xref: /linux/net/dns_resolver/dns_key.c (revision ca55b2fef3a9373fcfc30f82fd26bc7fccbda732) 
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/kernel.h>
29 #include <linux/keyctl.h>
30 #include <linux/err.h>
31 #include <linux/seq_file.h>
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 
40 unsigned int dns_resolver_debug;
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 
46 #define	DNS_ERRORNO_OPTION	"dnserror"
47 
48 /*
49  * Preparse instantiation data for a dns_resolver key.
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
61 dns_resolver_preparse(struct key_preparsed_payload *prep)
62 {
63 	struct user_key_payload *upayload;
64 	unsigned long derrno;
65 	int ret;
66 	int datalen = prep->datalen, result_len = 0;
67 	const char *data = prep->data, *end, *opt;
68 
69 	kenter("'%*.*s',%u", datalen, datalen, data, datalen);
70 
71 	if (datalen <= 1 || !data || data[datalen - 1] != '\0')
72 		return -EINVAL;
73 	datalen--;
74 
75 	/* deal with any options embedded in the data */
76 	end = data + datalen;
77 	opt = memchr(data, '#', datalen);
78 	if (!opt) {
79 		/* no options: the entire data is the result */
80 		kdebug("no options");
81 		result_len = datalen;
82 	} else {
83 		const char *next_opt;
84 
85 		result_len = opt - data;
86 		opt++;
87 		kdebug("options: '%s'", opt);
88 		do {
89 			const char *eq;
90 			int opt_len, opt_nlen, opt_vlen, tmp;
91 
92 			next_opt = memchr(opt, '#', end - opt) ?: end;
93 			opt_len = next_opt - opt;
94 			if (!opt_len) {
95 				printk(KERN_WARNING
96 				       "Empty option to dns_resolver key\n");
97 				return -EINVAL;
98 			}
99 
100 			eq = memchr(opt, '=', opt_len) ?: end;
101 			opt_nlen = eq - opt;
102 			eq++;
103 			opt_vlen = next_opt - eq; /* will be -1 if no value */
104 
105 			tmp = opt_vlen >= 0 ? opt_vlen : 0;
106 			kdebug("option '%*.*s' val '%*.*s'",
107 			       opt_nlen, opt_nlen, opt, tmp, tmp, eq);
108 
109 			/* see if it's an error number representing a DNS error
110 			 * that's to be recorded as the result in this key */
111 			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
112 			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
113 				kdebug("dns error number option");
114 				if (opt_vlen <= 0)
115 					goto bad_option_value;
116 
117 				ret = kstrtoul(eq, 10, &derrno);
118 				if (ret < 0)
119 					goto bad_option_value;
120 
121 				if (derrno < 1 || derrno > 511)
122 					goto bad_option_value;
123 
124 				kdebug("dns error no. = %lu", derrno);
125 				prep->type_data[0] = ERR_PTR(-derrno);
126 				continue;
127 			}
128 
129 		bad_option_value:
130 			printk(KERN_WARNING
131 			       "Option '%*.*s' to dns_resolver key:"
132 			       " bad/missing value\n",
133 			       opt_nlen, opt_nlen, opt);
134 			return -EINVAL;
135 		} while (opt = next_opt + 1, opt < end);
136 	}
137 
138 	/* don't cache the result if we're caching an error saying there's no
139 	 * result */
140 	if (prep->type_data[0]) {
141 		kleave(" = 0 [h_error %ld]", PTR_ERR(prep->type_data[0]));
142 		return 0;
143 	}
144 
145 	kdebug("store result");
146 	prep->quotalen = result_len;
147 
148 	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
149 	if (!upayload) {
150 		kleave(" = -ENOMEM");
151 		return -ENOMEM;
152 	}
153 
154 	upayload->datalen = result_len;
155 	memcpy(upayload->data, data, result_len);
156 	upayload->data[result_len] = '\0';
157 
158 	prep->payload[0] = upayload;
159 	kleave(" = 0");
160 	return 0;
161 }
162 
163 /*
164  * Clean up the preparse data
165  */
166 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
167 {
168 	pr_devel("==>%s()\n", __func__);
169 
170 	kfree(prep->payload[0]);
171 }
172 
173 /*
174  * The description is of the form "[<type>:]<domain_name>"
175  *
176  * The domain name may be a simple name or an absolute domain name (which
177  * should end with a period).  The domain name is case-independent.
178  */
179 static bool dns_resolver_cmp(const struct key *key,
180 			     const struct key_match_data *match_data)
181 {
182 	int slen, dlen, ret = 0;
183 	const char *src = key->description, *dsp = match_data->raw_data;
184 
185 	kenter("%s,%s", src, dsp);
186 
187 	if (!src || !dsp)
188 		goto no_match;
189 
190 	if (strcasecmp(src, dsp) == 0)
191 		goto matched;
192 
193 	slen = strlen(src);
194 	dlen = strlen(dsp);
195 	if (slen <= 0 || dlen <= 0)
196 		goto no_match;
197 	if (src[slen - 1] == '.')
198 		slen--;
199 	if (dsp[dlen - 1] == '.')
200 		dlen--;
201 	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
202 		goto no_match;
203 
204 matched:
205 	ret = 1;
206 no_match:
207 	kleave(" = %d", ret);
208 	return ret;
209 }
210 
211 /*
212  * Preparse the match criterion.
213  */
214 static int dns_resolver_match_preparse(struct key_match_data *match_data)
215 {
216 	match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
217 	match_data->cmp = dns_resolver_cmp;
218 	return 0;
219 }
220 
221 /*
222  * Describe a DNS key
223  */
224 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
225 {
226 	int err = key->type_data.x[0];
227 
228 	seq_puts(m, key->description);
229 	if (key_is_instantiated(key)) {
230 		if (err)
231 			seq_printf(m, ": %d", err);
232 		else
233 			seq_printf(m, ": %u", key->datalen);
234 	}
235 }
236 
237 /*
238  * read the DNS data
239  * - the key's semaphore is read-locked
240  */
241 static long dns_resolver_read(const struct key *key,
242 			      char __user *buffer, size_t buflen)
243 {
244 	if (key->type_data.x[0])
245 		return key->type_data.x[0];
246 
247 	return user_read(key, buffer, buflen);
248 }
249 
250 struct key_type key_type_dns_resolver = {
251 	.name		= "dns_resolver",
252 	.preparse	= dns_resolver_preparse,
253 	.free_preparse	= dns_resolver_free_preparse,
254 	.instantiate	= generic_key_instantiate,
255 	.match_preparse	= dns_resolver_match_preparse,
256 	.revoke		= user_revoke,
257 	.destroy	= user_destroy,
258 	.describe	= dns_resolver_describe,
259 	.read		= dns_resolver_read,
260 };
261 
262 static int __init init_dns_resolver(void)
263 {
264 	struct cred *cred;
265 	struct key *keyring;
266 	int ret;
267 
268 	/* create an override credential set with a special thread keyring in
269 	 * which DNS requests are cached
270 	 *
271 	 * this is used to prevent malicious redirections from being installed
272 	 * with add_key().
273 	 */
274 	cred = prepare_kernel_cred(NULL);
275 	if (!cred)
276 		return -ENOMEM;
277 
278 	keyring = keyring_alloc(".dns_resolver",
279 				GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
280 				(KEY_POS_ALL & ~KEY_POS_SETATTR) |
281 				KEY_USR_VIEW | KEY_USR_READ,
282 				KEY_ALLOC_NOT_IN_QUOTA, NULL);
283 	if (IS_ERR(keyring)) {
284 		ret = PTR_ERR(keyring);
285 		goto failed_put_cred;
286 	}
287 
288 	ret = register_key_type(&key_type_dns_resolver);
289 	if (ret < 0)
290 		goto failed_put_key;
291 
292 	/* instruct request_key() to use this special keyring as a cache for
293 	 * the results it looks up */
294 	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
295 	cred->thread_keyring = keyring;
296 	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
297 	dns_resolver_cache = cred;
298 
299 	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
300 	return 0;
301 
302 failed_put_key:
303 	key_put(keyring);
304 failed_put_cred:
305 	put_cred(cred);
306 	return ret;
307 }
308 
309 static void __exit exit_dns_resolver(void)
310 {
311 	key_revoke(dns_resolver_cache->thread_keyring);
312 	unregister_key_type(&key_type_dns_resolver);
313 	put_cred(dns_resolver_cache);
314 }
315 
316 module_init(init_dns_resolver)
317 module_exit(exit_dns_resolver)
318 MODULE_LICENSE("GPL");
319 
320