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, 0644); 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 int opt_len, opt_nlen; 90 const char *eq; 91 char optval[128]; 92 93 next_opt = memchr(opt, '#', end - opt) ?: end; 94 opt_len = next_opt - opt; 95 if (opt_len <= 0 || opt_len > sizeof(optval)) { 96 pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n", 97 opt_len); 98 return -EINVAL; 99 } 100 101 eq = memchr(opt, '=', opt_len); 102 if (eq) { 103 opt_nlen = eq - opt; 104 eq++; 105 memcpy(optval, eq, next_opt - eq); 106 optval[next_opt - eq] = '\0'; 107 } else { 108 opt_nlen = opt_len; 109 optval[0] = '\0'; 110 } 111 112 kdebug("option '%*.*s' val '%s'", 113 opt_nlen, opt_nlen, opt, optval); 114 115 /* see if it's an error number representing a DNS error 116 * that's to be recorded as the result in this key */ 117 if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 && 118 memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) { 119 kdebug("dns error number option"); 120 121 ret = kstrtoul(optval, 10, &derrno); 122 if (ret < 0) 123 goto bad_option_value; 124 125 if (derrno < 1 || derrno > 511) 126 goto bad_option_value; 127 128 kdebug("dns error no. = %lu", derrno); 129 prep->payload.data[dns_key_error] = ERR_PTR(-derrno); 130 continue; 131 } 132 133 bad_option_value: 134 pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n", 135 opt_nlen, opt_nlen, opt); 136 return -EINVAL; 137 } while (opt = next_opt + 1, opt < end); 138 } 139 140 /* don't cache the result if we're caching an error saying there's no 141 * result */ 142 if (prep->payload.data[dns_key_error]) { 143 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error])); 144 return 0; 145 } 146 147 kdebug("store result"); 148 prep->quotalen = result_len; 149 150 upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL); 151 if (!upayload) { 152 kleave(" = -ENOMEM"); 153 return -ENOMEM; 154 } 155 156 upayload->datalen = result_len; 157 memcpy(upayload->data, data, result_len); 158 upayload->data[result_len] = '\0'; 159 160 prep->payload.data[dns_key_data] = upayload; 161 kleave(" = 0"); 162 return 0; 163 } 164 165 /* 166 * Clean up the preparse data 167 */ 168 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep) 169 { 170 pr_devel("==>%s()\n", __func__); 171 172 kfree(prep->payload.data[dns_key_data]); 173 } 174 175 /* 176 * The description is of the form "[<type>:]<domain_name>" 177 * 178 * The domain name may be a simple name or an absolute domain name (which 179 * should end with a period). The domain name is case-independent. 180 */ 181 static bool dns_resolver_cmp(const struct key *key, 182 const struct key_match_data *match_data) 183 { 184 int slen, dlen, ret = 0; 185 const char *src = key->description, *dsp = match_data->raw_data; 186 187 kenter("%s,%s", src, dsp); 188 189 if (!src || !dsp) 190 goto no_match; 191 192 if (strcasecmp(src, dsp) == 0) 193 goto matched; 194 195 slen = strlen(src); 196 dlen = strlen(dsp); 197 if (slen <= 0 || dlen <= 0) 198 goto no_match; 199 if (src[slen - 1] == '.') 200 slen--; 201 if (dsp[dlen - 1] == '.') 202 dlen--; 203 if (slen != dlen || strncasecmp(src, dsp, slen) != 0) 204 goto no_match; 205 206 matched: 207 ret = 1; 208 no_match: 209 kleave(" = %d", ret); 210 return ret; 211 } 212 213 /* 214 * Preparse the match criterion. 215 */ 216 static int dns_resolver_match_preparse(struct key_match_data *match_data) 217 { 218 match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE; 219 match_data->cmp = dns_resolver_cmp; 220 return 0; 221 } 222 223 /* 224 * Describe a DNS key 225 */ 226 static void dns_resolver_describe(const struct key *key, struct seq_file *m) 227 { 228 seq_puts(m, key->description); 229 if (key_is_positive(key)) { 230 int err = PTR_ERR(key->payload.data[dns_key_error]); 231 232 if (err) 233 seq_printf(m, ": %d", err); 234 else 235 seq_printf(m, ": %u", key->datalen); 236 } 237 } 238 239 /* 240 * read the DNS data 241 * - the key's semaphore is read-locked 242 */ 243 static long dns_resolver_read(const struct key *key, 244 char __user *buffer, size_t buflen) 245 { 246 int err = PTR_ERR(key->payload.data[dns_key_error]); 247 248 if (err) 249 return err; 250 251 return user_read(key, buffer, buflen); 252 } 253 254 struct key_type key_type_dns_resolver = { 255 .name = "dns_resolver", 256 .preparse = dns_resolver_preparse, 257 .free_preparse = dns_resolver_free_preparse, 258 .instantiate = generic_key_instantiate, 259 .match_preparse = dns_resolver_match_preparse, 260 .revoke = user_revoke, 261 .destroy = user_destroy, 262 .describe = dns_resolver_describe, 263 .read = dns_resolver_read, 264 }; 265 266 static int __init init_dns_resolver(void) 267 { 268 struct cred *cred; 269 struct key *keyring; 270 int ret; 271 272 /* create an override credential set with a special thread keyring in 273 * which DNS requests are cached 274 * 275 * this is used to prevent malicious redirections from being installed 276 * with add_key(). 277 */ 278 cred = prepare_kernel_cred(NULL); 279 if (!cred) 280 return -ENOMEM; 281 282 keyring = keyring_alloc(".dns_resolver", 283 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, 284 (KEY_POS_ALL & ~KEY_POS_SETATTR) | 285 KEY_USR_VIEW | KEY_USR_READ, 286 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); 287 if (IS_ERR(keyring)) { 288 ret = PTR_ERR(keyring); 289 goto failed_put_cred; 290 } 291 292 ret = register_key_type(&key_type_dns_resolver); 293 if (ret < 0) 294 goto failed_put_key; 295 296 /* instruct request_key() to use this special keyring as a cache for 297 * the results it looks up */ 298 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags); 299 cred->thread_keyring = keyring; 300 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; 301 dns_resolver_cache = cred; 302 303 kdebug("DNS resolver keyring: %d\n", key_serial(keyring)); 304 return 0; 305 306 failed_put_key: 307 key_put(keyring); 308 failed_put_cred: 309 put_cred(cred); 310 return ret; 311 } 312 313 static void __exit exit_dns_resolver(void) 314 { 315 key_revoke(dns_resolver_cache->thread_keyring); 316 unregister_key_type(&key_type_dns_resolver); 317 put_cred(dns_resolver_cache); 318 } 319 320 module_init(init_dns_resolver) 321 module_exit(exit_dns_resolver) 322 MODULE_LICENSE("GPL"); 323