[IPv6] RAW: Compact the API for the kernel
[linux-2.6] / net / netfilter / xt_TCPMSS.c
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 *skb,
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(skb, skb->len))
54                 return -1;
55
56         tcplen = skb->len - tcphoff;
57         tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
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                                skb->len);
68                 return -1;
69         }
70
71         if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
72                 if (dst_mtu(skb->dst) <= minlen) {
73                         if (net_ratelimit())
74                                 printk(KERN_ERR "xt_TCPMSS: "
75                                        "unknown or invalid path-MTU (%u)\n",
76                                        dst_mtu(skb->dst));
77                         return -1;
78                 }
79                 newmss = dst_mtu(skb->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, skb,
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(skb) < TCPOLEN_MSS) {
108                 if (pskb_expand_head(skb, 0,
109                                      TCPOLEN_MSS - skb_tailroom(skb),
110                                      GFP_ATOMIC))
111                         return -1;
112                 tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
113         }
114
115         skb_put(skb, 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, skb,
121                                htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
122         opt[0] = TCPOPT_MSS;
123         opt[1] = TCPOLEN_MSS;
124         opt[2] = (newmss & 0xff00) >> 8;
125         opt[3] = newmss & 0x00ff;
126
127         nf_proto_csum_replace4(&tcph->check, skb, 0, *((__be32 *)opt), 0);
128
129         oldval = ((__be16 *)tcph)[6];
130         tcph->doff += TCPOLEN_MSS/4;
131         nf_proto_csum_replace2(&tcph->check, skb,
132                                 oldval, ((__be16 *)tcph)[6], 0);
133         return TCPOLEN_MSS;
134 }
135
136 static unsigned int
137 xt_tcpmss_target4(struct sk_buff *skb,
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 {
144         struct iphdr *iph = ip_hdr(skb);
145         __be16 newlen;
146         int ret;
147
148         ret = tcpmss_mangle_packet(skb, targinfo, iph->ihl * 4,
149                                    sizeof(*iph) + sizeof(struct tcphdr));
150         if (ret < 0)
151                 return NF_DROP;
152         if (ret > 0) {
153                 iph = ip_hdr(skb);
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 *skb,
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 {
170         struct ipv6hdr *ipv6h = ipv6_hdr(skb);
171         u8 nexthdr;
172         int tcphoff;
173         int ret;
174
175         nexthdr = ipv6h->nexthdr;
176         tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr);
177         if (tcphoff < 0)
178                 return NF_DROP;
179         ret = tcpmss_mangle_packet(skb, targinfo, tcphoff,
180                                    sizeof(*ipv6h) + sizeof(struct tcphdr));
181         if (ret < 0)
182                 return NF_DROP;
183         if (ret > 0) {
184                 ipv6h = ipv6_hdr(skb);
185                 ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
186         }
187         return XT_CONTINUE;
188 }
189 #endif
190
191 #define TH_SYN 0x02
192
193 /* Must specify -p tcp --syn */
194 static inline bool find_syn_match(const struct xt_entry_match *m)
195 {
196         const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;
197
198         if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
199             tcpinfo->flg_cmp & TH_SYN &&
200             !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
201                 return true;
202
203         return false;
204 }
205
206 static bool
207 xt_tcpmss_checkentry4(const char *tablename,
208                       const void *entry,
209                       const struct xt_target *target,
210                       void *targinfo,
211                       unsigned int hook_mask)
212 {
213         const struct xt_tcpmss_info *info = targinfo;
214         const struct ipt_entry *e = entry;
215
216         if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
217             (hook_mask & ~((1 << NF_INET_FORWARD) |
218                            (1 << NF_INET_LOCAL_OUT) |
219                            (1 << NF_INET_POST_ROUTING))) != 0) {
220                 printk("xt_TCPMSS: path-MTU clamping only supported in "
221                        "FORWARD, OUTPUT and POSTROUTING hooks\n");
222                 return false;
223         }
224         if (IPT_MATCH_ITERATE(e, find_syn_match))
225                 return true;
226         printk("xt_TCPMSS: Only works on TCP SYN packets\n");
227         return false;
228 }
229
230 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
231 static bool
232 xt_tcpmss_checkentry6(const char *tablename,
233                       const void *entry,
234                       const struct xt_target *target,
235                       void *targinfo,
236                       unsigned int hook_mask)
237 {
238         const struct xt_tcpmss_info *info = targinfo;
239         const struct ip6t_entry *e = entry;
240
241         if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
242             (hook_mask & ~((1 << NF_INET_FORWARD) |
243                            (1 << NF_INET_LOCAL_OUT) |
244                            (1 << NF_INET_POST_ROUTING))) != 0) {
245                 printk("xt_TCPMSS: path-MTU clamping only supported in "
246                        "FORWARD, OUTPUT and POSTROUTING hooks\n");
247                 return false;
248         }
249         if (IP6T_MATCH_ITERATE(e, find_syn_match))
250                 return true;
251         printk("xt_TCPMSS: Only works on TCP SYN packets\n");
252         return false;
253 }
254 #endif
255
256 static struct xt_target xt_tcpmss_reg[] __read_mostly = {
257         {
258                 .family         = AF_INET,
259                 .name           = "TCPMSS",
260                 .checkentry     = xt_tcpmss_checkentry4,
261                 .target         = xt_tcpmss_target4,
262                 .targetsize     = sizeof(struct xt_tcpmss_info),
263                 .proto          = IPPROTO_TCP,
264                 .me             = THIS_MODULE,
265         },
266 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
267         {
268                 .family         = AF_INET6,
269                 .name           = "TCPMSS",
270                 .checkentry     = xt_tcpmss_checkentry6,
271                 .target         = xt_tcpmss_target6,
272                 .targetsize     = sizeof(struct xt_tcpmss_info),
273                 .proto          = IPPROTO_TCP,
274                 .me             = THIS_MODULE,
275         },
276 #endif
277 };
278
279 static int __init xt_tcpmss_init(void)
280 {
281         return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
282 }
283
284 static void __exit xt_tcpmss_fini(void)
285 {
286         xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
287 }
288
289 module_init(xt_tcpmss_init);
290 module_exit(xt_tcpmss_fini);