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, 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->type_data[0] = 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->type_data[0]) {
 141                 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->type_data[0]));
 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[0] = 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[0]);
 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 int
 180 dns_resolver_match(const struct key *key, const void *description)
 181 {
 182         int slen, dlen, ret = 0;
 183         const char *src = key->description, *dsp = description;
 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  * Describe a DNS key
 213  */
 214 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 215 {
 216         int err = key->type_data.x[0];
 217
 218         seq_puts(m, key->description);
 219         if (key_is_instantiated(key)) {
 220                 if (err)
 221                         seq_printf(m, ": %d", err);
 222                 else
 223                         seq_printf(m, ": %u", key->datalen);
 224         }
 225 }
 226
 227 /*
 228  * read the DNS data
 229  * - the key's semaphore is read-locked
 230  */
 231 static long dns_resolver_read(const struct key *key,
 232                               char __user *buffer, size_t buflen)
 233 {
 234         if (key->type_data.x[0])
 235                 return key->type_data.x[0];
 236
 237         return user_read(key, buffer, buflen);
 238 }
 239
 240 struct key_type key_type_dns_resolver = {
 241         .name           = "dns_resolver",
 242         .preparse       = dns_resolver_preparse,
 243         .free_preparse  = dns_resolver_free_preparse,
 244         .instantiate    = generic_key_instantiate,
 245         .match          = dns_resolver_match,
 246         .revoke         = user_revoke,
 247         .destroy        = user_destroy,
 248         .describe       = dns_resolver_describe,
 249         .read           = dns_resolver_read,
 250 };
 251
 252 static int __init init_dns_resolver(void)
 253 {
 254         struct cred *cred;
 255         struct key *keyring;
 256         int ret;
 257
 258         /* create an override credential set with a special thread keyring in
 259          * which DNS requests are cached
 260          *
 261          * this is used to prevent malicious redirections from being installed
 262          * with add_key().
 263          */
 264         cred = prepare_kernel_cred(NULL);
 265         if (!cred)
 266                 return -ENOMEM;
 267
 268         keyring = keyring_alloc(".dns_resolver",
 269                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
 270                                 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 271                                 KEY_USR_VIEW | KEY_USR_READ,
 272                                 KEY_ALLOC_NOT_IN_QUOTA, NULL);
 273         if (IS_ERR(keyring)) {
 274                 ret = PTR_ERR(keyring);
 275                 goto failed_put_cred;
 276         }
 277
 278         ret = register_key_type(&key_type_dns_resolver);
 279         if (ret < 0)
 280                 goto failed_put_key;
 281
 282         /* instruct request_key() to use this special keyring as a cache for
 283          * the results it looks up */
 284         set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
 285         cred->thread_keyring = keyring;
 286         cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 287         dns_resolver_cache = cred;
 288
 289         kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 290         return 0;
 291
 292 failed_put_key:
 293         key_put(keyring);
 294 failed_put_cred:
 295         put_cred(cred);
 296         return ret;
 297 }
 298
 299 static void __exit exit_dns_resolver(void)
 300 {
 301         key_revoke(dns_resolver_cache->thread_keyring);
 302         unregister_key_type(&key_type_dns_resolver);
 303         put_cred(dns_resolver_cache);
 304 }
 305
 306 module_init(init_dns_resolver)
 307 module_exit(exit_dns_resolver)
 308 MODULE_LICENSE("GPL");
 309