1 /*-
2 * Copyright (c) 2017 Yandex LLC
3 * Copyright (c) 2017 Andrey V. Elsukov <ae@FreeBSD.org>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "opt_inet.h"
29 #include "opt_inet6.h"
30
31 #include <sys/param.h>
32 #include <sys/systm.h>
33 #include <sys/errno.h>
34 #include <sys/kernel.h>
35 #include <sys/mbuf.h>
36 #include <sys/module.h>
37 #include <sys/socket.h>
38
39 #include <net/if.h>
40 #include <net/if_var.h>
41 #include <net/pfil.h>
42 #include <net/vnet.h>
43
44 #include <netinet/in.h>
45 #include <netinet/ip.h>
46 #include <netinet/ip_var.h>
47 #include <netinet/tcp.h>
48 #include <netinet/ip_fw.h>
49 #include <netinet/ip6.h>
50
51 #include <netpfil/ipfw/ip_fw_private.h>
52 #include <netpfil/ipfw/pmod/pmod.h>
53
54 #include <machine/in_cksum.h>
55
56 VNET_DEFINE_STATIC(uint32_t, tcpmod_setmss_eid) = 0;
57 #define V_tcpmod_setmss_eid VNET(tcpmod_setmss_eid)
58
59 static int
tcpmod_setmss(struct mbuf ** mp,struct tcphdr * tcp,int tlen,uint16_t mss,int * done)60 tcpmod_setmss(struct mbuf **mp, struct tcphdr *tcp, int tlen, uint16_t mss,
61 int *done)
62 {
63 struct mbuf *m;
64 u_char *cp;
65 int optlen, ret;
66 uint16_t oldmss, csum;
67
68 m = *mp;
69 ret = IP_FW_DENY;
70 if (m->m_len < m->m_pkthdr.len) {
71 /*
72 * We shouldn't have any data, IP packet contains only
73 * TCP header with options.
74 */
75 *mp = m = m_pullup(m, m->m_pkthdr.len);
76 if (m == NULL) {
77 *done = 1;
78 return (ret);
79 }
80 }
81 /* Parse TCP options. */
82 for (tlen -= sizeof(struct tcphdr), cp = (u_char *)(tcp + 1);
83 tlen > 0; tlen -= optlen, cp += optlen) {
84 if (cp[0] == TCPOPT_EOL)
85 break;
86 if (cp[0] == TCPOPT_NOP) {
87 optlen = 1;
88 continue;
89 }
90 if (tlen < 2)
91 break;
92 optlen = cp[1];
93 if (optlen < 2 || optlen > tlen)
94 break;
95 if (cp[0] == TCPOPT_MAXSEG) {
96 if (optlen != TCPOLEN_MAXSEG)
97 break;
98 ret = 0; /* report success */
99 bcopy(cp + 2, &oldmss, sizeof(oldmss));
100 /* Do not update lower MSS value */
101 if (ntohs(oldmss) <= ntohs(mss))
102 break;
103 bcopy(&mss, cp + 2, sizeof(mss));
104 /* Update checksum if it is not delayed. */
105 if ((m->m_pkthdr.csum_flags &
106 (CSUM_TCP | CSUM_TCP_IPV6)) == 0) {
107 bcopy(&tcp->th_sum, &csum, sizeof(csum));
108 csum = cksum_adjust(csum, oldmss, mss);
109 bcopy(&csum, &tcp->th_sum, sizeof(csum));
110 }
111 break;
112 }
113 }
114
115 return (ret);
116 }
117
118 #ifdef INET6
119 static int
tcpmod_ipv6_setmss(struct mbuf ** mp,uint16_t mss,int * done)120 tcpmod_ipv6_setmss(struct mbuf **mp, uint16_t mss, int *done)
121 {
122 struct ip6_hdr *ip6;
123 struct ip6_hbh *hbh;
124 struct tcphdr *tcp;
125 int hlen, plen, proto;
126
127 ip6 = mtod(*mp, struct ip6_hdr *);
128 hlen = sizeof(*ip6);
129 proto = ip6->ip6_nxt;
130 /*
131 * Skip IPv6 extension headers and get the TCP header.
132 * ipfw_chk() has already done this work. So we are sure that
133 * we will not do an access to the out of bounds. For this
134 * reason we skip some checks here.
135 */
136 while (proto == IPPROTO_HOPOPTS || proto == IPPROTO_ROUTING ||
137 proto == IPPROTO_DSTOPTS) {
138 hbh = mtodo(*mp, hlen);
139 proto = hbh->ip6h_nxt;
140 hlen += (hbh->ip6h_len + 1) << 3;
141 }
142 tcp = mtodo(*mp, hlen);
143 plen = (*mp)->m_pkthdr.len - hlen;
144 hlen = tcp->th_off << 2;
145 /* We must have TCP options and enough data in a packet. */
146 if (hlen <= sizeof(struct tcphdr) || hlen > plen)
147 return (IP_FW_DENY);
148 return (tcpmod_setmss(mp, tcp, hlen, mss, done));
149 }
150 #endif /* INET6 */
151
152 #ifdef INET
153 static int
tcpmod_ipv4_setmss(struct mbuf ** mp,uint16_t mss,int * done)154 tcpmod_ipv4_setmss(struct mbuf **mp, uint16_t mss, int *done)
155 {
156 struct tcphdr *tcp;
157 struct ip *ip;
158 int hlen, plen;
159
160 ip = mtod(*mp, struct ip *);
161 hlen = ip->ip_hl << 2;
162 tcp = mtodo(*mp, hlen);
163 plen = (*mp)->m_pkthdr.len - hlen;
164 hlen = tcp->th_off << 2;
165 /* We must have TCP options and enough data in a packet. */
166 if (hlen <= sizeof(struct tcphdr) || hlen > plen)
167 return (IP_FW_DENY);
168 return (tcpmod_setmss(mp, tcp, hlen, mss, done));
169 }
170 #endif /* INET */
171
172 /*
173 * ipfw external action handler.
174 */
175 static int
ipfw_tcpmod(struct ip_fw_chain * chain,struct ip_fw_args * args,ipfw_insn * cmd,int * done)176 ipfw_tcpmod(struct ip_fw_chain *chain, struct ip_fw_args *args,
177 ipfw_insn *cmd, int *done)
178 {
179 ipfw_insn *icmd;
180 int ret;
181
182 *done = 0; /* try next rule if not matched */
183 ret = IP_FW_DENY;
184 icmd = cmd + F_LEN(cmd);
185 if (cmd->opcode != O_EXTERNAL_ACTION ||
186 insntod(cmd, kidx)->kidx != V_tcpmod_setmss_eid ||
187 icmd->opcode != O_EXTERNAL_DATA ||
188 icmd->len != F_INSN_SIZE(ipfw_insn))
189 return (ret);
190
191 /*
192 * NOTE: ipfw_chk() can set f_id.proto from IPv6 fragment header,
193 * but f_id._flags can be filled only from real TCP header.
194 *
195 * NOTE: ipfw_chk() drops very short packets in the PULLUP_TO()
196 * macro. But we need to check that mbuf is contiguous more than
197 * IP+IP_options/IP_extensions+tcphdr length, because TCP header
198 * must have TCP options, and ipfw_chk() does PULLUP_TO() size of
199 * struct tcphdr.
200 *
201 * NOTE: we require only the presence of SYN flag. User should
202 * properly configure the rule to select the direction of packets,
203 * that should be modified.
204 */
205 if (args->f_id.proto != IPPROTO_TCP ||
206 (args->f_id._flags & TH_SYN) == 0)
207 return (ret);
208
209 switch (args->f_id.addr_type) {
210 #ifdef INET
211 case 4:
212 ret = tcpmod_ipv4_setmss(&args->m, htons(icmd->arg1),
213 done);
214 break;
215 #endif
216 #ifdef INET6
217 case 6:
218 ret = tcpmod_ipv6_setmss(&args->m, htons(icmd->arg1),
219 done);
220 break;
221 #endif
222 }
223 /*
224 * We return zero in both @ret and @done on success, and ipfw_chk()
225 * will update rule counters. Otherwise a packet will not be matched
226 * by rule. We passed @done around above in case we hit a fatal error
227 * somewhere, we'll return non-zero but signal that rule processing
228 * cannot succeed.
229 */
230 return (ret);
231 }
232
233 int
tcpmod_init(struct ip_fw_chain * ch,int first)234 tcpmod_init(struct ip_fw_chain *ch, int first)
235 {
236
237 V_tcpmod_setmss_eid = ipfw_add_eaction(ch, ipfw_tcpmod, "tcp-setmss");
238 if (V_tcpmod_setmss_eid == 0)
239 return (ENXIO);
240 return (0);
241 }
242
243 void
tcpmod_uninit(struct ip_fw_chain * ch,int last)244 tcpmod_uninit(struct ip_fw_chain *ch, int last)
245 {
246
247 ipfw_del_eaction(ch, V_tcpmod_setmss_eid);
248 V_tcpmod_setmss_eid = 0;
249 }
250