1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
3 | #include <linux/module.h> |
4 | #include <linux/kernel.h> |
5 | |
6 | #include <linux/capability.h> |
7 | #include <linux/if.h> |
8 | #include <linux/inetdevice.h> |
9 | #include <linux/ip.h> |
10 | #include <linux/list.h> |
11 | #include <linux/rculist.h> |
12 | #include <linux/skbuff.h> |
13 | #include <linux/slab.h> |
14 | #include <linux/tcp.h> |
15 | |
16 | #include <net/ip.h> |
17 | #include <net/tcp.h> |
18 | |
19 | #include <linux/netfilter/nfnetlink.h> |
20 | #include <linux/netfilter/x_tables.h> |
21 | #include <net/netfilter/nf_log.h> |
22 | #include <linux/netfilter/nfnetlink_osf.h> |
23 | |
24 | /* |
25 | * Indexed by dont-fragment bit. |
26 | * It is the only constant value in the fingerprint. |
27 | */ |
28 | struct list_head nf_osf_fingers[2]; |
29 | EXPORT_SYMBOL_GPL(nf_osf_fingers); |
30 | |
31 | static inline int nf_osf_ttl(const struct sk_buff *skb, |
32 | int ttl_check, unsigned char f_ttl) |
33 | { |
34 | struct in_device *in_dev = __in_dev_get_rcu(dev: skb->dev); |
35 | const struct iphdr *ip = ip_hdr(skb); |
36 | const struct in_ifaddr *ifa; |
37 | int ret = 0; |
38 | |
39 | if (ttl_check == NF_OSF_TTL_TRUE) |
40 | return ip->ttl == f_ttl; |
41 | if (ttl_check == NF_OSF_TTL_NOCHECK) |
42 | return 1; |
43 | else if (ip->ttl <= f_ttl) |
44 | return 1; |
45 | |
46 | in_dev_for_each_ifa_rcu(ifa, in_dev) { |
47 | if (inet_ifa_match(addr: ip->saddr, ifa)) { |
48 | ret = (ip->ttl == f_ttl); |
49 | break; |
50 | } |
51 | } |
52 | |
53 | return ret; |
54 | } |
55 | |
56 | struct nf_osf_hdr_ctx { |
57 | bool df; |
58 | u16 window; |
59 | u16 totlen; |
60 | const unsigned char *optp; |
61 | unsigned int optsize; |
62 | }; |
63 | |
64 | static bool nf_osf_match_one(const struct sk_buff *skb, |
65 | const struct nf_osf_user_finger *f, |
66 | int ttl_check, |
67 | struct nf_osf_hdr_ctx *ctx) |
68 | { |
69 | const __u8 *optpinit = ctx->optp; |
70 | unsigned int check_WSS = 0; |
71 | int fmatch = FMATCH_WRONG; |
72 | int foptsize, optnum; |
73 | u16 mss = 0; |
74 | |
75 | if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f_ttl: f->ttl)) |
76 | return false; |
77 | |
78 | /* |
79 | * Should not happen if userspace parser was written correctly. |
80 | */ |
81 | if (f->wss.wc >= OSF_WSS_MAX) |
82 | return false; |
83 | |
84 | /* Check options */ |
85 | |
86 | foptsize = 0; |
87 | for (optnum = 0; optnum < f->opt_num; ++optnum) |
88 | foptsize += f->opt[optnum].length; |
89 | |
90 | if (foptsize > MAX_IPOPTLEN || |
91 | ctx->optsize > MAX_IPOPTLEN || |
92 | ctx->optsize != foptsize) |
93 | return false; |
94 | |
95 | check_WSS = f->wss.wc; |
96 | |
97 | for (optnum = 0; optnum < f->opt_num; ++optnum) { |
98 | if (f->opt[optnum].kind == *ctx->optp) { |
99 | __u32 len = f->opt[optnum].length; |
100 | const __u8 *optend = ctx->optp + len; |
101 | |
102 | fmatch = FMATCH_OK; |
103 | |
104 | switch (*ctx->optp) { |
105 | case OSFOPT_MSS: |
106 | mss = ctx->optp[3]; |
107 | mss <<= 8; |
108 | mss |= ctx->optp[2]; |
109 | |
110 | mss = ntohs((__force __be16)mss); |
111 | break; |
112 | case OSFOPT_TS: |
113 | break; |
114 | } |
115 | |
116 | ctx->optp = optend; |
117 | } else |
118 | fmatch = FMATCH_OPT_WRONG; |
119 | |
120 | if (fmatch != FMATCH_OK) |
121 | break; |
122 | } |
123 | |
124 | if (fmatch != FMATCH_OPT_WRONG) { |
125 | fmatch = FMATCH_WRONG; |
126 | |
127 | switch (check_WSS) { |
128 | case OSF_WSS_PLAIN: |
129 | if (f->wss.val == 0 || ctx->window == f->wss.val) |
130 | fmatch = FMATCH_OK; |
131 | break; |
132 | case OSF_WSS_MSS: |
133 | /* |
134 | * Some smart modems decrease mangle MSS to |
135 | * SMART_MSS_2, so we check standard, decreased |
136 | * and the one provided in the fingerprint MSS |
137 | * values. |
138 | */ |
139 | #define SMART_MSS_1 1460 |
140 | #define SMART_MSS_2 1448 |
141 | if (ctx->window == f->wss.val * mss || |
142 | ctx->window == f->wss.val * SMART_MSS_1 || |
143 | ctx->window == f->wss.val * SMART_MSS_2) |
144 | fmatch = FMATCH_OK; |
145 | break; |
146 | case OSF_WSS_MTU: |
147 | if (ctx->window == f->wss.val * (mss + 40) || |
148 | ctx->window == f->wss.val * (SMART_MSS_1 + 40) || |
149 | ctx->window == f->wss.val * (SMART_MSS_2 + 40)) |
150 | fmatch = FMATCH_OK; |
151 | break; |
152 | case OSF_WSS_MODULO: |
153 | if ((ctx->window % f->wss.val) == 0) |
154 | fmatch = FMATCH_OK; |
155 | break; |
156 | } |
157 | } |
158 | |
159 | if (fmatch != FMATCH_OK) |
160 | ctx->optp = optpinit; |
161 | |
162 | return fmatch == FMATCH_OK; |
163 | } |
164 | |
165 | static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx, |
166 | const struct sk_buff *skb, |
167 | const struct iphdr *ip, |
168 | unsigned char *opts, |
169 | struct tcphdr *_tcph) |
170 | { |
171 | const struct tcphdr *tcp; |
172 | |
173 | tcp = skb_header_pointer(skb, offset: ip_hdrlen(skb), len: sizeof(struct tcphdr), buffer: _tcph); |
174 | if (!tcp) |
175 | return NULL; |
176 | |
177 | if (!tcp->syn) |
178 | return NULL; |
179 | |
180 | ctx->totlen = ntohs(ip->tot_len); |
181 | ctx->df = ntohs(ip->frag_off) & IP_DF; |
182 | ctx->window = ntohs(tcp->window); |
183 | |
184 | if (tcp->doff * 4 > sizeof(struct tcphdr)) { |
185 | ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr); |
186 | |
187 | ctx->optp = skb_header_pointer(skb, offset: ip_hdrlen(skb) + |
188 | sizeof(struct tcphdr), len: ctx->optsize, buffer: opts); |
189 | if (!ctx->optp) |
190 | return NULL; |
191 | } |
192 | |
193 | return tcp; |
194 | } |
195 | |
196 | bool |
197 | nf_osf_match(const struct sk_buff *skb, u_int8_t family, |
198 | int hooknum, struct net_device *in, struct net_device *out, |
199 | const struct nf_osf_info *info, struct net *net, |
200 | const struct list_head *nf_osf_fingers) |
201 | { |
202 | const struct iphdr *ip = ip_hdr(skb); |
203 | const struct nf_osf_user_finger *f; |
204 | unsigned char opts[MAX_IPOPTLEN]; |
205 | const struct nf_osf_finger *kf; |
206 | int fcount = 0, ttl_check; |
207 | int fmatch = FMATCH_WRONG; |
208 | struct nf_osf_hdr_ctx ctx; |
209 | const struct tcphdr *tcp; |
210 | struct tcphdr _tcph; |
211 | |
212 | memset(&ctx, 0, sizeof(ctx)); |
213 | |
214 | tcp = nf_osf_hdr_ctx_init(ctx: &ctx, skb, ip, opts, tcph: &_tcph); |
215 | if (!tcp) |
216 | return false; |
217 | |
218 | ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0; |
219 | |
220 | list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { |
221 | |
222 | f = &kf->finger; |
223 | |
224 | if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre)) |
225 | continue; |
226 | |
227 | if (!nf_osf_match_one(skb, f, ttl_check, ctx: &ctx)) |
228 | continue; |
229 | |
230 | fmatch = FMATCH_OK; |
231 | |
232 | fcount++; |
233 | |
234 | if (info->flags & NF_OSF_LOG) |
235 | nf_log_packet(net, pf: family, hooknum, skb, |
236 | in, out, NULL, |
237 | fmt: "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n" , |
238 | f->genre, f->version, f->subtype, |
239 | &ip->saddr, ntohs(tcp->source), |
240 | &ip->daddr, ntohs(tcp->dest), |
241 | f->ttl - ip->ttl); |
242 | |
243 | if ((info->flags & NF_OSF_LOG) && |
244 | info->loglevel == NF_OSF_LOGLEVEL_FIRST) |
245 | break; |
246 | } |
247 | |
248 | if (!fcount && (info->flags & NF_OSF_LOG)) |
249 | nf_log_packet(net, pf: family, hooknum, skb, in, out, NULL, |
250 | fmt: "Remote OS is not known: %pI4:%u -> %pI4:%u\n" , |
251 | &ip->saddr, ntohs(tcp->source), |
252 | &ip->daddr, ntohs(tcp->dest)); |
253 | |
254 | if (fcount) |
255 | fmatch = FMATCH_OK; |
256 | |
257 | return fmatch == FMATCH_OK; |
258 | } |
259 | EXPORT_SYMBOL_GPL(nf_osf_match); |
260 | |
261 | bool nf_osf_find(const struct sk_buff *skb, |
262 | const struct list_head *nf_osf_fingers, |
263 | const int ttl_check, struct nf_osf_data *data) |
264 | { |
265 | const struct iphdr *ip = ip_hdr(skb); |
266 | const struct nf_osf_user_finger *f; |
267 | unsigned char opts[MAX_IPOPTLEN]; |
268 | const struct nf_osf_finger *kf; |
269 | struct nf_osf_hdr_ctx ctx; |
270 | const struct tcphdr *tcp; |
271 | struct tcphdr _tcph; |
272 | bool found = false; |
273 | |
274 | memset(&ctx, 0, sizeof(ctx)); |
275 | |
276 | tcp = nf_osf_hdr_ctx_init(ctx: &ctx, skb, ip, opts, tcph: &_tcph); |
277 | if (!tcp) |
278 | return false; |
279 | |
280 | list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { |
281 | f = &kf->finger; |
282 | if (!nf_osf_match_one(skb, f, ttl_check, ctx: &ctx)) |
283 | continue; |
284 | |
285 | data->genre = f->genre; |
286 | data->version = f->version; |
287 | found = true; |
288 | break; |
289 | } |
290 | |
291 | return found; |
292 | } |
293 | EXPORT_SYMBOL_GPL(nf_osf_find); |
294 | |
295 | static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = { |
296 | [OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) }, |
297 | }; |
298 | |
299 | static int nfnl_osf_add_callback(struct sk_buff *skb, |
300 | const struct nfnl_info *info, |
301 | const struct nlattr * const osf_attrs[]) |
302 | { |
303 | struct nf_osf_user_finger *f; |
304 | struct nf_osf_finger *kf = NULL, *sf; |
305 | int err = 0; |
306 | |
307 | if (!capable(CAP_NET_ADMIN)) |
308 | return -EPERM; |
309 | |
310 | if (!osf_attrs[OSF_ATTR_FINGER]) |
311 | return -EINVAL; |
312 | |
313 | if (!(info->nlh->nlmsg_flags & NLM_F_CREATE)) |
314 | return -EINVAL; |
315 | |
316 | f = nla_data(nla: osf_attrs[OSF_ATTR_FINGER]); |
317 | |
318 | if (f->opt_num > ARRAY_SIZE(f->opt)) |
319 | return -EINVAL; |
320 | |
321 | if (!memchr(p: f->genre, c: 0, MAXGENRELEN) || |
322 | !memchr(p: f->subtype, c: 0, MAXGENRELEN) || |
323 | !memchr(p: f->version, c: 0, MAXGENRELEN)) |
324 | return -EINVAL; |
325 | |
326 | kf = kmalloc(size: sizeof(struct nf_osf_finger), GFP_KERNEL); |
327 | if (!kf) |
328 | return -ENOMEM; |
329 | |
330 | memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger)); |
331 | |
332 | list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { |
333 | if (memcmp(p: &sf->finger, q: f, size: sizeof(struct nf_osf_user_finger))) |
334 | continue; |
335 | |
336 | kfree(objp: kf); |
337 | kf = NULL; |
338 | |
339 | if (info->nlh->nlmsg_flags & NLM_F_EXCL) |
340 | err = -EEXIST; |
341 | break; |
342 | } |
343 | |
344 | /* |
345 | * We are protected by nfnl mutex. |
346 | */ |
347 | if (kf) |
348 | list_add_tail_rcu(new: &kf->finger_entry, head: &nf_osf_fingers[!!f->df]); |
349 | |
350 | return err; |
351 | } |
352 | |
353 | static int nfnl_osf_remove_callback(struct sk_buff *skb, |
354 | const struct nfnl_info *info, |
355 | const struct nlattr * const osf_attrs[]) |
356 | { |
357 | struct nf_osf_user_finger *f; |
358 | struct nf_osf_finger *sf; |
359 | int err = -ENOENT; |
360 | |
361 | if (!capable(CAP_NET_ADMIN)) |
362 | return -EPERM; |
363 | |
364 | if (!osf_attrs[OSF_ATTR_FINGER]) |
365 | return -EINVAL; |
366 | |
367 | f = nla_data(nla: osf_attrs[OSF_ATTR_FINGER]); |
368 | |
369 | list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { |
370 | if (memcmp(p: &sf->finger, q: f, size: sizeof(struct nf_osf_user_finger))) |
371 | continue; |
372 | |
373 | /* |
374 | * We are protected by nfnl mutex. |
375 | */ |
376 | list_del_rcu(entry: &sf->finger_entry); |
377 | kfree_rcu(sf, rcu_head); |
378 | |
379 | err = 0; |
380 | break; |
381 | } |
382 | |
383 | return err; |
384 | } |
385 | |
386 | static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = { |
387 | [OSF_MSG_ADD] = { |
388 | .call = nfnl_osf_add_callback, |
389 | .type = NFNL_CB_MUTEX, |
390 | .attr_count = OSF_ATTR_MAX, |
391 | .policy = nfnl_osf_policy, |
392 | }, |
393 | [OSF_MSG_REMOVE] = { |
394 | .call = nfnl_osf_remove_callback, |
395 | .type = NFNL_CB_MUTEX, |
396 | .attr_count = OSF_ATTR_MAX, |
397 | .policy = nfnl_osf_policy, |
398 | }, |
399 | }; |
400 | |
401 | static const struct nfnetlink_subsystem nfnl_osf_subsys = { |
402 | .name = "osf" , |
403 | .subsys_id = NFNL_SUBSYS_OSF, |
404 | .cb_count = OSF_MSG_MAX, |
405 | .cb = nfnl_osf_callbacks, |
406 | }; |
407 | |
408 | static int __init nfnl_osf_init(void) |
409 | { |
410 | int err = -EINVAL; |
411 | int i; |
412 | |
413 | for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) |
414 | INIT_LIST_HEAD(list: &nf_osf_fingers[i]); |
415 | |
416 | err = nfnetlink_subsys_register(n: &nfnl_osf_subsys); |
417 | if (err < 0) { |
418 | pr_err("Failed to register OSF nsfnetlink helper (%d)\n" , err); |
419 | goto err_out_exit; |
420 | } |
421 | return 0; |
422 | |
423 | err_out_exit: |
424 | return err; |
425 | } |
426 | |
427 | static void __exit nfnl_osf_fini(void) |
428 | { |
429 | struct nf_osf_finger *f; |
430 | int i; |
431 | |
432 | nfnetlink_subsys_unregister(n: &nfnl_osf_subsys); |
433 | |
434 | rcu_read_lock(); |
435 | for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) { |
436 | list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) { |
437 | list_del_rcu(entry: &f->finger_entry); |
438 | kfree_rcu(f, rcu_head); |
439 | } |
440 | } |
441 | rcu_read_unlock(); |
442 | |
443 | rcu_barrier(); |
444 | } |
445 | |
446 | module_init(nfnl_osf_init); |
447 | module_exit(nfnl_osf_fini); |
448 | |
449 | MODULE_LICENSE("GPL" ); |
450 | MODULE_DESCRIPTION("Passive OS fingerprint matching" ); |
451 | MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); |
452 | |