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
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, 0644);
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 * 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 */
91static int
92dns_resolver_preparse(struct key_preparsed_payload *prep)
93{
94 const struct dns_payload_header *bin;
95 struct user_key_payload *upayload;
96 unsigned long derrno;
97 int ret;
98 int datalen = prep->datalen, result_len = 0;
99 const char *data = prep->data, *end, *opt;
100
101 if (datalen <= 1 || !data)
102 return -EINVAL;
103
104 if (data[0] == 0) {
105 /* It may be a server list. */
106 if (datalen <= sizeof(*bin))
107 return -EINVAL;
108
109 bin = (const struct dns_payload_header *)data;
110 kenter("[%u,%u],%u", bin->content, bin->version, datalen);
111 if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
112 pr_warn_ratelimited(
113 "dns_resolver: Unsupported content type (%u)\n",
114 bin->content);
115 return -EINVAL;
116 }
117
118 if (bin->version != 1) {
119 pr_warn_ratelimited(
120 "dns_resolver: Unsupported server list version (%u)\n",
121 bin->version);
122 return -EINVAL;
123 }
124
125 result_len = datalen;
126 goto store_result;
127 }
128
129 kenter("'%*.*s',%u", datalen, datalen, data, datalen);
130
131 if (!data || data[datalen - 1] != '\0')
132 return -EINVAL;
133 datalen--;
134
135 /* deal with any options embedded in the data */
136 end = data + datalen;
137 opt = memchr(p: data, c: '#', size: datalen);
138 if (!opt) {
139 /* no options: the entire data is the result */
140 kdebug("no options");
141 result_len = datalen;
142 } else {
143 const char *next_opt;
144
145 result_len = opt - data;
146 opt++;
147 kdebug("options: '%s'", opt);
148 do {
149 int opt_len, opt_nlen;
150 const char *eq;
151 char optval[128];
152
153 next_opt = memchr(p: opt, c: '#', size: end - opt) ?: end;
154 opt_len = next_opt - opt;
155 if (opt_len <= 0 || opt_len > sizeof(optval)) {
156 pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
157 opt_len);
158 return -EINVAL;
159 }
160
161 eq = memchr(p: opt, c: '=', size: opt_len);
162 if (eq) {
163 opt_nlen = eq - opt;
164 eq++;
165 memcpy(optval, eq, next_opt - eq);
166 optval[next_opt - eq] = '\0';
167 } else {
168 opt_nlen = opt_len;
169 optval[0] = '\0';
170 }
171
172 kdebug("option '%*.*s' val '%s'",
173 opt_nlen, opt_nlen, opt, optval);
174
175 /* see if it's an error number representing a DNS error
176 * that's to be recorded as the result in this key */
177 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
178 memcmp(p: opt, DNS_ERRORNO_OPTION, size: opt_nlen) == 0) {
179 kdebug("dns error number option");
180
181 ret = kstrtoul(s: optval, base: 10, res: &derrno);
182 if (ret < 0)
183 goto bad_option_value;
184
185 if (derrno < 1 || derrno > 511)
186 goto bad_option_value;
187
188 kdebug("dns error no. = %lu", derrno);
189 prep->payload.data[dns_key_error] = ERR_PTR(error: -derrno);
190 continue;
191 }
192
193 bad_option_value:
194 pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
195 opt_nlen, opt_nlen, opt);
196 return -EINVAL;
197 } while (opt = next_opt + 1, opt < end);
198 }
199
200 /* don't cache the result if we're caching an error saying there's no
201 * result */
202 if (prep->payload.data[dns_key_error]) {
203 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
204 return 0;
205 }
206
207store_result:
208 kdebug("store result");
209 prep->quotalen = result_len;
210
211 upayload = kmalloc(size: sizeof(*upayload) + result_len + 1, GFP_KERNEL);
212 if (!upayload) {
213 kleave(" = -ENOMEM");
214 return -ENOMEM;
215 }
216
217 upayload->datalen = result_len;
218 memcpy(upayload->data, data, result_len);
219 upayload->data[result_len] = '\0';
220
221 prep->payload.data[dns_key_data] = upayload;
222 kleave(" = 0");
223 return 0;
224}
225
226/*
227 * Clean up the preparse data
228 */
229static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
230{
231 pr_devel("==>%s()\n", __func__);
232
233 kfree(objp: prep->payload.data[dns_key_data]);
234}
235
236/*
237 * The description is of the form "[<type>:]<domain_name>"
238 *
239 * The domain name may be a simple name or an absolute domain name (which
240 * should end with a period). The domain name is case-independent.
241 */
242static bool dns_resolver_cmp(const struct key *key,
243 const struct key_match_data *match_data)
244{
245 int slen, dlen, ret = 0;
246 const char *src = key->description, *dsp = match_data->raw_data;
247
248 kenter("%s,%s", src, dsp);
249
250 if (!src || !dsp)
251 goto no_match;
252
253 if (strcasecmp(s1: src, s2: dsp) == 0)
254 goto matched;
255
256 slen = strlen(src);
257 dlen = strlen(dsp);
258 if (slen <= 0 || dlen <= 0)
259 goto no_match;
260 if (src[slen - 1] == '.')
261 slen--;
262 if (dsp[dlen - 1] == '.')
263 dlen--;
264 if (slen != dlen || strncasecmp(s1: src, s2: dsp, n: slen) != 0)
265 goto no_match;
266
267matched:
268 ret = 1;
269no_match:
270 kleave(" = %d", ret);
271 return ret;
272}
273
274/*
275 * Preparse the match criterion.
276 */
277static int dns_resolver_match_preparse(struct key_match_data *match_data)
278{
279 match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
280 match_data->cmp = dns_resolver_cmp;
281 return 0;
282}
283
284/*
285 * Describe a DNS key
286 */
287static void dns_resolver_describe(const struct key *key, struct seq_file *m)
288{
289 seq_puts(m, s: key->description);
290 if (key_is_positive(key)) {
291 int err = PTR_ERR(ptr: key->payload.data[dns_key_error]);
292
293 if (err)
294 seq_printf(m, fmt: ": %d", err);
295 else
296 seq_printf(m, fmt: ": %u", key->datalen);
297 }
298}
299
300/*
301 * read the DNS data
302 * - the key's semaphore is read-locked
303 */
304static long dns_resolver_read(const struct key *key,
305 char *buffer, size_t buflen)
306{
307 int err = PTR_ERR(ptr: key->payload.data[dns_key_error]);
308
309 if (err)
310 return err;
311
312 return user_read(key, buffer, buflen);
313}
314
315struct key_type key_type_dns_resolver = {
316 .name = "dns_resolver",
317 .flags = KEY_TYPE_NET_DOMAIN,
318 .preparse = dns_resolver_preparse,
319 .free_preparse = dns_resolver_free_preparse,
320 .instantiate = generic_key_instantiate,
321 .match_preparse = dns_resolver_match_preparse,
322 .revoke = user_revoke,
323 .destroy = user_destroy,
324 .describe = dns_resolver_describe,
325 .read = dns_resolver_read,
326};
327
328static int __init init_dns_resolver(void)
329{
330 struct cred *cred;
331 struct key *keyring;
332 int ret;
333
334 /* create an override credential set with a special thread keyring in
335 * which DNS requests are cached
336 *
337 * this is used to prevent malicious redirections from being installed
338 * with add_key().
339 */
340 cred = prepare_kernel_cred(&init_task);
341 if (!cred)
342 return -ENOMEM;
343
344 keyring = keyring_alloc(description: ".dns_resolver",
345 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
346 perm: (KEY_POS_ALL & ~KEY_POS_SETATTR) |
347 KEY_USR_VIEW | KEY_USR_READ,
348 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
349 if (IS_ERR(keyring)) {
350 ret = PTR_ERR(keyring);
351 goto failed_put_cred;
352 }
353
354 ret = register_key_type(&key_type_dns_resolver);
355 if (ret < 0)
356 goto failed_put_key;
357
358 /* instruct request_key() to use this special keyring as a cache for
359 * the results it looks up */
360 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
361 cred->thread_keyring = keyring;
362 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
363 dns_resolver_cache = cred;
364
365 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
366 return 0;
367
368failed_put_key:
369 key_put(keyring);
370failed_put_cred:
371 put_cred(cred);
372 return ret;
373}
374
375static void __exit exit_dns_resolver(void)
376{
377 key_revoke(key: dns_resolver_cache->thread_keyring);
378 unregister_key_type(ktype: &key_type_dns_resolver);
379 put_cred(cred: dns_resolver_cache);
380}
381
382module_init(init_dns_resolver)
383module_exit(exit_dns_resolver)
384MODULE_LICENSE("GPL");
385

source code of linux/net/dns_resolver/dns_key.c