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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, 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>
31#include <linux/err.h>
32#include <linux/seq_file.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, S_IWUSR | S_IRUGO);
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 * 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;
65 unsigned long derrno;
66 int ret;
67 size_t result_len = 0;
68 const char *data = _data, *end, *opt;
69
70 kenter("%%%d,%s,'%*.*s',%zu",
71 key->serial, key->description,
72 (int)datalen, (int)datalen, data, datalen);
73
74 if (datalen <= 1 || !data || data[datalen - 1] != '\0')
75 return -EINVAL;
76 datalen--;
77
78 /* deal with any options embedded in the data */
79 end = data + datalen;
80 opt = memchr(data, '#', datalen);
81 if (!opt) {
82 /* 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);
140 }
141
142 /* 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");
150 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
207/*
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);
215 if (key_is_instantiated(key)) {
216 if (err)
217 seq_printf(m, ": %d", err);
218 else
219 seq_printf(m, ": %u", key->datalen);
220 }
221}
222
223/*
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
236struct 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,
242 .describe = dns_resolver_describe,
243 .read = dns_resolver_read,
244};
245
246static int __init init_dns_resolver(void)
247{
248 struct cred *cred;
249 struct key *keyring;
250 int ret;
251
252 /* 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 */
281 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
282 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);
301}
302
303module_init(init_dns_resolver)
304module_exit(exit_dns_resolver)
305MODULE_LICENSE("GPL");
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->payload.data[dns_key_error] = 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->payload.data[dns_key_error]) {
141 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
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.data[dns_key_data] = 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.data[dns_key_data]);
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 seq_puts(m, key->description);
227 if (key_is_instantiated(key)) {
228 int err = PTR_ERR(key->payload.data[dns_key_error]);
229
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 int err = PTR_ERR(key->payload.data[dns_key_error]);
245
246 if (err)
247 return err;
248
249 return user_read(key, buffer, buflen);
250}
251
252struct key_type key_type_dns_resolver = {
253 .name = "dns_resolver",
254 .preparse = dns_resolver_preparse,
255 .free_preparse = dns_resolver_free_preparse,
256 .instantiate = generic_key_instantiate,
257 .match_preparse = dns_resolver_match_preparse,
258 .revoke = user_revoke,
259 .destroy = user_destroy,
260 .describe = dns_resolver_describe,
261 .read = dns_resolver_read,
262};
263
264static int __init init_dns_resolver(void)
265{
266 struct cred *cred;
267 struct key *keyring;
268 int ret;
269
270 /* create an override credential set with a special thread keyring in
271 * which DNS requests are cached
272 *
273 * this is used to prevent malicious redirections from being installed
274 * with add_key().
275 */
276 cred = prepare_kernel_cred(NULL);
277 if (!cred)
278 return -ENOMEM;
279
280 keyring = keyring_alloc(".dns_resolver",
281 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
282 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
283 KEY_USR_VIEW | KEY_USR_READ,
284 KEY_ALLOC_NOT_IN_QUOTA, NULL);
285 if (IS_ERR(keyring)) {
286 ret = PTR_ERR(keyring);
287 goto failed_put_cred;
288 }
289
290 ret = register_key_type(&key_type_dns_resolver);
291 if (ret < 0)
292 goto failed_put_key;
293
294 /* instruct request_key() to use this special keyring as a cache for
295 * the results it looks up */
296 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
297 cred->thread_keyring = keyring;
298 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
299 dns_resolver_cache = cred;
300
301 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
302 return 0;
303
304failed_put_key:
305 key_put(keyring);
306failed_put_cred:
307 put_cred(cred);
308 return ret;
309}
310
311static void __exit exit_dns_resolver(void)
312{
313 key_revoke(dns_resolver_cache->thread_keyring);
314 unregister_key_type(&key_type_dns_resolver);
315 put_cred(dns_resolver_cache);
316}
317
318module_init(init_dns_resolver)
319module_exit(exit_dns_resolver)
320MODULE_LICENSE("GPL");
321