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, write to the Free Software
  23  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  24  */
  25 #include <linux/module.h>
  26 #include <linux/moduleparam.h>
  27 #include <linux/slab.h>
  28 #include <linux/string.h>
  29 #include <linux/kernel.h>
  30 #include <linux/keyctl.h>
  31 #include <linux/err.h>
  32 #include <linux/seq_file.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, S_IWUSR | S_IRUGO);
  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  * Instantiate a user defined key for dns_resolver.
  51  *
  52  * The data must be a NUL-terminated string, with the NUL char accounted in
  53  * 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 static int
  62 dns_resolver_instantiate(struct key *key, struct key_preparsed_payload *prep)
  63 {
  64         struct user_key_payload *upayload;
  65         unsigned long derrno;
  66         int ret;
  67         size_t datalen = prep->datalen, result_len = 0;
  68         const char *data = prep->data, *end, *opt;
  69
  70         kenter("%%%d,%s,'%*.*s',%zu",
  71                key->serial, key->description,
  72                (int)datalen, (int)datalen, data, datalen);
  73
  74         if (datalen <= 1 || !data || data[datalen - 1] != '\0')
  75                 return -EINVAL;
  76         datalen--;
  77
  78         /* deal with any options embedded in the data */
  79         end = data + datalen;
  80         opt = memchr(data, '#', datalen);
  81         if (!opt) {
  82                 /* no options: the entire data is the result */
  83                 kdebug("no options");
  84                 result_len = datalen;
  85         } else {
  86                 const char *next_opt;
  87
  88                 result_len = opt - data;
  89                 opt++;
  90                 kdebug("options: '%s'", opt);
  91                 do {
  92                         const char *eq;
  93                         int opt_len, opt_nlen, opt_vlen, tmp;
  94
  95                         next_opt = memchr(opt, '#', end - opt) ?: end;
  96                         opt_len = next_opt - opt;
  97                         if (!opt_len) {
  98                                 printk(KERN_WARNING
  99                                        "Empty option to dns_resolver key %d\n",
 100                                        key->serial);
 101                                 return -EINVAL;
 102                         }
 103
 104                         eq = memchr(opt, '=', opt_len) ?: end;
 105                         opt_nlen = eq - opt;
 106                         eq++;
 107                         opt_vlen = next_opt - eq; /* will be -1 if no value */
 108
 109                         tmp = opt_vlen >= 0 ? opt_vlen : 0;
 110                         kdebug("option '%*.*s' val '%*.*s'",
 111                                opt_nlen, opt_nlen, opt, tmp, tmp, eq);
 112
 113                         /* see if it's an error number representing a DNS error
 114                          * that's to be recorded as the result in this key */
 115                         if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
 116                             memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
 117                                 kdebug("dns error number option");
 118                                 if (opt_vlen <= 0)
 119                                         goto bad_option_value;
 120
 121                                 ret = kstrtoul(eq, 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                                 key->type_data.x[0] = -derrno;
 130                                 continue;
 131                         }
 132
 133                 bad_option_value:
 134                         printk(KERN_WARNING
 135                                "Option '%*.*s' to dns_resolver key %d:"
 136                                " bad/missing value\n",
 137                                opt_nlen, opt_nlen, opt, key->serial);
 138                         return -EINVAL;
 139                 } while (opt = next_opt + 1, opt < end);
 140         }
 141
 142         /* don't cache the result if we're caching an error saying there's no
 143          * result */
 144         if (key->type_data.x[0]) {
 145                 kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
 146                 return 0;
 147         }
 148
 149         kdebug("store result");
 150         ret = key_payload_reserve(key, result_len);
 151         if (ret < 0)
 152                 return -EINVAL;
 153
 154         upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
 155         if (!upayload) {
 156                 kleave(" = -ENOMEM");
 157                 return -ENOMEM;
 158         }
 159
 160         upayload->datalen = result_len;
 161         memcpy(upayload->data, data, result_len);
 162         upayload->data[result_len] = '\0';
 163         rcu_assign_pointer(key->payload.data, upayload);
 164
 165         kleave(" = 0");
 166         return 0;
 167 }
 168
 169 /*
 170  * The description is of the form "[<type>:]<domain_name>"
 171  *
 172  * The domain name may be a simple name or an absolute domain name (which
 173  * should end with a period).  The domain name is case-independent.
 174  */
 175 static int
 176 dns_resolver_match(const struct key *key, const void *description)
 177 {
 178         int slen, dlen, ret = 0;
 179         const char *src = key->description, *dsp = description;
 180
 181         kenter("%s,%s", src, dsp);
 182
 183         if (!src || !dsp)
 184                 goto no_match;
 185
 186         if (strcasecmp(src, dsp) == 0)
 187                 goto matched;
 188
 189         slen = strlen(src);
 190         dlen = strlen(dsp);
 191         if (slen <= 0 || dlen <= 0)
 192                 goto no_match;
 193         if (src[slen - 1] == '.')
 194                 slen--;
 195         if (dsp[dlen - 1] == '.')
 196                 dlen--;
 197         if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
 198                 goto no_match;
 199
 200 matched:
 201         ret = 1;
 202 no_match:
 203         kleave(" = %d", ret);
 204         return ret;
 205 }
 206
 207 /*
 208  * Describe a DNS key
 209  */
 210 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 211 {
 212         int err = key->type_data.x[0];
 213
 214         seq_puts(m, key->description);
 215         if (key_is_instantiated(key)) {
 216                 if (err)
 217                         seq_printf(m, ": %d", err);
 218                 else
 219                         seq_printf(m, ": %u", key->datalen);
 220         }
 221 }
 222
 223 /*
 224  * read the DNS data
 225  * - the key's semaphore is read-locked
 226  */
 227 static long dns_resolver_read(const struct key *key,
 228                               char __user *buffer, size_t buflen)
 229 {
 230         if (key->type_data.x[0])
 231                 return key->type_data.x[0];
 232
 233         return user_read(key, buffer, buflen);
 234 }
 235
 236 struct key_type key_type_dns_resolver = {
 237         .name           = "dns_resolver",
 238         .instantiate    = dns_resolver_instantiate,
 239         .match          = dns_resolver_match,
 240         .revoke         = user_revoke,
 241         .destroy        = user_destroy,
 242         .describe       = dns_resolver_describe,
 243         .read           = dns_resolver_read,
 244 };
 245
 246 static int __init init_dns_resolver(void)
 247 {
 248         struct cred *cred;
 249         struct key *keyring;
 250         int ret;
 251
 252         /* create an override credential set with a special thread keyring in
 253          * which DNS requests are cached
 254          *
 255          * this is used to prevent malicious redirections from being installed
 256          * with add_key().
 257          */
 258         cred = prepare_kernel_cred(NULL);
 259         if (!cred)
 260                 return -ENOMEM;
 261
 262         keyring = keyring_alloc(".dns_resolver",
 263                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
 264                                 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 265                                 KEY_USR_VIEW | KEY_USR_READ,
 266                                 KEY_ALLOC_NOT_IN_QUOTA, NULL);
 267         if (IS_ERR(keyring)) {
 268                 ret = PTR_ERR(keyring);
 269                 goto failed_put_cred;
 270         }
 271
 272         ret = register_key_type(&key_type_dns_resolver);
 273         if (ret < 0)
 274                 goto failed_put_key;
 275
 276         /* instruct request_key() to use this special keyring as a cache for
 277          * the results it looks up */
 278         set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
 279         cred->thread_keyring = keyring;
 280         cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 281         dns_resolver_cache = cred;
 282
 283         kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 284         return 0;
 285
 286 failed_put_key:
 287         key_put(keyring);
 288 failed_put_cred:
 289         put_cred(cred);
 290         return ret;
 291 }
 292
 293 static void __exit exit_dns_resolver(void)
 294 {
 295         key_revoke(dns_resolver_cache->thread_keyring);
 296         unregister_key_type(&key_type_dns_resolver);
 297         put_cred(dns_resolver_cache);
 298 }
 299
 300 module_init(init_dns_resolver)
 301 module_exit(exit_dns_resolver)
 302 MODULE_LICENSE("GPL");
 303