1/* Key type used to cache DNS lookups made by the kernel
2 *
3 * See Documentation/networking/dns_resolver.rst
4 *
5 *   Copyright (c) 2007 Igor Mammedov
6 *   Author(s): Igor Mammedov (niallain@gmail.com)
7 *              Steve French (sfrench@us.ibm.com)
8 *              Wang Lei (wang840925@gmail.com)
9 *		David Howells (dhowells@redhat.com)
10 *
11 *   This library is free software; you can redistribute it and/or modify
12 *   it under the terms of the GNU Lesser General Public License as published
13 *   by the Free Software Foundation; either version 2.1 of the License, or
14 *   (at your option) any later version.
15 *
16 *   This library is distributed in the hope that it will be useful,
17 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
18 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
19 *   the GNU Lesser General Public License for more details.
20 *
21 *   You should have received a copy of the GNU Lesser General Public License
22 *   along with this library; if not, see <http://www.gnu.org/licenses/>.
23 */
24#include <linux/module.h>
25#include <linux/moduleparam.h>
26#include <linux/slab.h>
27#include <linux/string.h>
28#include <linux/kernel.h>
29#include <linux/keyctl.h>
30#include <linux/err.h>
31#include <linux/seq_file.h>
32#include <linux/dns_resolver.h>
33#include <keys/dns_resolver-type.h>
34#include <keys/user-type.h>
35#include "internal.h"
36
37MODULE_DESCRIPTION("DNS Resolver");
38MODULE_AUTHOR("Wang Lei");
39MODULE_LICENSE("GPL");
40
41unsigned int dns_resolver_debug;
42module_param_named(debug, dns_resolver_debug, uint, 0644);
43MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
44
45const struct cred *dns_resolver_cache;
46
47#define	DNS_ERRORNO_OPTION	"dnserror"
48
49/*
50 * Preparse instantiation data for a dns_resolver key.
51 *
52 * For normal hostname lookups, the data must be a NUL-terminated string, with
53 * the NUL char accounted in datalen.
54 *
55 * If the data contains a '#' characters, then we take the clause after each
56 * one to be an option of the form 'key=value'.  The actual data of interest is
57 * the string leading up to the first '#'.  For instance:
58 *
59 *        "ip1,ip2,...#foo=bar"
60 *
61 * For server list requests, the data must begin with a NUL char and be
62 * followed by a byte indicating the version of the data format.  Version 1
63 * looks something like (note this is packed):
64 *
65 *	u8      Non-string marker (ie. 0)
66 *	u8	Content (DNS_PAYLOAD_IS_*)
67 *	u8	Version (e.g. 1)
68 *	u8	Source of server list
69 *	u8	Lookup status of server list
70 *	u8	Number of servers
71 *	foreach-server {
72 *		__le16	Name length
73 *		__le16	Priority (as per SRV record, low first)
74 *		__le16	Weight (as per SRV record, higher first)
75 *		__le16	Port
76 *		u8	Source of address list
77 *		u8	Lookup status of address list
78 *		u8	Protocol (DNS_SERVER_PROTOCOL_*)
79 *		u8	Number of addresses
80 *		char[]	Name (not NUL-terminated)
81 *		foreach-address {
82 *			u8		Family (DNS_ADDRESS_IS_*)
83 *			union {
84 *				u8[4]	ipv4_addr
85 *				u8[16]	ipv6_addr
86 *			}
87 *		}
88 *	}
89 *
90 */
91static int
92dns_resolver_preparse(struct key_preparsed_payload *prep)
93{
94	struct user_key_payload *upayload;
95	unsigned long derrno;
96	int ret;
97	int datalen = prep->datalen, result_len = 0;
98	const char *data = prep->data, *end, *opt;
99
100	if (datalen <= 1 || !data)
101		return -EINVAL;
102
103	if (data[0] == 0) {
104		const struct dns_server_list_v1_header *v1;
105
106		/* It may be a server list. */
107		if (datalen < sizeof(*v1))
108			return -EINVAL;
109
110		v1 = (const struct dns_server_list_v1_header *)data;
111		kenter("[%u,%u],%u", v1->hdr.content, v1->hdr.version, datalen);
112		if (v1->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST) {
113			pr_warn_ratelimited(
114				"dns_resolver: Unsupported content type (%u)\n",
115				v1->hdr.content);
116			return -EINVAL;
117		}
118
119		if (v1->hdr.version != 1) {
120			pr_warn_ratelimited(
121				"dns_resolver: Unsupported server list version (%u)\n",
122				v1->hdr.version);
123			return -EINVAL;
124		}
125
126		if ((v1->status != DNS_LOOKUP_GOOD &&
127		     v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
128			if (prep->expiry == TIME64_MAX)
129				prep->expiry = ktime_get_real_seconds() + 1;
130		}
131
132		result_len = datalen;
133		goto store_result;
134	}
135
136	kenter("'%*.*s',%u", datalen, datalen, data, datalen);
137
138	if (!data || data[datalen - 1] != '\0')
139		return -EINVAL;
140	datalen--;
141
142	/* deal with any options embedded in the data */
143	end = data + datalen;
144	opt = memchr(data, '#', datalen);
145	if (!opt) {
146		/* no options: the entire data is the result */
147		kdebug("no options");
148		result_len = datalen;
149	} else {
150		const char *next_opt;
151
152		result_len = opt - data;
153		opt++;
154		kdebug("options: '%s'", opt);
155		do {
156			int opt_len, opt_nlen;
157			const char *eq;
158			char optval[128];
159
160			next_opt = memchr(opt, '#', end - opt) ?: end;
161			opt_len = next_opt - opt;
162			if (opt_len <= 0 || opt_len > sizeof(optval)) {
163				pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
164						    opt_len);
165				return -EINVAL;
166			}
167
168			eq = memchr(opt, '=', opt_len);
169			if (eq) {
170				opt_nlen = eq - opt;
171				eq++;
172				memcpy(optval, eq, next_opt - eq);
173				optval[next_opt - eq] = '\0';
174			} else {
175				opt_nlen = opt_len;
176				optval[0] = '\0';
177			}
178
179			kdebug("option '%*.*s' val '%s'",
180			       opt_nlen, opt_nlen, opt, optval);
181
182			/* see if it's an error number representing a DNS error
183			 * that's to be recorded as the result in this key */
184			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
185			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
186				kdebug("dns error number option");
187
188				ret = kstrtoul(optval, 10, &derrno);
189				if (ret < 0)
190					goto bad_option_value;
191
192				if (derrno < 1 || derrno > 511)
193					goto bad_option_value;
194
195				kdebug("dns error no. = %lu", derrno);
196				prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
197				continue;
198			}
199
200		bad_option_value:
201			pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
202					    opt_nlen, opt_nlen, opt);
203			return -EINVAL;
204		} while (opt = next_opt + 1, opt < end);
205	}
206
207	/* don't cache the result if we're caching an error saying there's no
208	 * result */
209	if (prep->payload.data[dns_key_error]) {
210		kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
211		return 0;
212	}
213
214store_result:
215	kdebug("store result");
216	prep->quotalen = result_len;
217
218	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
219	if (!upayload) {
220		kleave(" = -ENOMEM");
221		return -ENOMEM;
222	}
223
224	upayload->datalen = result_len;
225	memcpy(upayload->data, data, result_len);
226	upayload->data[result_len] = '\0';
227
228	prep->payload.data[dns_key_data] = upayload;
229	kleave(" = 0");
230	return 0;
231}
232
233/*
234 * Clean up the preparse data
235 */
236static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
237{
238	pr_devel("==>%s()\n", __func__);
239
240	kfree(prep->payload.data[dns_key_data]);
241}
242
243/*
244 * The description is of the form "[<type>:]<domain_name>"
245 *
246 * The domain name may be a simple name or an absolute domain name (which
247 * should end with a period).  The domain name is case-independent.
248 */
249static bool dns_resolver_cmp(const struct key *key,
250			     const struct key_match_data *match_data)
251{
252	int slen, dlen, ret = 0;
253	const char *src = key->description, *dsp = match_data->raw_data;
254
255	kenter("%s,%s", src, dsp);
256
257	if (!src || !dsp)
258		goto no_match;
259
260	if (strcasecmp(src, dsp) == 0)
261		goto matched;
262
263	slen = strlen(src);
264	dlen = strlen(dsp);
265	if (slen <= 0 || dlen <= 0)
266		goto no_match;
267	if (src[slen - 1] == '.')
268		slen--;
269	if (dsp[dlen - 1] == '.')
270		dlen--;
271	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
272		goto no_match;
273
274matched:
275	ret = 1;
276no_match:
277	kleave(" = %d", ret);
278	return ret;
279}
280
281/*
282 * Preparse the match criterion.
283 */
284static int dns_resolver_match_preparse(struct key_match_data *match_data)
285{
286	match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
287	match_data->cmp = dns_resolver_cmp;
288	return 0;
289}
290
291/*
292 * Describe a DNS key
293 */
294static void dns_resolver_describe(const struct key *key, struct seq_file *m)
295{
296	seq_puts(m, key->description);
297	if (key_is_positive(key)) {
298		int err = PTR_ERR(key->payload.data[dns_key_error]);
299
300		if (err)
301			seq_printf(m, ": %d", err);
302		else
303			seq_printf(m, ": %u", key->datalen);
304	}
305}
306
307/*
308 * read the DNS data
309 * - the key's semaphore is read-locked
310 */
311static long dns_resolver_read(const struct key *key,
312			      char *buffer, size_t buflen)
313{
314	int err = PTR_ERR(key->payload.data[dns_key_error]);
315
316	if (err)
317		return err;
318
319	return user_read(key, buffer, buflen);
320}
321
322struct key_type key_type_dns_resolver = {
323	.name		= "dns_resolver",
324	.flags		= KEY_TYPE_NET_DOMAIN | KEY_TYPE_INSTANT_REAP,
325	.preparse	= dns_resolver_preparse,
326	.free_preparse	= dns_resolver_free_preparse,
327	.instantiate	= generic_key_instantiate,
328	.match_preparse	= dns_resolver_match_preparse,
329	.revoke		= user_revoke,
330	.destroy	= user_destroy,
331	.describe	= dns_resolver_describe,
332	.read		= dns_resolver_read,
333};
334
335static int __init init_dns_resolver(void)
336{
337	struct cred *cred;
338	struct key *keyring;
339	int ret;
340
341	/* create an override credential set with a special thread keyring in
342	 * which DNS requests are cached
343	 *
344	 * this is used to prevent malicious redirections from being installed
345	 * with add_key().
346	 */
347	cred = prepare_kernel_cred(&init_task);
348	if (!cred)
349		return -ENOMEM;
350
351	keyring = keyring_alloc(".dns_resolver",
352				GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
353				(KEY_POS_ALL & ~KEY_POS_SETATTR) |
354				KEY_USR_VIEW | KEY_USR_READ,
355				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
356	if (IS_ERR(keyring)) {
357		ret = PTR_ERR(keyring);
358		goto failed_put_cred;
359	}
360
361	ret = register_key_type(&key_type_dns_resolver);
362	if (ret < 0)
363		goto failed_put_key;
364
365	/* instruct request_key() to use this special keyring as a cache for
366	 * the results it looks up */
367	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
368	cred->thread_keyring = keyring;
369	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
370	dns_resolver_cache = cred;
371
372	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
373	return 0;
374
375failed_put_key:
376	key_put(keyring);
377failed_put_cred:
378	put_cred(cred);
379	return ret;
380}
381
382static void __exit exit_dns_resolver(void)
383{
384	key_revoke(dns_resolver_cache->thread_keyring);
385	unregister_key_type(&key_type_dns_resolver);
386	put_cred(dns_resolver_cache);
387}
388
389module_init(init_dns_resolver)
390module_exit(exit_dns_resolver)
391MODULE_LICENSE("GPL");
392