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/ratelimit.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
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, S_IWUSR | S_IRUGO);
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 * 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 */
61 static int
dns_resolver_preparse(struct key_preparsed_payload * prep)62 dns_resolver_preparse(struct key_preparsed_payload *prep)
63 {
64 struct user_key_payload *upayload;
65 unsigned long derrno;
66 int ret;
67 int datalen = prep->datalen, result_len = 0;
68 const char *data = prep->data, *end, *opt;
69
70 kenter("'%*.*s',%u", datalen, datalen, data, datalen);
71
72 if (datalen <= 1 || !data || data[datalen - 1] != '\0')
73 return -EINVAL;
74 datalen--;
75
76 /* deal with any options embedded in the data */
77 end = data + datalen;
78 opt = memchr(data, '#', datalen);
79 if (!opt) {
80 /* no options: the entire data is the result */
81 kdebug("no options");
82 result_len = datalen;
83 } else {
84 const char *next_opt;
85
86 result_len = opt - data;
87 opt++;
88 kdebug("options: '%s'", opt);
89 do {
90 int opt_len, opt_nlen;
91 const char *eq;
92 char optval[128];
93
94 next_opt = memchr(opt, '#', end - opt) ?: end;
95 opt_len = next_opt - opt;
96 if (opt_len <= 0 || opt_len > sizeof(optval)) {
97 pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
98 opt_len);
99 return -EINVAL;
100 }
101
102 eq = memchr(opt, '=', opt_len);
103 if (eq) {
104 opt_nlen = eq - opt;
105 eq++;
106 memcpy(optval, eq, next_opt - eq);
107 optval[next_opt - eq] = '\0';
108 } else {
109 opt_nlen = opt_len;
110 optval[0] = '\0';
111 }
112
113 kdebug("option '%*.*s' val '%s'",
114 opt_nlen, opt_nlen, opt, optval);
115
116 /* see if it's an error number representing a DNS error
117 * that's to be recorded as the result in this key */
118 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
119 memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
120 kdebug("dns error number option");
121
122 ret = kstrtoul(optval, 10, &derrno);
123 if (ret < 0)
124 goto bad_option_value;
125
126 if (derrno < 1 || derrno > 511)
127 goto bad_option_value;
128
129 kdebug("dns error no. = %lu", derrno);
130 prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
131 continue;
132 }
133
134 bad_option_value:
135 pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
136 opt_nlen, opt_nlen, opt);
137 return -EINVAL;
138 } while (opt = next_opt + 1, opt < end);
139 }
140
141 /* don't cache the result if we're caching an error saying there's no
142 * result */
143 if (prep->payload.data[dns_key_error]) {
144 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
145 return 0;
146 }
147
148 kdebug("store result");
149 prep->quotalen = result_len;
150
151 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
152 if (!upayload) {
153 kleave(" = -ENOMEM");
154 return -ENOMEM;
155 }
156
157 upayload->datalen = result_len;
158 memcpy(upayload->data, data, result_len);
159 upayload->data[result_len] = '\0';
160
161 prep->payload.data[dns_key_data] = upayload;
162 kleave(" = 0");
163 return 0;
164 }
165
166 /*
167 * Clean up the preparse data
168 */
dns_resolver_free_preparse(struct key_preparsed_payload * prep)169 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
170 {
171 pr_devel("==>%s()\n", __func__);
172
173 kfree(prep->payload.data[dns_key_data]);
174 }
175
176 /*
177 * The description is of the form "[<type>:]<domain_name>"
178 *
179 * The domain name may be a simple name or an absolute domain name (which
180 * should end with a period). The domain name is case-independent.
181 */
dns_resolver_cmp(const struct key * key,const struct key_match_data * match_data)182 static bool dns_resolver_cmp(const struct key *key,
183 const struct key_match_data *match_data)
184 {
185 int slen, dlen, ret = 0;
186 const char *src = key->description, *dsp = match_data->raw_data;
187
188 kenter("%s,%s", src, dsp);
189
190 if (!src || !dsp)
191 goto no_match;
192
193 if (strcasecmp(src, dsp) == 0)
194 goto matched;
195
196 slen = strlen(src);
197 dlen = strlen(dsp);
198 if (slen <= 0 || dlen <= 0)
199 goto no_match;
200 if (src[slen - 1] == '.')
201 slen--;
202 if (dsp[dlen - 1] == '.')
203 dlen--;
204 if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
205 goto no_match;
206
207 matched:
208 ret = 1;
209 no_match:
210 kleave(" = %d", ret);
211 return ret;
212 }
213
214 /*
215 * Preparse the match criterion.
216 */
dns_resolver_match_preparse(struct key_match_data * match_data)217 static int dns_resolver_match_preparse(struct key_match_data *match_data)
218 {
219 match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
220 match_data->cmp = dns_resolver_cmp;
221 return 0;
222 }
223
224 /*
225 * Describe a DNS key
226 */
dns_resolver_describe(const struct key * key,struct seq_file * m)227 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
228 {
229 seq_puts(m, key->description);
230 if (key_is_positive(key)) {
231 int err = PTR_ERR(key->payload.data[dns_key_error]);
232
233 if (err)
234 seq_printf(m, ": %d", err);
235 else
236 seq_printf(m, ": %u", key->datalen);
237 }
238 }
239
240 /*
241 * read the DNS data
242 * - the key's semaphore is read-locked
243 */
dns_resolver_read(const struct key * key,char __user * buffer,size_t buflen)244 static long dns_resolver_read(const struct key *key,
245 char __user *buffer, size_t buflen)
246 {
247 int err = PTR_ERR(key->payload.data[dns_key_error]);
248
249 if (err)
250 return err;
251
252 return user_read(key, buffer, buflen);
253 }
254
255 struct key_type key_type_dns_resolver = {
256 .name = "dns_resolver",
257 .preparse = dns_resolver_preparse,
258 .free_preparse = dns_resolver_free_preparse,
259 .instantiate = generic_key_instantiate,
260 .match_preparse = dns_resolver_match_preparse,
261 .revoke = user_revoke,
262 .destroy = user_destroy,
263 .describe = dns_resolver_describe,
264 .read = dns_resolver_read,
265 };
266
init_dns_resolver(void)267 static int __init init_dns_resolver(void)
268 {
269 struct cred *cred;
270 struct key *keyring;
271 int ret;
272
273 /* create an override credential set with a special thread keyring in
274 * which DNS requests are cached
275 *
276 * this is used to prevent malicious redirections from being installed
277 * with add_key().
278 */
279 cred = prepare_kernel_cred(NULL);
280 if (!cred)
281 return -ENOMEM;
282
283 keyring = keyring_alloc(".dns_resolver",
284 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
285 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
286 KEY_USR_VIEW | KEY_USR_READ,
287 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
288 if (IS_ERR(keyring)) {
289 ret = PTR_ERR(keyring);
290 goto failed_put_cred;
291 }
292
293 ret = register_key_type(&key_type_dns_resolver);
294 if (ret < 0)
295 goto failed_put_key;
296
297 /* instruct request_key() to use this special keyring as a cache for
298 * the results it looks up */
299 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
300 cred->thread_keyring = keyring;
301 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
302 dns_resolver_cache = cred;
303
304 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
305 return 0;
306
307 failed_put_key:
308 key_put(keyring);
309 failed_put_cred:
310 put_cred(cred);
311 return ret;
312 }
313
exit_dns_resolver(void)314 static void __exit exit_dns_resolver(void)
315 {
316 key_revoke(dns_resolver_cache->thread_keyring);
317 unregister_key_type(&key_type_dns_resolver);
318 put_cred(dns_resolver_cache);
319 }
320
321 module_init(init_dns_resolver)
322 module_exit(exit_dns_resolver)
323 MODULE_LICENSE("GPL");
324
325