xref: /openbmc/linux/net/netfilter/nfnetlink_osf.c (revision 26ba4e57) 
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(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(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))
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 {
170 	const struct tcphdr *tcp;
171 	struct tcphdr _tcph;
172 
173 	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_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, ip_hdrlen(skb) +
188 				sizeof(struct tcphdr), ctx->optsize, opts);
189 	}
190 
191 	return tcp;
192 }
193 
194 bool
195 nf_osf_match(const struct sk_buff *skb, u_int8_t family,
196 	     int hooknum, struct net_device *in, struct net_device *out,
197 	     const struct nf_osf_info *info, struct net *net,
198 	     const struct list_head *nf_osf_fingers)
199 {
200 	const struct iphdr *ip = ip_hdr(skb);
201 	const struct nf_osf_user_finger *f;
202 	unsigned char opts[MAX_IPOPTLEN];
203 	const struct nf_osf_finger *kf;
204 	int fcount = 0, ttl_check;
205 	int fmatch = FMATCH_WRONG;
206 	struct nf_osf_hdr_ctx ctx;
207 	const struct tcphdr *tcp;
208 
209 	memset(&ctx, 0, sizeof(ctx));
210 
211 	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
212 	if (!tcp)
213 		return false;
214 
215 	ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
216 
217 	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
218 
219 		f = &kf->finger;
220 
221 		if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
222 			continue;
223 
224 		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
225 			continue;
226 
227 		fmatch = FMATCH_OK;
228 
229 		fcount++;
230 
231 		if (info->flags & NF_OSF_LOG)
232 			nf_log_packet(net, family, hooknum, skb,
233 				      in, out, NULL,
234 				      "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
235 				      f->genre, f->version, f->subtype,
236 				      &ip->saddr, ntohs(tcp->source),
237 				      &ip->daddr, ntohs(tcp->dest),
238 				      f->ttl - ip->ttl);
239 
240 		if ((info->flags & NF_OSF_LOG) &&
241 		    info->loglevel == NF_OSF_LOGLEVEL_FIRST)
242 			break;
243 	}
244 
245 	if (!fcount && (info->flags & NF_OSF_LOG))
246 		nf_log_packet(net, family, hooknum, skb, in, out, NULL,
247 			      "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
248 			      &ip->saddr, ntohs(tcp->source),
249 			      &ip->daddr, ntohs(tcp->dest));
250 
251 	if (fcount)
252 		fmatch = FMATCH_OK;
253 
254 	return fmatch == FMATCH_OK;
255 }
256 EXPORT_SYMBOL_GPL(nf_osf_match);
257 
258 bool nf_osf_find(const struct sk_buff *skb,
259 		 const struct list_head *nf_osf_fingers,
260 		 const int ttl_check, struct nf_osf_data *data)
261 {
262 	const struct iphdr *ip = ip_hdr(skb);
263 	const struct nf_osf_user_finger *f;
264 	unsigned char opts[MAX_IPOPTLEN];
265 	const struct nf_osf_finger *kf;
266 	struct nf_osf_hdr_ctx ctx;
267 	const struct tcphdr *tcp;
268 
269 	memset(&ctx, 0, sizeof(ctx));
270 
271 	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
272 	if (!tcp)
273 		return false;
274 
275 	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
276 		f = &kf->finger;
277 		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
278 			continue;
279 
280 		data->genre = f->genre;
281 		data->version = f->version;
282 		break;
283 	}
284 
285 	return true;
286 }
287 EXPORT_SYMBOL_GPL(nf_osf_find);
288 
289 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
290 	[OSF_ATTR_FINGER]	= { .len = sizeof(struct nf_osf_user_finger) },
291 };
292 
293 static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
294 				 struct sk_buff *skb, const struct nlmsghdr *nlh,
295 				 const struct nlattr * const osf_attrs[],
296 				 struct netlink_ext_ack *extack)
297 {
298 	struct nf_osf_user_finger *f;
299 	struct nf_osf_finger *kf = NULL, *sf;
300 	int err = 0;
301 
302 	if (!capable(CAP_NET_ADMIN))
303 		return -EPERM;
304 
305 	if (!osf_attrs[OSF_ATTR_FINGER])
306 		return -EINVAL;
307 
308 	if (!(nlh->nlmsg_flags & NLM_F_CREATE))
309 		return -EINVAL;
310 
311 	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
312 
313 	kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
314 	if (!kf)
315 		return -ENOMEM;
316 
317 	memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
318 
319 	list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
320 		if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
321 			continue;
322 
323 		kfree(kf);
324 		kf = NULL;
325 
326 		if (nlh->nlmsg_flags & NLM_F_EXCL)
327 			err = -EEXIST;
328 		break;
329 	}
330 
331 	/*
332 	 * We are protected by nfnl mutex.
333 	 */
334 	if (kf)
335 		list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
336 
337 	return err;
338 }
339 
340 static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
341 				    struct sk_buff *skb,
342 				    const struct nlmsghdr *nlh,
343 				    const struct nlattr * const osf_attrs[],
344 				    struct netlink_ext_ack *extack)
345 {
346 	struct nf_osf_user_finger *f;
347 	struct nf_osf_finger *sf;
348 	int err = -ENOENT;
349 
350 	if (!capable(CAP_NET_ADMIN))
351 		return -EPERM;
352 
353 	if (!osf_attrs[OSF_ATTR_FINGER])
354 		return -EINVAL;
355 
356 	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
357 
358 	list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
359 		if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
360 			continue;
361 
362 		/*
363 		 * We are protected by nfnl mutex.
364 		 */
365 		list_del_rcu(&sf->finger_entry);
366 		kfree_rcu(sf, rcu_head);
367 
368 		err = 0;
369 		break;
370 	}
371 
372 	return err;
373 }
374 
375 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
376 	[OSF_MSG_ADD]	= {
377 		.call		= nfnl_osf_add_callback,
378 		.attr_count	= OSF_ATTR_MAX,
379 		.policy		= nfnl_osf_policy,
380 	},
381 	[OSF_MSG_REMOVE]	= {
382 		.call		= nfnl_osf_remove_callback,
383 		.attr_count	= OSF_ATTR_MAX,
384 		.policy		= nfnl_osf_policy,
385 	},
386 };
387 
388 static const struct nfnetlink_subsystem nfnl_osf_subsys = {
389 	.name			= "osf",
390 	.subsys_id		= NFNL_SUBSYS_OSF,
391 	.cb_count		= OSF_MSG_MAX,
392 	.cb			= nfnl_osf_callbacks,
393 };
394 
395 static int __init nfnl_osf_init(void)
396 {
397 	int err = -EINVAL;
398 	int i;
399 
400 	for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
401 		INIT_LIST_HEAD(&nf_osf_fingers[i]);
402 
403 	err = nfnetlink_subsys_register(&nfnl_osf_subsys);
404 	if (err < 0) {
405 		pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
406 		goto err_out_exit;
407 	}
408 	return 0;
409 
410 err_out_exit:
411 	return err;
412 }
413 
414 static void __exit nfnl_osf_fini(void)
415 {
416 	struct nf_osf_finger *f;
417 	int i;
418 
419 	nfnetlink_subsys_unregister(&nfnl_osf_subsys);
420 
421 	rcu_read_lock();
422 	for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
423 		list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
424 			list_del_rcu(&f->finger_entry);
425 			kfree_rcu(f, rcu_head);
426 		}
427 	}
428 	rcu_read_unlock();
429 
430 	rcu_barrier();
431 }
432 
433 module_init(nfnl_osf_init);
434 module_exit(nfnl_osf_fini);
435 
436 MODULE_LICENSE("GPL");
437