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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
41unsigned dns_resolver_debug;
42module_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
70 kenter("%%%d,%s,'%s',%zu",
71 key->serial, key->description, data, datalen);
72
73 if (datalen <= 1 || !data || data[datalen - 1] != '\0')
74 return -EINVAL;
75 datalen--;
76
77 /* deal with any options embedded in the data */
Wang Lei4a2d7892010-08-11 09:37:58 +010078 end = data + datalen;
Wang Lei1a4240f2010-08-04 15:16:33 +010079 opt = memchr(data, '#', datalen);
80 if (!opt) {
Wang Lei4a2d7892010-08-11 09:37:58 +010081 /* no options: the entire data is the result */
82 kdebug("no options");
83 result_len = datalen;
84 } else {
85 const char *next_opt;
86
87 result_len = opt - data;
88 opt++;
89 kdebug("options: '%s'", opt);
90 do {
91 const char *eq;
92 int opt_len, opt_nlen, opt_vlen, tmp;
93
94 next_opt = memchr(opt, '#', end - opt) ?: end;
95 opt_len = next_opt - opt;
96 if (!opt_len) {
97 printk(KERN_WARNING
98 "Empty option to dns_resolver key %d\n",
99 key->serial);
100 return -EINVAL;
101 }
102
103 eq = memchr(opt, '=', opt_len) ?: end;
104 opt_nlen = eq - opt;
105 eq++;
106 opt_vlen = next_opt - eq; /* will be -1 if no value */
107
108 tmp = opt_vlen >= 0 ? opt_vlen : 0;
109 kdebug("option '%*.*s' val '%*.*s'",
110 opt_nlen, opt_nlen, opt, tmp, tmp, eq);
111
112 /* see if it's an error number representing a DNS error
113 * that's to be recorded as the result in this key */
114 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
115 memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
116 kdebug("dns error number option");
117 if (opt_vlen <= 0)
118 goto bad_option_value;
119
120 ret = strict_strtoul(eq, 10, &derrno);
121 if (ret < 0)
122 goto bad_option_value;
123
124 if (derrno < 1 || derrno > 511)
125 goto bad_option_value;
126
127 kdebug("dns error no. = %lu", derrno);
128 key->type_data.x[0] = -derrno;
129 continue;
130 }
131
132 bad_option_value:
133 printk(KERN_WARNING
134 "Option '%*.*s' to dns_resolver key %d:"
135 " bad/missing value\n",
136 opt_nlen, opt_nlen, opt, key->serial);
137 return -EINVAL;
138 } while (opt = next_opt + 1, opt < end);
Wang Lei1a4240f2010-08-04 15:16:33 +0100139 }
140
Wang Lei4a2d7892010-08-11 09:37:58 +0100141 /* don't cache the result if we're caching an error saying there's no
142 * result */
143 if (key->type_data.x[0]) {
144 kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
145 return 0;
146 }
147
148 kdebug("store result");
Wang Lei1a4240f2010-08-04 15:16:33 +0100149 ret = key_payload_reserve(key, result_len);
150 if (ret < 0)
151 return -EINVAL;
152
153 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
154 if (!upayload) {
155 kleave(" = -ENOMEM");
156 return -ENOMEM;
157 }
158
159 upayload->datalen = result_len;
160 memcpy(upayload->data, data, result_len);
161 upayload->data[result_len] = '\0';
162 rcu_assign_pointer(key->payload.data, upayload);
163
164 kleave(" = 0");
165 return 0;
166}
167
168/*
169 * The description is of the form "[<type>:]<domain_name>"
170 *
171 * The domain name may be a simple name or an absolute domain name (which
172 * should end with a period). The domain name is case-independent.
173 */
174static int
175dns_resolver_match(const struct key *key, const void *description)
176{
177 int slen, dlen, ret = 0;
178 const char *src = key->description, *dsp = description;
179
180 kenter("%s,%s", src, dsp);
181
182 if (!src || !dsp)
183 goto no_match;
184
185 if (strcasecmp(src, dsp) == 0)
186 goto matched;
187
188 slen = strlen(src);
189 dlen = strlen(dsp);
190 if (slen <= 0 || dlen <= 0)
191 goto no_match;
192 if (src[slen - 1] == '.')
193 slen--;
194 if (dsp[dlen - 1] == '.')
195 dlen--;
196 if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
197 goto no_match;
198
199matched:
200 ret = 1;
201no_match:
202 kleave(" = %d", ret);
203 return ret;
204}
205
Wang Lei4a2d7892010-08-11 09:37:58 +0100206/*
207 * Describe a DNS key
208 */
209static void dns_resolver_describe(const struct key *key, struct seq_file *m)
210{
211 int err = key->type_data.x[0];
212
213 seq_puts(m, key->description);
214 if (err)
215 seq_printf(m, ": %d", err);
216 else
217 seq_printf(m, ": %u", key->datalen);
218}
219
Wang Lei1a4240f2010-08-04 15:16:33 +0100220struct key_type key_type_dns_resolver = {
221 .name = "dns_resolver",
222 .instantiate = dns_resolver_instantiate,
223 .match = dns_resolver_match,
224 .revoke = user_revoke,
225 .destroy = user_destroy,
Wang Lei4a2d7892010-08-11 09:37:58 +0100226 .describe = dns_resolver_describe,
Wang Lei1a4240f2010-08-04 15:16:33 +0100227 .read = user_read,
228};
229
230static int __init init_dns_resolver(void)
231{
232 struct cred *cred;
233 struct key *keyring;
234 int ret;
235
236 printk(KERN_NOTICE "Registering the %s key type\n",
237 key_type_dns_resolver.name);
238
239 /* create an override credential set with a special thread keyring in
240 * which DNS requests are cached
241 *
242 * this is used to prevent malicious redirections from being installed
243 * with add_key().
244 */
245 cred = prepare_kernel_cred(NULL);
246 if (!cred)
247 return -ENOMEM;
248
249 keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
250 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
251 KEY_USR_VIEW | KEY_USR_READ,
252 KEY_ALLOC_NOT_IN_QUOTA);
253 if (IS_ERR(keyring)) {
254 ret = PTR_ERR(keyring);
255 goto failed_put_cred;
256 }
257
258 ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
259 if (ret < 0)
260 goto failed_put_key;
261
262 ret = register_key_type(&key_type_dns_resolver);
263 if (ret < 0)
264 goto failed_put_key;
265
266 /* instruct request_key() to use this special keyring as a cache for
267 * the results it looks up */
268 cred->thread_keyring = keyring;
269 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
270 dns_resolver_cache = cred;
271
272 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
273 return 0;
274
275failed_put_key:
276 key_put(keyring);
277failed_put_cred:
278 put_cred(cred);
279 return ret;
280}
281
282static void __exit exit_dns_resolver(void)
283{
284 key_revoke(dns_resolver_cache->thread_keyring);
285 unregister_key_type(&key_type_dns_resolver);
286 put_cred(dns_resolver_cache);
287 printk(KERN_NOTICE "Unregistered %s key type\n",
288 key_type_dns_resolver.name);
289}
290
291module_init(init_dns_resolver)
292module_exit(exit_dns_resolver)
293MODULE_LICENSE("GPL");