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, write to the Free Software
17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
19 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
20 #include <linux/module.h>
21 #include <linux/kernel.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 sock *ctnl, struct sk_buff *skb,
66 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 (!osf_attrs[OSF_ATTR_FINGER])
76 if (!(nlh->nlmsg_flags & NLM_F_CREATE))
79 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
81 kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
85 memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
87 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
88 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
94 if (nlh->nlmsg_flags & NLM_F_EXCL)
100 * We are protected by nfnl mutex.
103 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
108 static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
109 const struct nlmsghdr *nlh,
110 const struct nlattr * const osf_attrs[])
112 struct xt_osf_user_finger *f;
113 struct xt_osf_finger *sf;
116 if (!osf_attrs[OSF_ATTR_FINGER])
119 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
121 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
122 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
126 * We are protected by nfnl mutex.
128 list_del_rcu(&sf->finger_entry);
129 kfree_rcu(sf, rcu_head);
138 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
140 .call = xt_osf_add_callback,
141 .attr_count = OSF_ATTR_MAX,
142 .policy = xt_osf_policy,
145 .call = xt_osf_remove_callback,
146 .attr_count = OSF_ATTR_MAX,
147 .policy = xt_osf_policy,
151 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
153 .subsys_id = NFNL_SUBSYS_OSF,
154 .cb_count = OSF_MSG_MAX,
155 .cb = xt_osf_nfnetlink_callbacks,
158 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
161 const struct iphdr *ip = ip_hdr(skb);
163 if (info->flags & XT_OSF_TTL) {
164 if (info->ttl == XT_OSF_TTL_TRUE)
165 return ip->ttl == f_ttl;
166 if (info->ttl == XT_OSF_TTL_NOCHECK)
168 else if (ip->ttl <= f_ttl)
171 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
175 if (inet_ifa_match(ip->saddr, ifa)) {
176 ret = (ip->ttl == f_ttl);
186 return ip->ttl == f_ttl;
190 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
192 const struct xt_osf_info *info = p->matchinfo;
193 const struct iphdr *ip = ip_hdr(skb);
194 const struct tcphdr *tcp;
196 int fmatch = FMATCH_WRONG, fcount = 0;
197 unsigned int optsize = 0, check_WSS = 0;
198 u16 window, totlen, mss = 0;
200 const unsigned char *optp = NULL, *_optp = NULL;
201 unsigned char opts[MAX_IPOPTLEN];
202 const struct xt_osf_finger *kf;
203 const struct xt_osf_user_finger *f;
204 struct net *net = dev_net(p->in ? p->in : p->out);
209 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
216 totlen = ntohs(ip->tot_len);
217 df = ntohs(ip->frag_off) & IP_DF;
218 window = ntohs(tcp->window);
220 if (tcp->doff * 4 > sizeof(struct tcphdr)) {
221 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
223 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
224 sizeof(struct tcphdr), optsize, opts);
228 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
231 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
235 fmatch = FMATCH_WRONG;
237 if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) {
238 int foptsize, optnum;
241 * Should not happen if userspace parser was written correctly.
243 if (f->wss.wc >= OSF_WSS_MAX)
249 for (optnum = 0; optnum < f->opt_num; ++optnum)
250 foptsize += f->opt[optnum].length;
252 if (foptsize > MAX_IPOPTLEN ||
253 optsize > MAX_IPOPTLEN ||
257 check_WSS = f->wss.wc;
259 for (optnum = 0; optnum < f->opt_num; ++optnum) {
260 if (f->opt[optnum].kind == (*optp)) {
261 __u32 len = f->opt[optnum].length;
262 const __u8 *optend = optp + len;
273 mss = ntohs((__force __be16)mss);
282 fmatch = FMATCH_OPT_WRONG;
284 if (fmatch != FMATCH_OK)
288 if (fmatch != FMATCH_OPT_WRONG) {
289 fmatch = FMATCH_WRONG;
293 if (f->wss.val == 0 || window == f->wss.val)
298 * Some smart modems decrease mangle MSS to
299 * SMART_MSS_2, so we check standard, decreased
300 * and the one provided in the fingerprint MSS
303 #define SMART_MSS_1 1460
304 #define SMART_MSS_2 1448
305 if (window == f->wss.val * mss ||
306 window == f->wss.val * SMART_MSS_1 ||
307 window == f->wss.val * SMART_MSS_2)
311 if (window == f->wss.val * (mss + 40) ||
312 window == f->wss.val * (SMART_MSS_1 + 40) ||
313 window == f->wss.val * (SMART_MSS_2 + 40))
317 if ((window % f->wss.val) == 0)
323 if (fmatch != FMATCH_OK)
328 if (info->flags & XT_OSF_LOG)
329 nf_log_packet(net, p->family, p->hooknum, skb,
331 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
332 f->genre, f->version, f->subtype,
333 &ip->saddr, ntohs(tcp->source),
334 &ip->daddr, ntohs(tcp->dest),
337 if ((info->flags & XT_OSF_LOG) &&
338 info->loglevel == XT_OSF_LOGLEVEL_FIRST)
344 if (!fcount && (info->flags & XT_OSF_LOG))
345 nf_log_packet(net, p->family, p->hooknum, skb, p->in,
347 "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
348 &ip->saddr, ntohs(tcp->source),
349 &ip->daddr, ntohs(tcp->dest));
354 return fmatch == FMATCH_OK;
357 static struct xt_match xt_osf_match = {
360 .family = NFPROTO_IPV4,
361 .proto = IPPROTO_TCP,
362 .hooks = (1 << NF_INET_LOCAL_IN) |
363 (1 << NF_INET_PRE_ROUTING) |
364 (1 << NF_INET_FORWARD),
365 .match = xt_osf_match_packet,
366 .matchsize = sizeof(struct xt_osf_info),
370 static int __init xt_osf_init(void)
375 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
376 INIT_LIST_HEAD(&xt_osf_fingers[i]);
378 err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
380 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
384 err = xt_register_match(&xt_osf_match);
386 pr_err("Failed to register OS fingerprint "
387 "matching module (%d)\n", err);
394 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
399 static void __exit xt_osf_fini(void)
401 struct xt_osf_finger *f;
404 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
405 xt_unregister_match(&xt_osf_match);
408 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
410 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
411 list_del_rcu(&f->finger_entry);
412 kfree_rcu(f, rcu_head);
420 module_init(xt_osf_init);
421 module_exit(xt_osf_fini);
423 MODULE_LICENSE("GPL");
424 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
425 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
426 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);