xref: /openbmc/linux/net/netfilter/nfnetlink_osf.c (revision b7019ac5) 
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 	int ret = 0;
37 
38 	if (ttl_check == NF_OSF_TTL_TRUE)
39 		return ip->ttl == f_ttl;
40 	if (ttl_check == NF_OSF_TTL_NOCHECK)
41 		return 1;
42 	else if (ip->ttl <= f_ttl)
43 		return 1;
44 
45 	for_ifa(in_dev) {
46 		if (inet_ifa_match(ip->saddr, ifa)) {
47 			ret = (ip->ttl == f_ttl);
48 			break;
49 		}
50 	}
51 
52 	endfor_ifa(in_dev);
53 
54 	return ret;
55 }
56 
57 struct nf_osf_hdr_ctx {
58 	bool			df;
59 	u16			window;
60 	u16			totlen;
61 	const unsigned char	*optp;
62 	unsigned int		optsize;
63 };
64 
65 static bool nf_osf_match_one(const struct sk_buff *skb,
66 			     const struct nf_osf_user_finger *f,
67 			     int ttl_check,
68 			     struct nf_osf_hdr_ctx *ctx)
69 {
70 	const __u8 *optpinit = ctx->optp;
71 	unsigned int check_WSS = 0;
72 	int fmatch = FMATCH_WRONG;
73 	int foptsize, optnum;
74 	u16 mss = 0;
75 
76 	if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
77 		return false;
78 
79 	/*
80 	 * Should not happen if userspace parser was written correctly.
81 	 */
82 	if (f->wss.wc >= OSF_WSS_MAX)
83 		return false;
84 
85 	/* Check options */
86 
87 	foptsize = 0;
88 	for (optnum = 0; optnum < f->opt_num; ++optnum)
89 		foptsize += f->opt[optnum].length;
90 
91 	if (foptsize > MAX_IPOPTLEN ||
92 	    ctx->optsize > MAX_IPOPTLEN ||
93 	    ctx->optsize != foptsize)
94 		return false;
95 
96 	check_WSS = f->wss.wc;
97 
98 	for (optnum = 0; optnum < f->opt_num; ++optnum) {
99 		if (f->opt[optnum].kind == *ctx->optp) {
100 			__u32 len = f->opt[optnum].length;
101 			const __u8 *optend = ctx->optp + len;
102 
103 			fmatch = FMATCH_OK;
104 
105 			switch (*ctx->optp) {
106 			case OSFOPT_MSS:
107 				mss = ctx->optp[3];
108 				mss <<= 8;
109 				mss |= ctx->optp[2];
110 
111 				mss = ntohs((__force __be16)mss);
112 				break;
113 			case OSFOPT_TS:
114 				break;
115 			}
116 
117 			ctx->optp = optend;
118 		} else
119 			fmatch = FMATCH_OPT_WRONG;
120 
121 		if (fmatch != FMATCH_OK)
122 			break;
123 	}
124 
125 	if (fmatch != FMATCH_OPT_WRONG) {
126 		fmatch = FMATCH_WRONG;
127 
128 		switch (check_WSS) {
129 		case OSF_WSS_PLAIN:
130 			if (f->wss.val == 0 || ctx->window == f->wss.val)
131 				fmatch = FMATCH_OK;
132 			break;
133 		case OSF_WSS_MSS:
134 			/*
135 			 * Some smart modems decrease mangle MSS to
136 			 * SMART_MSS_2, so we check standard, decreased
137 			 * and the one provided in the fingerprint MSS
138 			 * values.
139 			 */
140 #define SMART_MSS_1	1460
141 #define SMART_MSS_2	1448
142 			if (ctx->window == f->wss.val * mss ||
143 			    ctx->window == f->wss.val * SMART_MSS_1 ||
144 			    ctx->window == f->wss.val * SMART_MSS_2)
145 				fmatch = FMATCH_OK;
146 			break;
147 		case OSF_WSS_MTU:
148 			if (ctx->window == f->wss.val * (mss + 40) ||
149 			    ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
150 			    ctx->window == f->wss.val * (SMART_MSS_2 + 40))
151 				fmatch = FMATCH_OK;
152 			break;
153 		case OSF_WSS_MODULO:
154 			if ((ctx->window % f->wss.val) == 0)
155 				fmatch = FMATCH_OK;
156 			break;
157 		}
158 	}
159 
160 	if (fmatch != FMATCH_OK)
161 		ctx->optp = optpinit;
162 
163 	return fmatch == FMATCH_OK;
164 }
165 
166 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
167 						const struct sk_buff *skb,
168 						const struct iphdr *ip,
169 						unsigned char *opts)
170 {
171 	const struct tcphdr *tcp;
172 	struct tcphdr _tcph;
173 
174 	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
175 	if (!tcp)
176 		return NULL;
177 
178 	if (!tcp->syn)
179 		return NULL;
180 
181 	ctx->totlen = ntohs(ip->tot_len);
182 	ctx->df = ntohs(ip->frag_off) & IP_DF;
183 	ctx->window = ntohs(tcp->window);
184 
185 	if (tcp->doff * 4 > sizeof(struct tcphdr)) {
186 		ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
187 
188 		ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
189 				sizeof(struct tcphdr), ctx->optsize, opts);
190 	}
191 
192 	return tcp;
193 }
194 
195 bool
196 nf_osf_match(const struct sk_buff *skb, u_int8_t family,
197 	     int hooknum, struct net_device *in, struct net_device *out,
198 	     const struct nf_osf_info *info, struct net *net,
199 	     const struct list_head *nf_osf_fingers)
200 {
201 	const struct iphdr *ip = ip_hdr(skb);
202 	const struct nf_osf_user_finger *f;
203 	unsigned char opts[MAX_IPOPTLEN];
204 	const struct nf_osf_finger *kf;
205 	int fcount = 0, ttl_check;
206 	int fmatch = FMATCH_WRONG;
207 	struct nf_osf_hdr_ctx ctx;
208 	const struct tcphdr *tcp;
209 
210 	memset(&ctx, 0, sizeof(ctx));
211 
212 	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
213 	if (!tcp)
214 		return false;
215 
216 	ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
217 
218 	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
219 
220 		f = &kf->finger;
221 
222 		if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
223 			continue;
224 
225 		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
226 			continue;
227 
228 		fmatch = FMATCH_OK;
229 
230 		fcount++;
231 
232 		if (info->flags & NF_OSF_LOG)
233 			nf_log_packet(net, family, hooknum, skb,
234 				      in, out, NULL,
235 				      "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
236 				      f->genre, f->version, f->subtype,
237 				      &ip->saddr, ntohs(tcp->source),
238 				      &ip->daddr, ntohs(tcp->dest),
239 				      f->ttl - ip->ttl);
240 
241 		if ((info->flags & NF_OSF_LOG) &&
242 		    info->loglevel == NF_OSF_LOGLEVEL_FIRST)
243 			break;
244 	}
245 
246 	if (!fcount && (info->flags & NF_OSF_LOG))
247 		nf_log_packet(net, family, hooknum, skb, in, out, NULL,
248 			      "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
249 			      &ip->saddr, ntohs(tcp->source),
250 			      &ip->daddr, ntohs(tcp->dest));
251 
252 	if (fcount)
253 		fmatch = FMATCH_OK;
254 
255 	return fmatch == FMATCH_OK;
256 }
257 EXPORT_SYMBOL_GPL(nf_osf_match);
258 
259 bool nf_osf_find(const struct sk_buff *skb,
260 		 const struct list_head *nf_osf_fingers,
261 		 const int ttl_check, struct nf_osf_data *data)
262 {
263 	const struct iphdr *ip = ip_hdr(skb);
264 	const struct nf_osf_user_finger *f;
265 	unsigned char opts[MAX_IPOPTLEN];
266 	const struct nf_osf_finger *kf;
267 	struct nf_osf_hdr_ctx ctx;
268 	const struct tcphdr *tcp;
269 
270 	memset(&ctx, 0, sizeof(ctx));
271 
272 	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
273 	if (!tcp)
274 		return false;
275 
276 	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
277 		f = &kf->finger;
278 		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
279 			continue;
280 
281 		data->genre = f->genre;
282 		data->version = f->version;
283 		break;
284 	}
285 
286 	return true;
287 }
288 EXPORT_SYMBOL_GPL(nf_osf_find);
289 
290 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
291 	[OSF_ATTR_FINGER]	= { .len = sizeof(struct nf_osf_user_finger) },
292 };
293 
294 static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
295 				 struct sk_buff *skb, const struct nlmsghdr *nlh,
296 				 const struct nlattr * const osf_attrs[],
297 				 struct netlink_ext_ack *extack)
298 {
299 	struct nf_osf_user_finger *f;
300 	struct nf_osf_finger *kf = NULL, *sf;
301 	int err = 0;
302 
303 	if (!capable(CAP_NET_ADMIN))
304 		return -EPERM;
305 
306 	if (!osf_attrs[OSF_ATTR_FINGER])
307 		return -EINVAL;
308 
309 	if (!(nlh->nlmsg_flags & NLM_F_CREATE))
310 		return -EINVAL;
311 
312 	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
313 
314 	kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
315 	if (!kf)
316 		return -ENOMEM;
317 
318 	memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
319 
320 	list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
321 		if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
322 			continue;
323 
324 		kfree(kf);
325 		kf = NULL;
326 
327 		if (nlh->nlmsg_flags & NLM_F_EXCL)
328 			err = -EEXIST;
329 		break;
330 	}
331 
332 	/*
333 	 * We are protected by nfnl mutex.
334 	 */
335 	if (kf)
336 		list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
337 
338 	return err;
339 }
340 
341 static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
342 				    struct sk_buff *skb,
343 				    const struct nlmsghdr *nlh,
344 				    const struct nlattr * const osf_attrs[],
345 				    struct netlink_ext_ack *extack)
346 {
347 	struct nf_osf_user_finger *f;
348 	struct nf_osf_finger *sf;
349 	int err = -ENOENT;
350 
351 	if (!capable(CAP_NET_ADMIN))
352 		return -EPERM;
353 
354 	if (!osf_attrs[OSF_ATTR_FINGER])
355 		return -EINVAL;
356 
357 	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
358 
359 	list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
360 		if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
361 			continue;
362 
363 		/*
364 		 * We are protected by nfnl mutex.
365 		 */
366 		list_del_rcu(&sf->finger_entry);
367 		kfree_rcu(sf, rcu_head);
368 
369 		err = 0;
370 		break;
371 	}
372 
373 	return err;
374 }
375 
376 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
377 	[OSF_MSG_ADD]	= {
378 		.call		= nfnl_osf_add_callback,
379 		.attr_count	= OSF_ATTR_MAX,
380 		.policy		= nfnl_osf_policy,
381 	},
382 	[OSF_MSG_REMOVE]	= {
383 		.call		= nfnl_osf_remove_callback,
384 		.attr_count	= OSF_ATTR_MAX,
385 		.policy		= nfnl_osf_policy,
386 	},
387 };
388 
389 static const struct nfnetlink_subsystem nfnl_osf_subsys = {
390 	.name			= "osf",
391 	.subsys_id		= NFNL_SUBSYS_OSF,
392 	.cb_count		= OSF_MSG_MAX,
393 	.cb			= nfnl_osf_callbacks,
394 };
395 
396 static int __init nfnl_osf_init(void)
397 {
398 	int err = -EINVAL;
399 	int i;
400 
401 	for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
402 		INIT_LIST_HEAD(&nf_osf_fingers[i]);
403 
404 	err = nfnetlink_subsys_register(&nfnl_osf_subsys);
405 	if (err < 0) {
406 		pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
407 		goto err_out_exit;
408 	}
409 	return 0;
410 
411 err_out_exit:
412 	return err;
413 }
414 
415 static void __exit nfnl_osf_fini(void)
416 {
417 	struct nf_osf_finger *f;
418 	int i;
419 
420 	nfnetlink_subsys_unregister(&nfnl_osf_subsys);
421 
422 	rcu_read_lock();
423 	for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
424 		list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
425 			list_del_rcu(&f->finger_entry);
426 			kfree_rcu(f, rcu_head);
427 		}
428 	}
429 	rcu_read_unlock();
430 
431 	rcu_barrier();
432 }
433 
434 module_init(nfnl_osf_init);
435 module_exit(nfnl_osf_fini);
436 
437 MODULE_LICENSE("GPL");
438