summaryrefslogtreecommitdiffstats
path: root/net/dns_resolver/dns_key.c
blob: 14b2c3d6e526033c07052c2dcde140c676693b35 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
/* Key type used to cache DNS lookups made by the kernel
 *
 * See Documentation/networking/dns_resolver.txt
 *
 *   Copyright (c) 2007 Igor Mammedov
 *   Author(s): Igor Mammedov (niallain@gmail.com)
 *              Steve French (sfrench@us.ibm.com)
 *              Wang Lei (wang840925@gmail.com)
 *		David Howells (dhowells@redhat.com)
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as published
 *   by the Free Software Foundation; either version 2.1 of the License, or
 *   (at your option) any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 *   the GNU Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public License
 *   along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/keyctl.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>
#include "internal.h"

MODULE_DESCRIPTION("DNS Resolver");
MODULE_AUTHOR("Wang Lei");
MODULE_LICENSE("GPL");

unsigned dns_resolver_debug;
module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");

const struct cred *dns_resolver_cache;

#define	DNS_ERRORNO_OPTION	"dnserror"

/*
 * Instantiate a user defined key for dns_resolver.
 *
 * The data must be a NUL-terminated string, with the NUL char accounted in
 * datalen.
 *
 * If the data contains a '#' characters, then we take the clause after each
 * one to be an option of the form 'key=value'.  The actual data of interest is
 * the string leading up to the first '#'.  For instance:
 *
 *        "ip1,ip2,...#foo=bar"
 */
static int
dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
{
	struct user_key_payload *upayload;
	unsigned long derrno;
	int ret;
	size_t result_len = 0;
	const char *data = _data, *end, *opt;

	kenter("%%%d,%s,'%*.*s',%zu",
	       key->serial, key->description,
	       (int)datalen, (int)datalen, data, datalen);

	if (datalen <= 1 || !data || data[datalen - 1] != '\0')
		return -EINVAL;
	datalen--;

	/* deal with any options embedded in the data */
	end = data + datalen;
	opt = memchr(data, '#', datalen);
	if (!opt) {
		/* no options: the entire data is the result */
		kdebug("no options");
		result_len = datalen;
	} else {
		const char *next_opt;

		result_len = opt - data;
		opt++;
		kdebug("options: '%s'", opt);
		do {
			const char *eq;
			int opt_len, opt_nlen, opt_vlen, tmp;

			next_opt = memchr(opt, '#', end - opt) ?: end;
			opt_len = next_opt - opt;
			if (!opt_len) {
				printk(KERN_WARNING
				       "Empty option to dns_resolver key %d\n",
				       key->serial);
				return -EINVAL;
			}

			eq = memchr(opt, '=', opt_len) ?: end;
			opt_nlen = eq - opt;
			eq++;
			opt_vlen = next_opt - eq; /* will be -1 if no value */

			tmp = opt_vlen >= 0 ? opt_vlen : 0;
			kdebug("option '%*.*s' val '%*.*s'",
			       opt_nlen, opt_nlen, opt, tmp, tmp, eq);

			/* see if it's an error number representing a DNS error
			 * that's to be recorded as the result in this key */
			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
				kdebug("dns error number option");
				if (opt_vlen <= 0)
					goto bad_option_value;

				ret = strict_strtoul(eq, 10, &derrno);
				if (ret < 0)
					goto bad_option_value;

				if (derrno < 1 || derrno > 511)
					goto bad_option_value;

				kdebug("dns error no. = %lu", derrno);
				key->type_data.x[0] = -derrno;
				continue;
			}

		bad_option_value:
			printk(KERN_WARNING
			       "Option '%*.*s' to dns_resolver key %d:"
			       " bad/missing value\n",
			       opt_nlen, opt_nlen, opt, key->serial);
			return -EINVAL;
		} while (opt = next_opt + 1, opt < end);
	}

	/* don't cache the result if we're caching an error saying there's no
	 * result */
	if (key->type_data.x[0]) {
		kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
		return 0;
	}

	kdebug("store result");
	ret = key_payload_reserve(key, result_len);
	if (ret < 0)
		return -EINVAL;

	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
	if (!upayload) {
		kleave(" = -ENOMEM");
		return -ENOMEM;
	}

	upayload->datalen = result_len;
	memcpy(upayload->data, data, result_len);
	upayload->data[result_len] = '\0';
	rcu_assign_pointer(key->payload.data, upayload);

	kleave(" = 0");
	return 0;
}

/*
 * The description is of the form "[<type>:]<domain_name>"
 *
 * The domain name may be a simple name or an absolute domain name (which
 * should end with a period).  The domain name is case-independent.
 */
static int
dns_resolver_match(const struct key *key, const void *description)
{
	int slen, dlen, ret = 0;
	const char *src = key->description, *dsp = description;

	kenter("%s,%s", src, dsp);

	if (!src || !dsp)
		goto no_match;

	if (strcasecmp(src, dsp) == 0)
		goto matched;

	slen = strlen(src);
	dlen = strlen(dsp);
	if (slen <= 0 || dlen <= 0)
		goto no_match;
	if (src[slen - 1] == '.')
		slen--;
	if (dsp[dlen - 1] == '.')
		dlen--;
	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
		goto no_match;

matched:
	ret = 1;
no_match:
	kleave(" = %d", ret);
	return ret;
}

/*
 * Describe a DNS key
 */
static void dns_resolver_describe(const struct key *key, struct seq_file *m)
{
	int err = key->type_data.x[0];

	seq_puts(m, key->description);
	if (key_is_instantiated(key)) {
		if (err)
			seq_printf(m, ": %d", err);
		else
			seq_printf(m, ": %u", key->datalen);
	}
}

/*
 * read the DNS data
 * - the key's semaphore is read-locked
 */
static long dns_resolver_read(const struct key *key,
			      char __user *buffer, size_t buflen)
{
	if (key->type_data.x[0])
		return key->type_data.x[0];

	return user_read(key, buffer, buflen);
}

struct key_type key_type_dns_resolver = {
	.name		= "dns_resolver",
	.instantiate	= dns_resolver_instantiate,
	.match		= dns_resolver_match,
	.revoke		= user_revoke,
	.destroy	= user_destroy,
	.describe	= dns_resolver_describe,
	.read		= dns_resolver_read,
};

static int __init init_dns_resolver(void)
{
	struct cred *cred;
	struct key *keyring;
	int ret;

	/* create an override credential set with a special thread keyring in
	 * which DNS requests are cached
	 *
	 * this is used to prevent malicious redirections from being installed
	 * with add_key().
	 */
	cred = prepare_kernel_cred(NULL);
	if (!cred)
		return -ENOMEM;

	keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
			    (KEY_POS_ALL & ~KEY_POS_SETATTR) |
			    KEY_USR_VIEW | KEY_USR_READ,
			    KEY_ALLOC_NOT_IN_QUOTA);
	if (IS_ERR(keyring)) {
		ret = PTR_ERR(keyring);
		goto failed_put_cred;
	}

	ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
	if (ret < 0)
		goto failed_put_key;

	ret = register_key_type(&key_type_dns_resolver);
	if (ret < 0)
		goto failed_put_key;

	/* instruct request_key() to use this special keyring as a cache for
	 * the results it looks up */
	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
	cred->thread_keyring = keyring;
	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
	dns_resolver_cache = cred;

	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
	return 0;

failed_put_key:
	key_put(keyring);
failed_put_cred:
	put_cred(cred);
	return ret;
}

static void __exit exit_dns_resolver(void)
{
	key_revoke(dns_resolver_cache->thread_keyring);
	unregister_key_type(&key_type_dns_resolver);
	put_cred(dns_resolver_cache);
}

module_init(init_dns_resolver)
module_exit(exit_dns_resolver)
MODULE_LICENSE("GPL");