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->payload.data[dns_key_error] = 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->payload.data[dns_key_error]) { 141 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error])); 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.data[dns_key_data] = 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.data[dns_key_data]); 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 seq_puts(m, key->description); 227 if (key_is_positive(key)) { 228 int err = PTR_ERR(key->payload.data[dns_key_error]); 229 230 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 int err = PTR_ERR(key->payload.data[dns_key_error]); 245 246 if (err) 247 return err; 248 249 return user_read(key, buffer, buflen); 250 } 251 252 struct key_type key_type_dns_resolver = { 253 .name = "dns_resolver", 254 .preparse = dns_resolver_preparse, 255 .free_preparse = dns_resolver_free_preparse, 256 .instantiate = generic_key_instantiate, 257 .match_preparse = dns_resolver_match_preparse, 258 .revoke = user_revoke, 259 .destroy = user_destroy, 260 .describe = dns_resolver_describe, 261 .read = dns_resolver_read, 262 }; 263 264 static int __init init_dns_resolver(void) 265 { 266 struct cred *cred; 267 struct key *keyring; 268 int ret; 269 270 /* create an override credential set with a special thread keyring in 271 * which DNS requests are cached 272 * 273 * this is used to prevent malicious redirections from being installed 274 * with add_key(). 275 */ 276 cred = prepare_kernel_cred(NULL); 277 if (!cred) 278 return -ENOMEM; 279 280 keyring = keyring_alloc(".dns_resolver", 281 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, 282 (KEY_POS_ALL & ~KEY_POS_SETATTR) | 283 KEY_USR_VIEW | KEY_USR_READ, 284 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); 285 if (IS_ERR(keyring)) { 286 ret = PTR_ERR(keyring); 287 goto failed_put_cred; 288 } 289 290 ret = register_key_type(&key_type_dns_resolver); 291 if (ret < 0) 292 goto failed_put_key; 293 294 /* instruct request_key() to use this special keyring as a cache for 295 * the results it looks up */ 296 set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags); 297 cred->thread_keyring = keyring; 298 cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; 299 dns_resolver_cache = cred; 300 301 kdebug("DNS resolver keyring: %d\n", key_serial(keyring)); 302 return 0; 303 304 failed_put_key: 305 key_put(keyring); 306 failed_put_cred: 307 put_cred(cred); 308 return ret; 309 } 310 311 static void __exit exit_dns_resolver(void) 312 { 313 key_revoke(dns_resolver_cache->thread_keyring); 314 unregister_key_type(&key_type_dns_resolver); 315 put_cred(dns_resolver_cache); 316 } 317 318 module_init(init_dns_resolver) 319 module_exit(exit_dns_resolver) 320 MODULE_LICENSE("GPL"); 321 322