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1a4240f4 WL |
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 | |
c057b190 | 22 | * along with this library; if not, see <http://www.gnu.org/licenses/>. |
1a4240f4 WL |
23 | */ |
24 | #include <linux/module.h> | |
25 | #include <linux/moduleparam.h> | |
26 | #include <linux/slab.h> | |
27 | #include <linux/string.h> | |
4b541e1f | 28 | #include <linux/ratelimit.h> |
1a4240f4 WL |
29 | #include <linux/kernel.h> |
30 | #include <linux/keyctl.h> | |
af352fe9 | 31 | #include <linux/err.h> |
4a2d7892 | 32 | #include <linux/seq_file.h> |
1a4240f4 WL |
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 | ||
95c96174 | 41 | unsigned int dns_resolver_debug; |
1a4240f4 WL |
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 | ||
4a2d7892 WL |
47 | #define DNS_ERRORNO_OPTION "dnserror" |
48 | ||
1a4240f4 | 49 | /* |
d46d4942 | 50 | * Preparse instantiation data for a dns_resolver key. |
1a4240f4 WL |
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 | |
d46d4942 | 62 | dns_resolver_preparse(struct key_preparsed_payload *prep) |
1a4240f4 WL |
63 | { |
64 | struct user_key_payload *upayload; | |
4a2d7892 | 65 | unsigned long derrno; |
1a4240f4 | 66 | int ret; |
d46d4942 | 67 | int datalen = prep->datalen, result_len = 0; |
cf7f601c | 68 | const char *data = prep->data, *end, *opt; |
1a4240f4 | 69 | |
d46d4942 | 70 | kenter("'%*.*s',%u", datalen, datalen, data, datalen); |
1a4240f4 WL |
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 */ | |
4a2d7892 | 77 | end = data + datalen; |
1a4240f4 WL |
78 | opt = memchr(data, '#', datalen); |
79 | if (!opt) { | |
4a2d7892 WL |
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 { | |
d0981217 | 90 | int opt_len, opt_nlen; |
4a2d7892 | 91 | const char *eq; |
d0981217 | 92 | char optval[128]; |
4a2d7892 WL |
93 | |
94 | next_opt = memchr(opt, '#', end - opt) ?: end; | |
95 | opt_len = next_opt - opt; | |
d0981217 | 96 | if (opt_len <= 0 || opt_len > sizeof(optval)) { |
4b541e1f EB |
97 | pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n", |
98 | opt_len); | |
4a2d7892 WL |
99 | return -EINVAL; |
100 | } | |
101 | ||
d0981217 EB |
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 | } | |
4a2d7892 | 112 | |
d0981217 EB |
113 | kdebug("option '%*.*s' val '%s'", |
114 | opt_nlen, opt_nlen, opt, optval); | |
4a2d7892 WL |
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"); | |
4a2d7892 | 121 | |
d0981217 | 122 | ret = kstrtoul(optval, 10, &derrno); |
4a2d7892 WL |
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); | |
146aa8b1 | 130 | prep->payload.data[dns_key_error] = ERR_PTR(-derrno); |
4a2d7892 WL |
131 | continue; |
132 | } | |
133 | ||
134 | bad_option_value: | |
4b541e1f EB |
135 | pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n", |
136 | opt_nlen, opt_nlen, opt); | |
4a2d7892 WL |
137 | return -EINVAL; |
138 | } while (opt = next_opt + 1, opt < end); | |
1a4240f4 WL |
139 | } |
140 | ||
4a2d7892 WL |
141 | /* don't cache the result if we're caching an error saying there's no |
142 | * result */ | |
146aa8b1 DH |
143 | if (prep->payload.data[dns_key_error]) { |
144 | kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error])); | |
4a2d7892 WL |
145 | return 0; |
146 | } | |
147 | ||
148 | kdebug("store result"); | |
d46d4942 | 149 | prep->quotalen = result_len; |
1a4240f4 WL |
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'; | |
1a4240f4 | 160 | |
146aa8b1 | 161 | prep->payload.data[dns_key_data] = upayload; |
1a4240f4 WL |
162 | kleave(" = 0"); |
163 | return 0; | |
164 | } | |
165 | ||
d46d4942 DH |
166 | /* |
167 | * Clean up the preparse data | |
168 | */ | |
169 | static void dns_resolver_free_preparse(struct key_preparsed_payload *prep) | |
170 | { | |
171 | pr_devel("==>%s()\n", __func__); | |
172 | ||
146aa8b1 | 173 | kfree(prep->payload.data[dns_key_data]); |
d46d4942 DH |
174 | } |
175 | ||
1a4240f4 WL |
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 | */ | |
0c903ab6 DH |
182 | static bool dns_resolver_cmp(const struct key *key, |
183 | const struct key_match_data *match_data) | |
1a4240f4 WL |
184 | { |
185 | int slen, dlen, ret = 0; | |
46291959 | 186 | const char *src = key->description, *dsp = match_data->raw_data; |
1a4240f4 WL |
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 | ||
c06cfb08 DH |
214 | /* |
215 | * Preparse the match criterion. | |
216 | */ | |
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 | ||
4a2d7892 WL |
224 | /* |
225 | * Describe a DNS key | |
226 | */ | |
227 | static void dns_resolver_describe(const struct key *key, struct seq_file *m) | |
228 | { | |
4a2d7892 | 229 | seq_puts(m, key->description); |
363b02da | 230 | if (key_is_positive(key)) { |
146aa8b1 DH |
231 | int err = PTR_ERR(key->payload.data[dns_key_error]); |
232 | ||
78b7280c DH |
233 | if (err) |
234 | seq_printf(m, ": %d", err); | |
235 | else | |
236 | seq_printf(m, ": %u", key->datalen); | |
237 | } | |
4a2d7892 WL |
238 | } |
239 | ||
1362fa07 DH |
240 | /* |
241 | * read the DNS data | |
242 | * - the key's semaphore is read-locked | |
243 | */ | |
244 | static long dns_resolver_read(const struct key *key, | |
245 | char __user *buffer, size_t buflen) | |
246 | { | |
146aa8b1 DH |
247 | int err = PTR_ERR(key->payload.data[dns_key_error]); |
248 | ||
249 | if (err) | |
250 | return err; | |
1362fa07 DH |
251 | |
252 | return user_read(key, buffer, buflen); | |
253 | } | |
254 | ||
1a4240f4 WL |
255 | struct key_type key_type_dns_resolver = { |
256 | .name = "dns_resolver", | |
d46d4942 DH |
257 | .preparse = dns_resolver_preparse, |
258 | .free_preparse = dns_resolver_free_preparse, | |
259 | .instantiate = generic_key_instantiate, | |
c06cfb08 | 260 | .match_preparse = dns_resolver_match_preparse, |
1a4240f4 WL |
261 | .revoke = user_revoke, |
262 | .destroy = user_destroy, | |
4a2d7892 | 263 | .describe = dns_resolver_describe, |
1362fa07 | 264 | .read = dns_resolver_read, |
1a4240f4 WL |
265 | }; |
266 | ||
267 | static int __init init_dns_resolver(void) | |
268 | { | |
269 | struct cred *cred; | |
270 | struct key *keyring; | |
271 | int ret; | |
272 | ||
1a4240f4 WL |
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 | ||
2a74dbb9 LT |
283 | keyring = keyring_alloc(".dns_resolver", |
284 | GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, | |
f8aa23a5 DH |
285 | (KEY_POS_ALL & ~KEY_POS_SETATTR) | |
286 | KEY_USR_VIEW | KEY_USR_READ, | |
5ac7eace | 287 | KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); |
1a4240f4 WL |
288 | if (IS_ERR(keyring)) { |
289 | ret = PTR_ERR(keyring); | |
290 | goto failed_put_cred; | |
291 | } | |
292 | ||
1a4240f4 WL |
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 */ | |
700920eb | 299 | set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags); |
1a4240f4 WL |
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 | ||
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); | |
1a4240f4 WL |
319 | } |
320 | ||
321 | module_init(init_dns_resolver) | |
322 | module_exit(exit_dns_resolver) | |
323 | MODULE_LICENSE("GPL"); | |
f8aa23a5 | 324 |