1/* Key type used to cache DNS lookups made by the kernel
2 *
3 * See Documentation/networking/dns_resolver.txt
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 <keys/dns_resolver-type.h>
33#include <keys/user-type.h>
34#include "internal.h"
35
36MODULE_DESCRIPTION("DNS Resolver");
37MODULE_AUTHOR("Wang Lei");
38MODULE_LICENSE("GPL");
39
40unsigned int dns_resolver_debug;
41module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
42MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
43
44const struct cred *dns_resolver_cache;
45
46#define	DNS_ERRORNO_OPTION	"dnserror"
47
48/*
49 * Preparse instantiation data for a dns_resolver key.
50 *
51 * The data must be a NUL-terminated string, with the NUL char accounted in
52 * datalen.
53 *
54 * If the data contains a '#' characters, then we take the clause after each
55 * one to be an option of the form 'key=value'.  The actual data of interest is
56 * the string leading up to the first '#'.  For instance:
57 *
58 *        "ip1,ip2,...#foo=bar"
59 */
60static int
61dns_resolver_preparse(struct key_preparsed_payload *prep)
62{
63	struct user_key_payload *upayload;
64	unsigned long derrno;
65	int ret;
66	int datalen = prep->datalen, result_len = 0;
67	const char *data = prep->data, *end, *opt;
68
69	kenter("'%*.*s',%u", datalen, datalen, data, datalen);
70
71	if (datalen <= 1 || !data || data[datalen - 1] != '\0')
72		return -EINVAL;
73	datalen--;
74
75	/* deal with any options embedded in the data */
76	end = data + datalen;
77	opt = memchr(data, '#', datalen);
78	if (!opt) {
79		/* no options: the entire data is the result */
80		kdebug("no options");
81		result_len = datalen;
82	} else {
83		const char *next_opt;
84
85		result_len = opt - data;
86		opt++;
87		kdebug("options: '%s'", opt);
88		do {
89			const char *eq;
90			int opt_len, opt_nlen, opt_vlen, tmp;
91
92			next_opt = memchr(opt, '#', end - opt) ?: end;
93			opt_len = next_opt - opt;
94			if (!opt_len) {
95				printk(KERN_WARNING
96				       "Empty option to dns_resolver key\n");
97				return -EINVAL;
98			}
99
100			eq = memchr(opt, '=', opt_len) ?: end;
101			opt_nlen = eq - opt;
102			eq++;
103			opt_vlen = next_opt - eq; /* will be -1 if no value */
104
105			tmp = opt_vlen >= 0 ? opt_vlen : 0;
106			kdebug("option '%*.*s' val '%*.*s'",
107			       opt_nlen, opt_nlen, opt, tmp, tmp, eq);
108
109			/* see if it's an error number representing a DNS error
110			 * that's to be recorded as the result in this key */
111			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
112			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
113				kdebug("dns error number option");
114				if (opt_vlen <= 0)
115					goto bad_option_value;
116
117				ret = kstrtoul(eq, 10, &derrno);
118				if (ret < 0)
119					goto bad_option_value;
120
121				if (derrno < 1 || derrno > 511)
122					goto bad_option_value;
123
124				kdebug("dns error no. = %lu", derrno);
125				prep->type_data[0] = ERR_PTR(-derrno);
126				continue;
127			}
128
129		bad_option_value:
130			printk(KERN_WARNING
131			       "Option '%*.*s' to dns_resolver key:"
132			       " bad/missing value\n",
133			       opt_nlen, opt_nlen, opt);
134			return -EINVAL;
135		} while (opt = next_opt + 1, opt < end);
136	}
137
138	/* don't cache the result if we're caching an error saying there's no
139	 * result */
140	if (prep->type_data[0]) {
141		kleave(" = 0 [h_error %ld]", PTR_ERR(prep->type_data[0]));
142		return 0;
143	}
144
145	kdebug("store result");
146	prep->quotalen = result_len;
147
148	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
149	if (!upayload) {
150		kleave(" = -ENOMEM");
151		return -ENOMEM;
152	}
153
154	upayload->datalen = result_len;
155	memcpy(upayload->data, data, result_len);
156	upayload->data[result_len] = '\0';
157
158	prep->payload[0] = upayload;
159	kleave(" = 0");
160	return 0;
161}
162
163/*
164 * Clean up the preparse data
165 */
166static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
167{
168	pr_devel("==>%s()\n", __func__);
169
170	kfree(prep->payload[0]);
171}
172
173/*
174 * The description is of the form "[<type>:]<domain_name>"
175 *
176 * The domain name may be a simple name or an absolute domain name (which
177 * should end with a period).  The domain name is case-independent.
178 */
179static bool dns_resolver_cmp(const struct key *key,
180			     const struct key_match_data *match_data)
181{
182	int slen, dlen, ret = 0;
183	const char *src = key->description, *dsp = match_data->raw_data;
184
185	kenter("%s,%s", src, dsp);
186
187	if (!src || !dsp)
188		goto no_match;
189
190	if (strcasecmp(src, dsp) == 0)
191		goto matched;
192
193	slen = strlen(src);
194	dlen = strlen(dsp);
195	if (slen <= 0 || dlen <= 0)
196		goto no_match;
197	if (src[slen - 1] == '.')
198		slen--;
199	if (dsp[dlen - 1] == '.')
200		dlen--;
201	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
202		goto no_match;
203
204matched:
205	ret = 1;
206no_match:
207	kleave(" = %d", ret);
208	return ret;
209}
210
211/*
212 * Preparse the match criterion.
213 */
214static int dns_resolver_match_preparse(struct key_match_data *match_data)
215{
216	match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
217	match_data->cmp = dns_resolver_cmp;
218	return 0;
219}
220
221/*
222 * Describe a DNS key
223 */
224static void dns_resolver_describe(const struct key *key, struct seq_file *m)
225{
226	int err = key->type_data.x[0];
227
228	seq_puts(m, key->description);
229	if (key_is_instantiated(key)) {
230		if (err)
231			seq_printf(m, ": %d", err);
232		else
233			seq_printf(m, ": %u", key->datalen);
234	}
235}
236
237/*
238 * read the DNS data
239 * - the key's semaphore is read-locked
240 */
241static long dns_resolver_read(const struct key *key,
242			      char __user *buffer, size_t buflen)
243{
244	if (key->type_data.x[0])
245		return key->type_data.x[0];
246
247	return user_read(key, buffer, buflen);
248}
249
250struct key_type key_type_dns_resolver = {
251	.name		= "dns_resolver",
252	.preparse	= dns_resolver_preparse,
253	.free_preparse	= dns_resolver_free_preparse,
254	.instantiate	= generic_key_instantiate,
255	.match_preparse	= dns_resolver_match_preparse,
256	.revoke		= user_revoke,
257	.destroy	= user_destroy,
258	.describe	= dns_resolver_describe,
259	.read		= dns_resolver_read,
260};
261
262static int __init init_dns_resolver(void)
263{
264	struct cred *cred;
265	struct key *keyring;
266	int ret;
267
268	/* create an override credential set with a special thread keyring in
269	 * which DNS requests are cached
270	 *
271	 * this is used to prevent malicious redirections from being installed
272	 * with add_key().
273	 */
274	cred = prepare_kernel_cred(NULL);
275	if (!cred)
276		return -ENOMEM;
277
278	keyring = keyring_alloc(".dns_resolver",
279				GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
280				(KEY_POS_ALL & ~KEY_POS_SETATTR) |
281				KEY_USR_VIEW | KEY_USR_READ,
282				KEY_ALLOC_NOT_IN_QUOTA, NULL);
283	if (IS_ERR(keyring)) {
284		ret = PTR_ERR(keyring);
285		goto failed_put_cred;
286	}
287
288	ret = register_key_type(&key_type_dns_resolver);
289	if (ret < 0)
290		goto failed_put_key;
291
292	/* instruct request_key() to use this special keyring as a cache for
293	 * the results it looks up */
294	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
295	cred->thread_keyring = keyring;
296	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
297	dns_resolver_cache = cred;
298
299	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
300	return 0;
301
302failed_put_key:
303	key_put(keyring);
304failed_put_cred:
305	put_cred(cred);
306	return ret;
307}
308
309static void __exit exit_dns_resolver(void)
310{
311	key_revoke(dns_resolver_cache->thread_keyring);
312	unregister_key_type(&key_type_dns_resolver);
313	put_cred(dns_resolver_cache);
314}
315
316module_init(init_dns_resolver)
317module_exit(exit_dns_resolver)
318MODULE_LICENSE("GPL");
319
320