net/dns_resolver/dns_key.c

   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(data, '#', 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(opt, '#', 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(opt, '=', 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(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
 179                                 kdebug("dns error number option");
 180
 181                                 ret = kstrtoul(optval, 10, &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(-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(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(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(src, 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(src, dsp, 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, key->description);
 290         if (key_is_positive(key)) {
 291                 int err = PTR_ERR(key->payload.data[dns_key_error]);
 292
 293                 if (err)
 294                         seq_printf(m, ": %d", err);
 295                 else
 296                         seq_printf(m, ": %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(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(NULL);
 341         if (!cred)
 342                 return -ENOMEM;
 343
 344         keyring = keyring_alloc(".dns_resolver",
 345                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
 346                                 (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(dns_resolver_cache->thread_keyring);
 378         unregister_key_type(&key_type_dns_resolver);
 379         put_cred(dns_resolver_cache);
 380 }
 381
 382 module_init(init_dns_resolver)
 383 module_exit(exit_dns_resolver)
 384 MODULE_LICENSE("GPL");