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.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 *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");