1 /* Key type used to cache DNS lookups made by the kernel
2 *
3 * See Documentation/networking/dns_resolver.rst
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 <linux/dns_resolver.h>
33 #include <keys/dns_resolver-type.h>
34 #include <keys/user-type.h>
35 #include "internal.h"
36
37 MODULE_DESCRIPTION("DNS Resolver");
38 MODULE_AUTHOR("Wang Lei");
39 MODULE_LICENSE("GPL");
40
41 unsigned int dns_resolver_debug;
42 module_param_named(debug, dns_resolver_debug, uint, 0644);
43 MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
44
45 const struct cred *dns_resolver_cache;
46
47 #define DNS_ERRORNO_OPTION "dnserror"
48
49 /*
50 * Preparse instantiation data for a dns_resolver key.
51 *
52 * For normal hostname lookups, the data must be a NUL-terminated string, with
53 * the NUL char accounted in 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 *
61 * For server list requests, the data must begin with a NUL char and be
62 * followed by a byte indicating the version of the data format. Version 1
63 * looks something like (note this is packed):
64 *
65 * u8 Non-string marker (ie. 0)
66 * u8 Content (DNS_PAYLOAD_IS_*)
67 * u8 Version (e.g. 1)
68 * u8 Source of server list
69 * u8 Lookup status of server list
70 * u8 Number of servers
71 * foreach-server {
72 * __le16 Name length
73 * __le16 Priority (as per SRV record, low first)
74 * __le16 Weight (as per SRV record, higher first)
75 * __le16 Port
76 * u8 Source of address list
77 * u8 Lookup status of address list
78 * u8 Protocol (DNS_SERVER_PROTOCOL_*)
79 * u8 Number of addresses
80 * char[] Name (not NUL-terminated)
81 * foreach-address {
82 * u8 Family (DNS_ADDRESS_IS_*)
83 * union {
84 * u8[4] ipv4_addr
85 * u8[16] ipv6_addr
86 * }
87 * }
88 * }
89 *
90 */
91 static int
dns_resolver_preparse(struct key_preparsed_payload * prep)92 dns_resolver_preparse(struct key_preparsed_payload *prep)
93 {
94 struct user_key_payload *upayload;
95 unsigned long derrno;
96 int ret;
97 int datalen = prep->datalen, result_len = 0;
98 const char *data = prep->data, *end, *opt;
99
100 if (datalen <= 1 || !data)
101 return -EINVAL;
102
103 if (data[0] == 0) {
104 const struct dns_server_list_v1_header *v1;
105
106 /* It may be a server list. */
107 if (datalen < sizeof(*v1))
108 return -EINVAL;
109
110 v1 = (const struct dns_server_list_v1_header *)data;
111 kenter("[%u,%u],%u", v1->hdr.content, v1->hdr.version, datalen);
112 if (v1->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST) {
113 pr_warn_ratelimited(
114 "dns_resolver: Unsupported content type (%u)\n",
115 v1->hdr.content);
116 return -EINVAL;
117 }
118
119 if (v1->hdr.version != 1) {
120 pr_warn_ratelimited(
121 "dns_resolver: Unsupported server list version (%u)\n",
122 v1->hdr.version);
123 return -EINVAL;
124 }
125
126 if ((v1->status != DNS_LOOKUP_GOOD &&
127 v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
128 if (prep->expiry == TIME64_MAX)
129 prep->expiry = ktime_get_real_seconds() + 1;
130 }
131
132 result_len = datalen;
133 goto store_result;
134 }
135
136 kenter("'%*.*s',%u", datalen, datalen, data, datalen);
137
138 if (!data || data[datalen - 1] != '\0')
139 return -EINVAL;
140 datalen--;
141
142 /* deal with any options embedded in the data */
143 end = data + datalen;
144 opt = memchr(data, '#', datalen);
145 if (!opt) {
146 /* no options: the entire data is the result */
147 kdebug("no options");
148 result_len = datalen;
149 } else {
150 const char *next_opt;
151
152 result_len = opt - data;
153 opt++;
154 kdebug("options: '%s'", opt);
155 do {
156 int opt_len, opt_nlen;
157 const char *eq;
158 char optval[128];
159
160 next_opt = memchr(opt, '#', end - opt) ?: end;
161 opt_len = next_opt - opt;
162 if (opt_len <= 0 || opt_len > sizeof(optval)) {
163 pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
164 opt_len);
165 return -EINVAL;
166 }
167
168 eq = memchr(opt, '=', opt_len);
169 if (eq) {
170 opt_nlen = eq - opt;
171 eq++;
172 memcpy(optval, eq, next_opt - eq);
173 optval[next_opt - eq] = '\0';
174 } else {
175 opt_nlen = opt_len;
176 optval[0] = '\0';
177 }
178
179 kdebug("option '%*.*s' val '%s'",
180 opt_nlen, opt_nlen, opt, optval);
181
182 /* see if it's an error number representing a DNS error
183 * that's to be recorded as the result in this key */
184 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
185 memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
186 kdebug("dns error number option");
187
188 ret = kstrtoul(optval, 10, &derrno);
189 if (ret < 0)
190 goto bad_option_value;
191
192 if (derrno < 1 || derrno > 511)
193 goto bad_option_value;
194
195 kdebug("dns error no. = %lu", derrno);
196 prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
197 continue;
198 }
199
200 bad_option_value:
201 pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
202 opt_nlen, opt_nlen, opt);
203 return -EINVAL;
204 } while (opt = next_opt + 1, opt < end);
205 }
206
207 /* don't cache the result if we're caching an error saying there's no
208 * result */
209 if (prep->payload.data[dns_key_error]) {
210 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
211 return 0;
212 }
213
214 store_result:
215 kdebug("store result");
216 prep->quotalen = result_len;
217
218 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
219 if (!upayload) {
220 kleave(" = -ENOMEM");
221 return -ENOMEM;
222 }
223
224 upayload->datalen = result_len;
225 memcpy(upayload->data, data, result_len);
226 upayload->data[result_len] = '\0';
227
228 prep->payload.data[dns_key_data] = upayload;
229 kleave(" = 0");
230 return 0;
231 }
232
233 /*
234 * Clean up the preparse data
235 */
dns_resolver_free_preparse(struct key_preparsed_payload * prep)236 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
237 {
238 pr_devel("==>%s()\n", __func__);
239
240 kfree(prep->payload.data[dns_key_data]);
241 }
242
243 /*
244 * The description is of the form "[<type>:]<domain_name>"
245 *
246 * The domain name may be a simple name or an absolute domain name (which
247 * should end with a period). The domain name is case-independent.
248 */
dns_resolver_cmp(const struct key * key,const struct key_match_data * match_data)249 static bool dns_resolver_cmp(const struct key *key,
250 const struct key_match_data *match_data)
251 {
252 int slen, dlen, ret = 0;
253 const char *src = key->description, *dsp = match_data->raw_data;
254
255 kenter("%s,%s", src, dsp);
256
257 if (!src || !dsp)
258 goto no_match;
259
260 if (strcasecmp(src, dsp) == 0)
261 goto matched;
262
263 slen = strlen(src);
264 dlen = strlen(dsp);
265 if (slen <= 0 || dlen <= 0)
266 goto no_match;
267 if (src[slen - 1] == '.')
268 slen--;
269 if (dsp[dlen - 1] == '.')
270 dlen--;
271 if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
272 goto no_match;
273
274 matched:
275 ret = 1;
276 no_match:
277 kleave(" = %d", ret);
278 return ret;
279 }
280
281 /*
282 * Preparse the match criterion.
283 */
dns_resolver_match_preparse(struct key_match_data * match_data)284 static int dns_resolver_match_preparse(struct key_match_data *match_data)
285 {
286 match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
287 match_data->cmp = dns_resolver_cmp;
288 return 0;
289 }
290
291 /*
292 * Describe a DNS key
293 */
dns_resolver_describe(const struct key * key,struct seq_file * m)294 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
295 {
296 seq_puts(m, key->description);
297 if (key_is_positive(key)) {
298 int err = PTR_ERR(key->payload.data[dns_key_error]);
299
300 if (err)
301 seq_printf(m, ": %d", err);
302 else
303 seq_printf(m, ": %u", key->datalen);
304 }
305 }
306
307 /*
308 * read the DNS data
309 * - the key's semaphore is read-locked
310 */
dns_resolver_read(const struct key * key,char * buffer,size_t buflen)311 static long dns_resolver_read(const struct key *key,
312 char *buffer, size_t buflen)
313 {
314 int err = PTR_ERR(key->payload.data[dns_key_error]);
315
316 if (err)
317 return err;
318
319 return user_read(key, buffer, buflen);
320 }
321
322 struct key_type key_type_dns_resolver = {
323 .name = "dns_resolver",
324 .flags = KEY_TYPE_NET_DOMAIN | KEY_TYPE_INSTANT_REAP,
325 .preparse = dns_resolver_preparse,
326 .free_preparse = dns_resolver_free_preparse,
327 .instantiate = generic_key_instantiate,
328 .match_preparse = dns_resolver_match_preparse,
329 .revoke = user_revoke,
330 .destroy = user_destroy,
331 .describe = dns_resolver_describe,
332 .read = dns_resolver_read,
333 };
334
init_dns_resolver(void)335 static int __init init_dns_resolver(void)
336 {
337 struct cred *cred;
338 struct key *keyring;
339 int ret;
340
341 /* create an override credential set with a special thread keyring in
342 * which DNS requests are cached
343 *
344 * this is used to prevent malicious redirections from being installed
345 * with add_key().
346 */
347 cred = prepare_kernel_cred(&init_task);
348 if (!cred)
349 return -ENOMEM;
350
351 keyring = keyring_alloc(".dns_resolver",
352 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
353 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
354 KEY_USR_VIEW | KEY_USR_READ,
355 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
356 if (IS_ERR(keyring)) {
357 ret = PTR_ERR(keyring);
358 goto failed_put_cred;
359 }
360
361 ret = register_key_type(&key_type_dns_resolver);
362 if (ret < 0)
363 goto failed_put_key;
364
365 /* instruct request_key() to use this special keyring as a cache for
366 * the results it looks up */
367 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
368 cred->thread_keyring = keyring;
369 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
370 dns_resolver_cache = cred;
371
372 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
373 return 0;
374
375 failed_put_key:
376 key_put(keyring);
377 failed_put_cred:
378 put_cred(cred);
379 return ret;
380 }
381
exit_dns_resolver(void)382 static void __exit exit_dns_resolver(void)
383 {
384 key_revoke(dns_resolver_cache->thread_keyring);
385 unregister_key_type(&key_type_dns_resolver);
386 put_cred(dns_resolver_cache);
387 }
388
389 module_init(init_dns_resolver)
390 module_exit(exit_dns_resolver)
391 MODULE_LICENSE("GPL");
392