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Wang Lei1a4240f2010-08-04 15:16:33 +01001/* 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, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25#include <linux/module.h>
26#include <linux/moduleparam.h>
27#include <linux/slab.h>
28#include <linux/string.h>
29#include <linux/kernel.h>
30#include <linux/keyctl.h>
Stephen Rothwellaf352fe2010-08-06 03:13:47 +010031#include <linux/err.h>
Wang Lei4a2d7892010-08-11 09:37:58 +010032#include <linux/seq_file.h>
Wang Lei1a4240f2010-08-04 15:16:33 +010033#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
Eric Dumazet95c96172012-04-15 05:58:06 +000041unsigned int dns_resolver_debug;
Wang Lei1a4240f2010-08-04 15:16:33 +010042module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
43MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
44
45const struct cred *dns_resolver_cache;
46
Wang Lei4a2d7892010-08-11 09:37:58 +010047#define DNS_ERRORNO_OPTION "dnserror"
48
Wang Lei1a4240f2010-08-04 15:16:33 +010049/*
50 * Instantiate a user defined key for dns_resolver.
51 *
52 * The data must be a NUL-terminated string, with the NUL char accounted in
53 * 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 */
61static int
62dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
63{
64 struct user_key_payload *upayload;
Wang Lei4a2d7892010-08-11 09:37:58 +010065 unsigned long derrno;
Wang Lei1a4240f2010-08-04 15:16:33 +010066 int ret;
67 size_t result_len = 0;
Wang Lei4a2d7892010-08-11 09:37:58 +010068 const char *data = _data, *end, *opt;
Wang Lei1a4240f2010-08-04 15:16:33 +010069
David Howells1362fa02011-03-03 11:28:58 +000070 kenter("%%%d,%s,'%*.*s',%zu",
71 key->serial, key->description,
72 (int)datalen, (int)datalen, data, datalen);
Wang Lei1a4240f2010-08-04 15:16:33 +010073
74 if (datalen <= 1 || !data || data[datalen - 1] != '\0')
75 return -EINVAL;
76 datalen--;
77
78 /* deal with any options embedded in the data */
Wang Lei4a2d7892010-08-11 09:37:58 +010079 end = data + datalen;
Wang Lei1a4240f2010-08-04 15:16:33 +010080 opt = memchr(data, '#', datalen);
81 if (!opt) {
Wang Lei4a2d7892010-08-11 09:37:58 +010082 /* no options: the entire data is the result */
83 kdebug("no options");
84 result_len = datalen;
85 } else {
86 const char *next_opt;
87
88 result_len = opt - data;
89 opt++;
90 kdebug("options: '%s'", opt);
91 do {
92 const char *eq;
93 int opt_len, opt_nlen, opt_vlen, tmp;
94
95 next_opt = memchr(opt, '#', end - opt) ?: end;
96 opt_len = next_opt - opt;
97 if (!opt_len) {
98 printk(KERN_WARNING
99 "Empty option to dns_resolver key %d\n",
100 key->serial);
101 return -EINVAL;
102 }
103
104 eq = memchr(opt, '=', opt_len) ?: end;
105 opt_nlen = eq - opt;
106 eq++;
107 opt_vlen = next_opt - eq; /* will be -1 if no value */
108
109 tmp = opt_vlen >= 0 ? opt_vlen : 0;
110 kdebug("option '%*.*s' val '%*.*s'",
111 opt_nlen, opt_nlen, opt, tmp, tmp, eq);
112
113 /* see if it's an error number representing a DNS error
114 * that's to be recorded as the result in this key */
115 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
116 memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
117 kdebug("dns error number option");
118 if (opt_vlen <= 0)
119 goto bad_option_value;
120
121 ret = strict_strtoul(eq, 10, &derrno);
122 if (ret < 0)
123 goto bad_option_value;
124
125 if (derrno < 1 || derrno > 511)
126 goto bad_option_value;
127
128 kdebug("dns error no. = %lu", derrno);
129 key->type_data.x[0] = -derrno;
130 continue;
131 }
132
133 bad_option_value:
134 printk(KERN_WARNING
135 "Option '%*.*s' to dns_resolver key %d:"
136 " bad/missing value\n",
137 opt_nlen, opt_nlen, opt, key->serial);
138 return -EINVAL;
139 } while (opt = next_opt + 1, opt < end);
Wang Lei1a4240f2010-08-04 15:16:33 +0100140 }
141
Wang Lei4a2d7892010-08-11 09:37:58 +0100142 /* don't cache the result if we're caching an error saying there's no
143 * result */
144 if (key->type_data.x[0]) {
145 kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
146 return 0;
147 }
148
149 kdebug("store result");
Wang Lei1a4240f2010-08-04 15:16:33 +0100150 ret = key_payload_reserve(key, result_len);
151 if (ret < 0)
152 return -EINVAL;
153
154 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
155 if (!upayload) {
156 kleave(" = -ENOMEM");
157 return -ENOMEM;
158 }
159
160 upayload->datalen = result_len;
161 memcpy(upayload->data, data, result_len);
162 upayload->data[result_len] = '\0';
163 rcu_assign_pointer(key->payload.data, upayload);
164
165 kleave(" = 0");
166 return 0;
167}
168
169/*
170 * The description is of the form "[<type>:]<domain_name>"
171 *
172 * The domain name may be a simple name or an absolute domain name (which
173 * should end with a period). The domain name is case-independent.
174 */
175static int
176dns_resolver_match(const struct key *key, const void *description)
177{
178 int slen, dlen, ret = 0;
179 const char *src = key->description, *dsp = description;
180
181 kenter("%s,%s", src, dsp);
182
183 if (!src || !dsp)
184 goto no_match;
185
186 if (strcasecmp(src, dsp) == 0)
187 goto matched;
188
189 slen = strlen(src);
190 dlen = strlen(dsp);
191 if (slen <= 0 || dlen <= 0)
192 goto no_match;
193 if (src[slen - 1] == '.')
194 slen--;
195 if (dsp[dlen - 1] == '.')
196 dlen--;
197 if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
198 goto no_match;
199
200matched:
201 ret = 1;
202no_match:
203 kleave(" = %d", ret);
204 return ret;
205}
206
Wang Lei4a2d7892010-08-11 09:37:58 +0100207/*
208 * Describe a DNS key
209 */
210static void dns_resolver_describe(const struct key *key, struct seq_file *m)
211{
212 int err = key->type_data.x[0];
213
214 seq_puts(m, key->description);
David Howells78b72802011-03-11 17:57:23 +0000215 if (key_is_instantiated(key)) {
216 if (err)
217 seq_printf(m, ": %d", err);
218 else
219 seq_printf(m, ": %u", key->datalen);
220 }
Wang Lei4a2d7892010-08-11 09:37:58 +0100221}
222
David Howells1362fa02011-03-03 11:28:58 +0000223/*
224 * read the DNS data
225 * - the key's semaphore is read-locked
226 */
227static long dns_resolver_read(const struct key *key,
228 char __user *buffer, size_t buflen)
229{
230 if (key->type_data.x[0])
231 return key->type_data.x[0];
232
233 return user_read(key, buffer, buflen);
234}
235
Wang Lei1a4240f2010-08-04 15:16:33 +0100236struct key_type key_type_dns_resolver = {
237 .name = "dns_resolver",
238 .instantiate = dns_resolver_instantiate,
239 .match = dns_resolver_match,
240 .revoke = user_revoke,
241 .destroy = user_destroy,
Wang Lei4a2d7892010-08-11 09:37:58 +0100242 .describe = dns_resolver_describe,
David Howells1362fa02011-03-03 11:28:58 +0000243 .read = dns_resolver_read,
Wang Lei1a4240f2010-08-04 15:16:33 +0100244};
245
246static int __init init_dns_resolver(void)
247{
248 struct cred *cred;
249 struct key *keyring;
250 int ret;
251
Wang Lei1a4240f2010-08-04 15:16:33 +0100252 /* create an override credential set with a special thread keyring in
253 * which DNS requests are cached
254 *
255 * this is used to prevent malicious redirections from being installed
256 * with add_key().
257 */
258 cred = prepare_kernel_cred(NULL);
259 if (!cred)
260 return -ENOMEM;
261
262 keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
263 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
264 KEY_USR_VIEW | KEY_USR_READ,
265 KEY_ALLOC_NOT_IN_QUOTA);
266 if (IS_ERR(keyring)) {
267 ret = PTR_ERR(keyring);
268 goto failed_put_cred;
269 }
270
271 ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
272 if (ret < 0)
273 goto failed_put_key;
274
275 ret = register_key_type(&key_type_dns_resolver);
276 if (ret < 0)
277 goto failed_put_key;
278
279 /* instruct request_key() to use this special keyring as a cache for
280 * the results it looks up */
David Howells700920e2012-01-18 15:31:45 +0000281 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
Wang Lei1a4240f2010-08-04 15:16:33 +0100282 cred->thread_keyring = keyring;
283 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
284 dns_resolver_cache = cred;
285
286 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
287 return 0;
288
289failed_put_key:
290 key_put(keyring);
291failed_put_cred:
292 put_cred(cred);
293 return ret;
294}
295
296static void __exit exit_dns_resolver(void)
297{
298 key_revoke(dns_resolver_cache->thread_keyring);
299 unregister_key_type(&key_type_dns_resolver);
300 put_cred(dns_resolver_cache);
Wang Lei1a4240f2010-08-04 15:16:33 +0100301}
302
303module_init(init_dns_resolver)
304module_exit(exit_dns_resolver)
305MODULE_LICENSE("GPL");