[IP6TUNNEL]: Use proper net in hash-lookup functions.
[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/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 Segment Size (MSS) adjustment");
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 offset)
36 {
37         /* Beware zero-length options: make finite progress */
38         if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0)
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_info *info,
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_header(skb) + tcphoff);
62
63         /* Since it passed flags test in tcp match, we know it is is
64            not a fragment, and has data >= tcp header length.  SYN
65            packets should not contain data: if they did, then we risk
66            running over MTU, sending Frag Needed and breaking things
67            badly. --RR */
68         if (tcplen != tcph->doff*4) {
69                 if (net_ratelimit())
70                         printk(KERN_ERR "xt_TCPMSS: bad length (%u bytes)\n",
71                                skb->len);
72                 return -1;
73         }
74
75         if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
76                 if (dst_mtu(skb->dst) <= minlen) {
77                         if (net_ratelimit())
78                                 printk(KERN_ERR "xt_TCPMSS: "
79                                        "unknown or invalid path-MTU (%u)\n",
80                                        dst_mtu(skb->dst));
81                         return -1;
82                 }
83                 if (in_mtu <= minlen) {
84                         if (net_ratelimit())
85                                 printk(KERN_ERR "xt_TCPMSS: unknown or "
86                                        "invalid path-MTU (%u)\n", in_mtu);
87                         return -1;
88                 }
89                 newmss = min(dst_mtu(skb->dst), in_mtu) - minlen;
90         } else
91                 newmss = info->mss;
92
93         opt = (u_int8_t *)tcph;
94         for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) {
95                 if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS &&
96                     opt[i+1] == TCPOLEN_MSS) {
97                         u_int16_t oldmss;
98
99                         oldmss = (opt[i+2] << 8) | opt[i+3];
100
101                         /* Never increase MSS, even when setting it, as
102                          * doing so results in problems for hosts that rely
103                          * on MSS being set correctly.
104                          */
105                         if (oldmss <= newmss)
106                                 return 0;
107
108                         opt[i+2] = (newmss & 0xff00) >> 8;
109                         opt[i+3] = newmss & 0x00ff;
110
111                         inet_proto_csum_replace2(&tcph->check, skb,
112                                                  htons(oldmss), htons(newmss),
113                                                  0);
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_MSS - skb_tailroom(skb),
124                                      GFP_ATOMIC))
125                         return -1;
126                 tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
127         }
128
129         skb_put(skb, TCPOLEN_MSS);
130
131         opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
132         memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
133
134         inet_proto_csum_replace2(&tcph->check, skb,
135                                  htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
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, skb, 0, *((__be32 *)opt), 0);
142
143         oldval = ((__be16 *)tcph)[6];
144         tcph->doff += TCPOLEN_MSS/4;
145         inet_proto_csum_replace2(&tcph->check, skb,
146                                  oldval, ((__be16 *)tcph)[6], 0);
147         return TCPOLEN_MSS;
148 }
149
150 static u_int32_t tcpmss_reverse_mtu4(const struct iphdr *iph)
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 **)&rt, &fl);
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 net_device *in,
174            const struct net_device *out, unsigned int hooknum,
175            const struct xt_target *target, const void *targinfo)
176 {
177         struct iphdr *iph = ip_hdr(skb);
178         __be16 newlen;
179         int ret;
180
181         ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu4(iph),
182                                    iph->ihl * 4,
183                                    sizeof(*iph) + sizeof(struct tcphdr));
184         if (ret < 0)
185                 return NF_DROP;
186         if (ret > 0) {
187                 iph = ip_hdr(skb);
188                 newlen = htons(ntohs(iph->tot_len) + ret);
189                 csum_replace2(&iph->check, iph->tot_len, newlen);
190                 iph->tot_len = newlen;
191         }
192         return XT_CONTINUE;
193 }
194
195 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
196 static u_int32_t tcpmss_reverse_mtu6(const struct ipv6hdr *iph)
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 **)&rt, &fl);
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 net_device *in,
220            const struct net_device *out, unsigned int hooknum,
221            const struct xt_target *target, const void *targinfo)
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(*ipv6h), &nexthdr);
230         if (tcphoff < 0)
231                 return NF_DROP;
232         ret = tcpmss_mangle_packet(skb, targinfo, tcpmss_reverse_mtu6(ipv6h),
233                                    tcphoff,
234                                    sizeof(*ipv6h) + sizeof(struct tcphdr));
235         if (ret < 0)
236                 return NF_DROP;
237         if (ret > 0) {
238                 ipv6h = ipv6_hdr(skb);
239                 ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
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 xt_entry_match *m)
249 {
250         const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;
251
252         if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
253             tcpinfo->flg_cmp & TH_SYN &&
254             !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
255                 return true;
256
257         return false;
258 }
259
260 static bool
261 tcpmss_tg4_check(const char *tablename, const void *entry,
262                  const struct xt_target *target, void *targinfo,
263                  unsigned int hook_mask)
264 {
265         const struct xt_tcpmss_info *info = targinfo;
266         const struct ipt_entry *e = entry;
267
268         if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
269             (hook_mask & ~((1 << NF_INET_FORWARD) |
270                            (1 << NF_INET_LOCAL_OUT) |
271                            (1 << NF_INET_POST_ROUTING))) != 0) {
272                 printk("xt_TCPMSS: path-MTU clamping only supported in "
273                        "FORWARD, OUTPUT and POSTROUTING hooks\n");
274                 return false;
275         }
276         if (IPT_MATCH_ITERATE(e, find_syn_match))
277                 return true;
278         printk("xt_TCPMSS: Only works on TCP SYN packets\n");
279         return false;
280 }
281
282 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
283 static bool
284 tcpmss_tg6_check(const char *tablename, const void *entry,
285                  const struct xt_target *target, void *targinfo,
286                  unsigned int hook_mask)
287 {
288         const struct xt_tcpmss_info *info = targinfo;
289         const struct ip6t_entry *e = entry;
290
291         if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
292             (hook_mask & ~((1 << NF_INET_FORWARD) |
293                            (1 << NF_INET_LOCAL_OUT) |
294                            (1 << NF_INET_POST_ROUTING))) != 0) {
295                 printk("xt_TCPMSS: path-MTU clamping only supported in "
296                        "FORWARD, OUTPUT and POSTROUTING hooks\n");
297                 return false;
298         }
299         if (IP6T_MATCH_ITERATE(e, find_syn_match))
300                 return true;
301         printk("xt_TCPMSS: Only works on TCP SYN packets\n");
302         return false;
303 }
304 #endif
305
306 static struct xt_target tcpmss_tg_reg[] __read_mostly = {
307         {
308                 .family         = AF_INET,
309                 .name           = "TCPMSS",
310                 .checkentry     = tcpmss_tg4_check,
311                 .target         = tcpmss_tg4,
312                 .targetsize     = sizeof(struct xt_tcpmss_info),
313                 .proto          = IPPROTO_TCP,
314                 .me             = THIS_MODULE,
315         },
316 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
317         {
318                 .family         = AF_INET6,
319                 .name           = "TCPMSS",
320                 .checkentry     = tcpmss_tg6_check,
321                 .target         = tcpmss_tg6,
322                 .targetsize     = sizeof(struct xt_tcpmss_info),
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_reg, ARRAY_SIZE(tcpmss_tg_reg));
332 }
333
334 static void __exit tcpmss_tg_exit(void)
335 {
336         xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
337 }
338
339 module_init(tcpmss_tg_init);
340 module_exit(tcpmss_tg_exit);