu(&rt->u.dst);
167 dst_release(&rt->u.dst);
168 }
169 return mtu;
170 }
171
172 static unsigned int
173 tcpmss_tg4(struct sk_buff *skb, const struct n
174 const struct net_device *out, unsig
175 const struct xt_target *target, con
176 {
177 struct iphdr *iph = ip_hdr(skb);
178 __be16 newlen;
179 int ret;
180
181 ret = tcpmss_mangle_packet(skb, targin
182 iph->ihl *
183 sizeof(*iph
184 if (ret < 0)
185 return NF_DROP;
186 if (ret > 0) {
187 iph = ip_hdr(skb);
188 newlen = htons(ntohs(iph->tot_
189 csum_replace2(&iph->check, iph
190 iph->tot_len = newlen;
191 }
192 return XT_CONTINUE;
193 }
194
195 #if defined(CONFIG_IP6_NF_IPTABLES) || defined
196 static u_int32_t tcpmss_reverse_mtu6(const str
197 {
198 struct flowi fl = {
199 .fl6_dst = iph->saddr,
200 };
201 const struct nf_afinfo *ai;
202 struct rtable *rt = NULL;
203 u_int32_t mtu = ~0U;
204
205 rcu_read_lock();
206 ai = nf_get_afinfo(AF_INET6);
207 if (ai != NULL)
208 ai->route((struct dst_entry **
209 rcu_read_unlock();
210
211 if (rt != NULL) {
212 mtu = dst_mtu(&rt->u.dst);
213 dst_release(&rt->u.dst);
214 }
215 return mtu;
216 }
217
218 static unsigned int
219 tcpmss_tg6(struct sk_buff *skb, const struct n
220 const struct net_device *out, unsig
221 const struct xt_target *target, con
222 {
223 struct ipv6hdr *ipv6h = ipv6_hdr(skb);
224 u8 nexthdr;
225 int tcphoff;
226 int ret;
227
228 nexthdr = ipv6h->nexthdr;
229 tcphoff = ipv6_skip_exthdr(skb, sizeof
230 if (tcphoff < 0)
231 return NF_DROP;
232 ret = tcpmss_mangle_packet(skb, targin
233 tcphoff,
234 sizeof(*ipv
235 if (ret < 0)
236 return NF_DROP;
237 if (ret > 0) {
238 ipv6h = ipv6_hdr(skb);
239 ipv6h->payload_len = htons(nto
240 }
241 return XT_CONTINUE;
242 }
243 #endif
244
245 #define TH_SYN 0x02
246
247 /* Must specify -p tcp --syn */
248 static inline bool find_syn_match(const struct
249 {
250 const struct xt_tcp *tcpinfo = (const
251
252 if (strcmp(m->u.kernel.match->name, "t
253 tcpinfo->flg_cmp & TH_SYN &&
254 !(tcpinfo->invflags & XT_TCP_INV_F
255 return true;
256
257 return false;
258 }
259
260 static bool
261 tcpmss_tg4_check(const char *tablename, const
262 const struct xt_target *targe
263 unsigned int hook_mask)
264 {
265 const struct xt_tcpmss_info *info = ta
266 const struct ipt_entry *e = entry;
267
268 if (info->mss == XT_TCPMSS_CLAMP_PMTU
269 (hook_mask & ~((1 << NF_INET_FORWA
270 (1 << NF_INET_LOCAL
271 (1 << NF_INET_POST_
272 printk("xt_TCPMSS: path-MTU cl
273 "FORWARD, OUTPUT and PO
274 return false;
275 }
276 if (IPT_MATCH_ITERATE(e, find_syn_matc
277 return true;
278 printk("xt_TCPMSS: Only works on TCP S
279 return false;
280 }
281
282 #if defined(CONFIG_IP6_NF_IPTABLES) || defined
283 static bool
284 tcpmss_tg6_check(const char *tablename, const
285 const struct xt_target *targe
286 unsigned int hook_mask)
287 {
288 const struct xt_tcpmss_info *info = ta
289 const struct ip6t_entry *e = entry;
290
291 if (info->mss == XT_TCPMSS_CLAMP_PMTU
292 (hook_mask & ~((1 << NF_INET_FORWA
293 (1 << NF_INET_LOCAL
294 (1 << NF_INET_POST_
295 printk("xt_TCPMSS: path-MTU cl
296 "FORWARD, OUTPUT and PO
297 return false;
298 }
299 if (IP6T_MATCH_ITERATE(e, find_syn_mat
300 return true;
301 printk("xt_TCPMSS: Only works on TCP S
302 return false;
303 }
304 #endif
305
306 static struct xt_target tcpmss_tg_reg[] __read
307 {
308 .family = AF_INET,
309 .name = "TCPMSS",
310 .checkentry = tcpmss_tg4_c
311 .target = tcpmss_tg4,
312 .targetsize = sizeof(struc
313 .proto = IPPROTO_TCP,
314 .me = THIS_MODULE,
315 },
316 #if defined(CONFIG_IP6_NF_IPTABLES) || defined
317 {
318 .family = AF_INET6,
319 .name = "TCPMSS",
320 .checkentry = tcpmss_tg6_c
321 .target = tcpmss_tg6,
322 .targetsize = sizeof(struc
323 .proto = IPPROTO_TCP,
324 .me = THIS_MODULE,
325 },
326 #endif
327 };
328
329 static int __init tcpmss_tg_init(void)
330 {
331 return xt_register_targets(tcpmss_tg_r
332 }
333
334 static void __exit tcpmss_tg_exit(void)
335 {
336 xt_unregister_targets(tcpmss_tg_reg, A
337 }
338
339 module_init(tcpmss_tg_init);
340 module_exit(tcpmss_tg_exit);
341
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