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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> | |
28 | #include <linux/kernel.h> | |
29 | #include <linux/keyctl.h> | |
af352fe9 | 30 | #include <linux/err.h> |
4a2d7892 | 31 | #include <linux/seq_file.h> |
1a4240f4 WL |
32 | #include <keys/dns_resolver-type.h> |
33 | #include <keys/user-type.h> | |
34 | #include "internal.h" | |
35 | ||
36 | MODULE_DESCRIPTION("DNS Resolver"); | |
37 | MODULE_AUTHOR("Wang Lei"); | |
38 | MODULE_LICENSE("GPL"); | |
39 | ||
95c96174 | 40 | unsigned int dns_resolver_debug; |
1a4240f4 WL |
41 | module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO); |
42 | MODULE_PARM_DESC(debug, "DNS Resolver debugging mask"); | |
43 | ||
44 | const struct cred *dns_resolver_cache; | |
45 | ||
4a2d7892 WL |
46 | #define DNS_ERRORNO_OPTION "dnserror" |
47 | ||
1a4240f4 WL |
48 | /* |
49 | * Instantiate a user defined key for dns_resolver. | |
50 | * | |
51 | * The data must be a NUL-terminated string, with the NUL char accounted in | |
52 | * datalen. | |
53 | * | |
54 | * If the data contains a '#' characters, then we take the clause after each | |
55 | * one to be an option of the form 'key=value'. The actual data of interest is | |
56 | * the string leading up to the first '#'. For instance: | |
57 | * | |
58 | * "ip1,ip2,...#foo=bar" | |
59 | */ | |
60 | static int | |
cf7f601c | 61 | dns_resolver_instantiate(struct key *key, struct key_preparsed_payload *prep) |
1a4240f4 WL |
62 | { |
63 | struct user_key_payload *upayload; | |
4a2d7892 | 64 | unsigned long derrno; |
1a4240f4 | 65 | int ret; |
cf7f601c DH |
66 | size_t datalen = prep->datalen, result_len = 0; |
67 | const char *data = prep->data, *end, *opt; | |
1a4240f4 | 68 | |
1362fa07 DH |
69 | kenter("%%%d,%s,'%*.*s',%zu", |
70 | key->serial, key->description, | |
71 | (int)datalen, (int)datalen, data, datalen); | |
1a4240f4 WL |
72 | |
73 | if (datalen <= 1 || !data || data[datalen - 1] != '\0') | |
74 | return -EINVAL; | |
75 | datalen--; | |
76 | ||
77 | /* deal with any options embedded in the data */ | |
4a2d7892 | 78 | end = data + datalen; |
1a4240f4 WL |
79 | opt = memchr(data, '#', datalen); |
80 | if (!opt) { | |
4a2d7892 WL |
81 | /* no options: the entire data is the result */ |
82 | kdebug("no options"); | |
83 | result_len = datalen; | |
84 | } else { | |
85 | const char *next_opt; | |
86 | ||
87 | result_len = opt - data; | |
88 | opt++; | |
89 | kdebug("options: '%s'", opt); | |
90 | do { | |
91 | const char *eq; | |
92 | int opt_len, opt_nlen, opt_vlen, tmp; | |
93 | ||
94 | next_opt = memchr(opt, '#', end - opt) ?: end; | |
95 | opt_len = next_opt - opt; | |
96 | if (!opt_len) { | |
97 | printk(KERN_WARNING | |
98 | "Empty option to dns_resolver key %d\n", | |
99 | key->serial); | |
100 | return -EINVAL; | |
101 | } | |
102 | ||
103 | eq = memchr(opt, '=', opt_len) ?: end; | |
104 | opt_nlen = eq - opt; | |
105 | eq++; | |
106 | opt_vlen = next_opt - eq; /* will be -1 if no value */ | |
107 | ||
108 | tmp = opt_vlen >= 0 ? opt_vlen : 0; | |
109 | kdebug("option '%*.*s' val '%*.*s'", | |
110 | opt_nlen, opt_nlen, opt, tmp, tmp, eq); | |
111 | ||
112 | /* see if it's an error number representing a DNS error | |
113 | * that's to be recorded as the result in this key */ | |
114 | if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 && | |
115 | memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) { | |
116 | kdebug("dns error number option"); | |
117 | if (opt_vlen <= 0) | |
118 | goto bad_option_value; | |
119 | ||
92338dc2 | 120 | ret = kstrtoul(eq, 10, &derrno); |
4a2d7892 WL |
121 | if (ret < 0) |
122 | goto bad_option_value; | |
123 | ||
124 | if (derrno < 1 || derrno > 511) | |
125 | goto bad_option_value; | |
126 | ||
127 | kdebug("dns error no. = %lu", derrno); | |
128 | key->type_data.x[0] = -derrno; | |
129 | continue; | |
130 | } | |
131 | ||
132 | bad_option_value: | |
133 | printk(KERN_WARNING | |
134 | "Option '%*.*s' to dns_resolver key %d:" | |
135 | " bad/missing value\n", | |
136 | opt_nlen, opt_nlen, opt, key->serial); | |
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 */ | |
143 | if (key->type_data.x[0]) { | |
144 | kleave(" = 0 [h_error %ld]", key->type_data.x[0]); | |
145 | return 0; | |
146 | } | |
147 | ||
148 | kdebug("store result"); | |
1a4240f4 WL |
149 | ret = key_payload_reserve(key, result_len); |
150 | if (ret < 0) | |
151 | return -EINVAL; | |
152 | ||
153 | upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL); | |
154 | if (!upayload) { | |
155 | kleave(" = -ENOMEM"); | |
156 | return -ENOMEM; | |
157 | } | |
158 | ||
159 | upayload->datalen = result_len; | |
160 | memcpy(upayload->data, data, result_len); | |
161 | upayload->data[result_len] = '\0'; | |
162 | rcu_assign_pointer(key->payload.data, upayload); | |
163 | ||
164 | kleave(" = 0"); | |
165 | return 0; | |
166 | } | |
167 | ||
168 | /* | |
169 | * The description is of the form "[<type>:]<domain_name>" | |
170 | * | |
171 | * The domain name may be a simple name or an absolute domain name (which | |
172 | * should end with a period). The domain name is case-independent. | |
173 | */ | |
174 | static int | |
175 | dns_resolver_match(const struct key *key, const void *description) | |
176 | { | |
177 | int slen, dlen, ret = 0; | |
178 | const char *src = key->description, *dsp = description; | |
179 | ||
180 | kenter("%s,%s", src, dsp); | |
181 | ||
182 | if (!src || !dsp) | |
183 | goto no_match; | |
184 | ||
185 | if (strcasecmp(src, dsp) == 0) | |
186 | goto matched; | |
187 | ||
188 | slen = strlen(src); | |
189 | dlen = strlen(dsp); | |
190 | if (slen <= 0 || dlen <= 0) | |
191 | goto no_match; | |
192 | if (src[slen - 1] == '.') | |
193 | slen--; | |
194 | if (dsp[dlen - 1] == '.') | |
195 | dlen--; | |
196 | if (slen != dlen || strncasecmp(src, dsp, slen) != 0) | |
197 | goto no_match; | |
198 | ||
199 | matched: | |
200 | ret = 1; | |
201 | no_match: | |
202 | kleave(" = %d", ret); | |
203 | return ret; | |
204 | } | |
205 | ||
4a2d7892 WL |
206 | /* |
207 | * Describe a DNS key | |
208 | */ | |
209 | static void dns_resolver_describe(const struct key *key, struct seq_file *m) | |
210 | { | |
211 | int err = key->type_data.x[0]; | |
212 | ||
213 | seq_puts(m, key->description); | |
78b7280c DH |
214 | if (key_is_instantiated(key)) { |
215 | if (err) | |
216 | seq_printf(m, ": %d", err); | |
217 | else | |
218 | seq_printf(m, ": %u", key->datalen); | |
219 | } | |
4a2d7892 WL |
220 | } |
221 | ||
1362fa07 DH |
222 | /* |
223 | * read the DNS data | |
224 | * - the key's semaphore is read-locked | |
225 | */ | |
226 | static long dns_resolver_read(const struct key *key, | |
227 | char __user *buffer, size_t buflen) | |
228 | { | |
229 | if (key->type_data.x[0]) | |
230 | return key->type_data.x[0]; | |
231 | ||
232 | return user_read(key, buffer, buflen); | |
233 | } | |
234 | ||
1a4240f4 WL |
235 | struct key_type key_type_dns_resolver = { |
236 | .name = "dns_resolver", | |
237 | .instantiate = dns_resolver_instantiate, | |
238 | .match = dns_resolver_match, | |
239 | .revoke = user_revoke, | |
240 | .destroy = user_destroy, | |
4a2d7892 | 241 | .describe = dns_resolver_describe, |
1362fa07 | 242 | .read = dns_resolver_read, |
1a4240f4 WL |
243 | }; |
244 | ||
245 | static int __init init_dns_resolver(void) | |
246 | { | |
247 | struct cred *cred; | |
248 | struct key *keyring; | |
249 | int ret; | |
250 | ||
1a4240f4 WL |
251 | /* create an override credential set with a special thread keyring in |
252 | * which DNS requests are cached | |
253 | * | |
254 | * this is used to prevent malicious redirections from being installed | |
255 | * with add_key(). | |
256 | */ | |
257 | cred = prepare_kernel_cred(NULL); | |
258 | if (!cred) | |
259 | return -ENOMEM; | |
260 | ||
2a74dbb9 LT |
261 | keyring = keyring_alloc(".dns_resolver", |
262 | GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, | |
f8aa23a5 DH |
263 | (KEY_POS_ALL & ~KEY_POS_SETATTR) | |
264 | KEY_USR_VIEW | KEY_USR_READ, | |
265 | KEY_ALLOC_NOT_IN_QUOTA, NULL); | |
1a4240f4 WL |
266 | if (IS_ERR(keyring)) { |
267 | ret = PTR_ERR(keyring); | |
268 | goto failed_put_cred; | |
269 | } | |
270 | ||
1a4240f4 WL |
271 | ret = register_key_type(&key_type_dns_resolver); |
272 | if (ret < 0) | |
273 | goto failed_put_key; | |
274 | ||
275 | /* instruct request_key() to use this special keyring as a cache for | |
276 | * the results it looks up */ | |
700920eb | 277 | set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags); |
1a4240f4 WL |
278 | cred->thread_keyring = keyring; |
279 | cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; | |
280 | dns_resolver_cache = cred; | |
281 | ||
282 | kdebug("DNS resolver keyring: %d\n", key_serial(keyring)); | |
283 | return 0; | |
284 | ||
285 | failed_put_key: | |
286 | key_put(keyring); | |
287 | failed_put_cred: | |
288 | put_cred(cred); | |
289 | return ret; | |
290 | } | |
291 | ||
292 | static void __exit exit_dns_resolver(void) | |
293 | { | |
294 | key_revoke(dns_resolver_cache->thread_keyring); | |
295 | unregister_key_type(&key_type_dns_resolver); | |
296 | put_cred(dns_resolver_cache); | |
1a4240f4 WL |
297 | } |
298 | ||
299 | module_init(init_dns_resolver) | |
300 | module_exit(exit_dns_resolver) | |
301 | MODULE_LICENSE("GPL"); | |
f8aa23a5 | 302 |