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 |
92 | dns_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 | |
207 | store_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 | */ |
229 | static 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 | */ |
242 | static 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 | |
267 | matched: |
268 | ret = 1; |
269 | no_match: |
270 | kleave(" = %d" , ret); |
271 | return ret; |
272 | } |
273 | |
274 | /* |
275 | * Preparse the match criterion. |
276 | */ |
277 | static 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 | */ |
287 | static 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 | */ |
304 | static 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 | |
315 | struct 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 | |
328 | static 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 | |
368 | failed_put_key: |
369 | key_put(keyring); |
370 | failed_put_cred: |
371 | put_cred(cred); |
372 | return ret; |
373 | } |
374 | |
375 | static 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 | |
382 | module_init(init_dns_resolver) |
383 | module_exit(exit_dns_resolver) |
384 | MODULE_LICENSE("GPL" ); |
385 | |