1 /* Key type used to cache DNS lookups made by the kernel
3 * See Documentation/networking/dns_resolver.txt
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)
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.
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.
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/>.
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>
37 MODULE_DESCRIPTION("DNS Resolver");
38 MODULE_AUTHOR("Wang Lei");
39 MODULE_LICENSE("GPL");
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");
45 const struct cred *dns_resolver_cache;
47 #define DNS_ERRORNO_OPTION "dnserror"
50 * Preparse instantiation data for a dns_resolver key.
52 * The data must be a NUL-terminated string, with the NUL char accounted in
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:
59 * "ip1,ip2,...#foo=bar"
62 dns_resolver_preparse(struct key_preparsed_payload *prep)
64 struct user_key_payload *upayload;
67 int datalen = prep->datalen, result_len = 0;
68 const char *data = prep->data, *end, *opt;
70 kenter("'%*.*s',%u", datalen, datalen, data, datalen);
72 if (datalen <= 1 || !data || data[datalen - 1] != '\0')
76 /* deal with any options embedded in the data */
78 opt = memchr(data, '#', datalen);
80 /* no options: the entire data is the result */
86 result_len = opt - data;
88 kdebug("options: '%s'", opt);
90 int opt_len, opt_nlen;
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",
102 eq = memchr(opt, '=', opt_len);
106 memcpy(optval, eq, next_opt - eq);
107 optval[next_opt - eq] = '\0';
113 kdebug("option '%*.*s' val '%s'",
114 opt_nlen, opt_nlen, opt, optval);
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");
122 ret = kstrtoul(optval, 10, &derrno);
124 goto bad_option_value;
126 if (derrno < 1 || derrno > 511)
127 goto bad_option_value;
129 kdebug("dns error no. = %lu", derrno);
130 prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
135 pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
136 opt_nlen, opt_nlen, opt);
138 } while (opt = next_opt + 1, opt < end);
141 /* don't cache the result if we're caching an error saying there's no
143 if (prep->payload.data[dns_key_error]) {
144 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
148 kdebug("store result");
149 prep->quotalen = result_len;
151 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
153 kleave(" = -ENOMEM");
157 upayload->datalen = result_len;
158 memcpy(upayload->data, data, result_len);
159 upayload->data[result_len] = '\0';
161 prep->payload.data[dns_key_data] = upayload;
167 * Clean up the preparse data
169 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
171 pr_devel("==>%s()\n", __func__);
173 kfree(prep->payload.data[dns_key_data]);
177 * The description is of the form "[<type>:]<domain_name>"
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.
182 static bool dns_resolver_cmp(const struct key *key,
183 const struct key_match_data *match_data)
185 int slen, dlen, ret = 0;
186 const char *src = key->description, *dsp = match_data->raw_data;
188 kenter("%s,%s", src, dsp);
193 if (strcasecmp(src, dsp) == 0)
198 if (slen <= 0 || dlen <= 0)
200 if (src[slen - 1] == '.')
202 if (dsp[dlen - 1] == '.')
204 if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
210 kleave(" = %d", ret);
215 * Preparse the match criterion.
217 static int dns_resolver_match_preparse(struct key_match_data *match_data)
219 match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
220 match_data->cmp = dns_resolver_cmp;
227 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
229 seq_puts(m, key->description);
230 if (key_is_positive(key)) {
231 int err = PTR_ERR(key->payload.data[dns_key_error]);
234 seq_printf(m, ": %d", err);
236 seq_printf(m, ": %u", key->datalen);
242 * - the key's semaphore is read-locked
244 static long dns_resolver_read(const struct key *key,
245 char *buffer, size_t buflen)
247 int err = PTR_ERR(key->payload.data[dns_key_error]);
252 return user_read(key, buffer, buflen);
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,
267 static int __init init_dns_resolver(void)
273 /* create an override credential set with a special thread keyring in
274 * which DNS requests are cached
276 * this is used to prevent malicious redirections from being installed
279 cred = prepare_kernel_cred(NULL);
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;
293 ret = register_key_type(&key_type_dns_resolver);
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;
304 kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
314 static void __exit exit_dns_resolver(void)
316 key_revoke(dns_resolver_cache->thread_keyring);
317 unregister_key_type(&key_type_dns_resolver);
318 put_cred(dns_resolver_cache);
321 module_init(init_dns_resolver)
322 module_exit(exit_dns_resolver)
323 MODULE_LICENSE("GPL");