2 * Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net>
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, see <http://www.gnu.org/licenses/>.
18 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
19 #include <linux/module.h>
20 #include <linux/kernel.h>
22 #include <linux/capability.h>
24 #include <linux/inetdevice.h>
26 #include <linux/list.h>
27 #include <linux/rculist.h>
28 #include <linux/skbuff.h>
29 #include <linux/slab.h>
30 #include <linux/tcp.h>
35 #include <linux/netfilter/nfnetlink.h>
36 #include <linux/netfilter/x_tables.h>
37 #include <net/netfilter/nf_log.h>
38 #include <linux/netfilter/xt_osf.h>
40 struct xt_osf_finger {
41 struct rcu_head rcu_head;
42 struct list_head finger_entry;
43 struct xt_osf_user_finger finger;
46 enum osf_fmatch_states {
47 /* Packet does not match the fingerprint */
49 /* Packet matches the fingerprint */
51 /* Options do not match the fingerprint, but header does */
56 * Indexed by dont-fragment bit.
57 * It is the only constant value in the fingerprint.
59 static struct list_head xt_osf_fingers[2];
61 static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
62 [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) },
65 static int xt_osf_add_callback(struct net *net, struct sock *ctnl,
66 struct sk_buff *skb, const struct nlmsghdr *nlh,
67 const struct nlattr * const osf_attrs[])
69 struct xt_osf_user_finger *f;
70 struct xt_osf_finger *kf = NULL, *sf;
73 if (!capable(CAP_NET_ADMIN))
76 if (!osf_attrs[OSF_ATTR_FINGER])
79 if (!(nlh->nlmsg_flags & NLM_F_CREATE))
82 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
84 kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
88 memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
90 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
91 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
97 if (nlh->nlmsg_flags & NLM_F_EXCL)
103 * We are protected by nfnl mutex.
106 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
111 static int xt_osf_remove_callback(struct net *net, struct sock *ctnl,
113 const struct nlmsghdr *nlh,
114 const struct nlattr * const osf_attrs[])
116 struct xt_osf_user_finger *f;
117 struct xt_osf_finger *sf;
120 if (!capable(CAP_NET_ADMIN))
123 if (!osf_attrs[OSF_ATTR_FINGER])
126 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
128 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
129 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
133 * We are protected by nfnl mutex.
135 list_del_rcu(&sf->finger_entry);
136 kfree_rcu(sf, rcu_head);
145 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
147 .call = xt_osf_add_callback,
148 .attr_count = OSF_ATTR_MAX,
149 .policy = xt_osf_policy,
152 .call = xt_osf_remove_callback,
153 .attr_count = OSF_ATTR_MAX,
154 .policy = xt_osf_policy,
158 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
160 .subsys_id = NFNL_SUBSYS_OSF,
161 .cb_count = OSF_MSG_MAX,
162 .cb = xt_osf_nfnetlink_callbacks,
165 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
168 const struct iphdr *ip = ip_hdr(skb);
170 if (info->flags & XT_OSF_TTL) {
171 if (info->ttl == XT_OSF_TTL_TRUE)
172 return ip->ttl == f_ttl;
173 if (info->ttl == XT_OSF_TTL_NOCHECK)
175 else if (ip->ttl <= f_ttl)
178 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
182 if (inet_ifa_match(ip->saddr, ifa)) {
183 ret = (ip->ttl == f_ttl);
193 return ip->ttl == f_ttl;
197 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
199 const struct xt_osf_info *info = p->matchinfo;
200 const struct iphdr *ip = ip_hdr(skb);
201 const struct tcphdr *tcp;
203 int fmatch = FMATCH_WRONG, fcount = 0;
204 unsigned int optsize = 0, check_WSS = 0;
205 u16 window, totlen, mss = 0;
207 const unsigned char *optp = NULL, *_optp = NULL;
208 unsigned char opts[MAX_IPOPTLEN];
209 const struct xt_osf_finger *kf;
210 const struct xt_osf_user_finger *f;
211 struct net *net = p->net;
216 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
223 totlen = ntohs(ip->tot_len);
224 df = ntohs(ip->frag_off) & IP_DF;
225 window = ntohs(tcp->window);
227 if (tcp->doff * 4 > sizeof(struct tcphdr)) {
228 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
230 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
231 sizeof(struct tcphdr), optsize, opts);
235 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
236 int foptsize, optnum;
240 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
244 fmatch = FMATCH_WRONG;
246 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
250 * Should not happen if userspace parser was written correctly.
252 if (f->wss.wc >= OSF_WSS_MAX)
258 for (optnum = 0; optnum < f->opt_num; ++optnum)
259 foptsize += f->opt[optnum].length;
261 if (foptsize > MAX_IPOPTLEN ||
262 optsize > MAX_IPOPTLEN ||
266 check_WSS = f->wss.wc;
268 for (optnum = 0; optnum < f->opt_num; ++optnum) {
269 if (f->opt[optnum].kind == (*optp)) {
270 __u32 len = f->opt[optnum].length;
271 const __u8 *optend = optp + len;
281 mss = ntohs((__force __be16)mss);
289 fmatch = FMATCH_OPT_WRONG;
291 if (fmatch != FMATCH_OK)
295 if (fmatch != FMATCH_OPT_WRONG) {
296 fmatch = FMATCH_WRONG;
300 if (f->wss.val == 0 || window == f->wss.val)
305 * Some smart modems decrease mangle MSS to
306 * SMART_MSS_2, so we check standard, decreased
307 * and the one provided in the fingerprint MSS
310 #define SMART_MSS_1 1460
311 #define SMART_MSS_2 1448
312 if (window == f->wss.val * mss ||
313 window == f->wss.val * SMART_MSS_1 ||
314 window == f->wss.val * SMART_MSS_2)
318 if (window == f->wss.val * (mss + 40) ||
319 window == f->wss.val * (SMART_MSS_1 + 40) ||
320 window == f->wss.val * (SMART_MSS_2 + 40))
324 if ((window % f->wss.val) == 0)
330 if (fmatch != FMATCH_OK)
335 if (info->flags & XT_OSF_LOG)
336 nf_log_packet(net, p->family, p->hooknum, skb,
338 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
339 f->genre, f->version, f->subtype,
340 &ip->saddr, ntohs(tcp->source),
341 &ip->daddr, ntohs(tcp->dest),
344 if ((info->flags & XT_OSF_LOG) &&
345 info->loglevel == XT_OSF_LOGLEVEL_FIRST)
350 if (!fcount && (info->flags & XT_OSF_LOG))
351 nf_log_packet(net, p->family, p->hooknum, skb, p->in,
353 "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
354 &ip->saddr, ntohs(tcp->source),
355 &ip->daddr, ntohs(tcp->dest));
360 return fmatch == FMATCH_OK;
363 static struct xt_match xt_osf_match = {
366 .family = NFPROTO_IPV4,
367 .proto = IPPROTO_TCP,
368 .hooks = (1 << NF_INET_LOCAL_IN) |
369 (1 << NF_INET_PRE_ROUTING) |
370 (1 << NF_INET_FORWARD),
371 .match = xt_osf_match_packet,
372 .matchsize = sizeof(struct xt_osf_info),
376 static int __init xt_osf_init(void)
381 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
382 INIT_LIST_HEAD(&xt_osf_fingers[i]);
384 err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
386 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
390 err = xt_register_match(&xt_osf_match);
392 pr_err("Failed to register OS fingerprint "
393 "matching module (%d)\n", err);
400 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
405 static void __exit xt_osf_fini(void)
407 struct xt_osf_finger *f;
410 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
411 xt_unregister_match(&xt_osf_match);
414 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
416 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
417 list_del_rcu(&f->finger_entry);
418 kfree_rcu(f, rcu_head);
426 module_init(xt_osf_init);
427 module_exit(xt_osf_fini);
429 MODULE_LICENSE("GPL");
430 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
431 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
432 MODULE_ALIAS("ipt_osf");
433 MODULE_ALIAS("ip6t_osf");
434 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);