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 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, const void *_data, size_t datalen)
  63 {
  64         struct user_key_payload *upayload;
  65         unsigned long derrno;
  66         int ret;
  67         size_t result_len = 0;
  68         const char *data = _data, *end, *opt;
  69
  70         kenter("%%%d,%s,'%s',%zu",
  71                key->serial, key->description, data, datalen);
  72
  73         if (datalen <= 1 || !data || data[datalen - 1] != '\0')
  74                 return -EINVAL;
  75         datalen--;
  76
  77         /* deal with any options embedded in the data */
  78         end = data + datalen;
  79         opt = memchr(data, '#', datalen);
  80         if (!opt) {
  81                 /* no options: the entire data is the result */
  82                 kdebug("no options");
  83                 result_len = datalen;
  84         } else {
  85                 const char *next_opt;
  86
  87                 result_len = opt - data;
  88                 opt++;
  89                 kdebug("options: '%s'", opt);
  90                 do {
  91                         const char *eq;
  92                         int opt_len, opt_nlen, opt_vlen, tmp;
  93
  94                         next_opt = memchr(opt, '#', end - opt) ?: end;
  95                         opt_len = next_opt - opt;
  96                         if (!opt_len) {
  97                                 printk(KERN_WARNING
  98                                        "Empty option to dns_resolver key %d\n",
  99                                        key->serial);
 100                                 return -EINVAL;
 101                         }
 102
 103                         eq = memchr(opt, '=', opt_len) ?: end;
 104                         opt_nlen = eq - opt;
 105                         eq++;
 106                         opt_vlen = next_opt - eq; /* will be -1 if no value */
 107
 108                         tmp = opt_vlen >= 0 ? opt_vlen : 0;
 109                         kdebug("option '%*.*s' val '%*.*s'",
 110                                opt_nlen, opt_nlen, opt, tmp, tmp, eq);
 111
 112                         /* see if it's an error number representing a DNS error
 113                          * that's to be recorded as the result in this key */
 114                         if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
 115                             memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
 116                                 kdebug("dns error number option");
 117                                 if (opt_vlen <= 0)
 118                                         goto bad_option_value;
 119
 120                                 ret = strict_strtoul(eq, 10, &derrno);
 121                                 if (ret < 0)
 122                                         goto bad_option_value;
 123
 124                                 if (derrno < 1 || derrno > 511)
 125                                         goto bad_option_value;
 126
 127                                 kdebug("dns error no. = %lu", derrno);
 128                                 key->type_data.x[0] = -derrno;
 129                                 continue;
 130                         }
 131
 132                 bad_option_value:
 133                         printk(KERN_WARNING
 134                                "Option '%*.*s' to dns_resolver key %d:"
 135                                " bad/missing value\n",
 136                                opt_nlen, opt_nlen, opt, key->serial);
 137                         return -EINVAL;
 138                 } while (opt = next_opt + 1, opt < end);
 139         }
 140
 141         /* don't cache the result if we're caching an error saying there's no
 142          * result */
 143         if (key->type_data.x[0]) {
 144                 kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
 145                 return 0;
 146         }
 147
 148         kdebug("store result");
 149         ret = key_payload_reserve(key, result_len);
 150         if (ret < 0)
 151                 return -EINVAL;
 152
 153         upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
 154         if (!upayload) {
 155                 kleave(" = -ENOMEM");
 156                 return -ENOMEM;
 157         }
 158
 159         upayload->datalen = result_len;
 160         memcpy(upayload->data, data, result_len);
 161         upayload->data[result_len] = '\0';
 162         rcu_assign_pointer(key->payload.data, upayload);
 163
 164         kleave(" = 0");
 165         return 0;
 166 }
 167
 168 /*
 169  * The description is of the form "[<type>:]<domain_name>"
 170  *
 171  * The domain name may be a simple name or an absolute domain name (which
 172  * should end with a period).  The domain name is case-independent.
 173  */
 174 static int
 175 dns_resolver_match(const struct key *key, const void *description)
 176 {
 177         int slen, dlen, ret = 0;
 178         const char *src = key->description, *dsp = description;
 179
 180         kenter("%s,%s", src, dsp);
 181
 182         if (!src || !dsp)
 183                 goto no_match;
 184
 185         if (strcasecmp(src, dsp) == 0)
 186                 goto matched;
 187
 188         slen = strlen(src);
 189         dlen = strlen(dsp);
 190         if (slen <= 0 || dlen <= 0)
 191                 goto no_match;
 192         if (src[slen - 1] == '.')
 193                 slen--;
 194         if (dsp[dlen - 1] == '.')
 195                 dlen--;
 196         if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
 197                 goto no_match;
 198
 199 matched:
 200         ret = 1;
 201 no_match:
 202         kleave(" = %d", ret);
 203         return ret;
 204 }
 205
 206 /*
 207  * Describe a DNS key
 208  */
 209 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 210 {
 211         int err = key->type_data.x[0];
 212
 213         seq_puts(m, key->description);
 214         if (err)
 215                 seq_printf(m, ": %d", err);
 216         else
 217                 seq_printf(m, ": %u", key->datalen);
 218 }
 219
 220 struct key_type key_type_dns_resolver = {
 221         .name           = "dns_resolver",
 222         .instantiate    = dns_resolver_instantiate,
 223         .match          = dns_resolver_match,
 224         .revoke         = user_revoke,
 225         .destroy        = user_destroy,
 226         .describe       = dns_resolver_describe,
 227         .read           = user_read,
 228 };
 229
 230 static int __init init_dns_resolver(void)
 231 {
 232         struct cred *cred;
 233         struct key *keyring;
 234         int ret;
 235
 236         printk(KERN_NOTICE "Registering the %s key type\n",
 237                key_type_dns_resolver.name);
 238
 239         /* create an override credential set with a special thread keyring in
 240          * which DNS requests are cached
 241          *
 242          * this is used to prevent malicious redirections from being installed
 243          * with add_key().
 244          */
 245         cred = prepare_kernel_cred(NULL);
 246         if (!cred)
 247                 return -ENOMEM;
 248
 249         keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
 250                             (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 251                             KEY_USR_VIEW | KEY_USR_READ,
 252                             KEY_ALLOC_NOT_IN_QUOTA);
 253         if (IS_ERR(keyring)) {
 254                 ret = PTR_ERR(keyring);
 255                 goto failed_put_cred;
 256         }
 257
 258         ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
 259         if (ret < 0)
 260                 goto failed_put_key;
 261
 262         ret = register_key_type(&key_type_dns_resolver);
 263         if (ret < 0)
 264                 goto failed_put_key;
 265
 266         /* instruct request_key() to use this special keyring as a cache for
 267          * the results it looks up */
 268         cred->thread_keyring = keyring;
 269         cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 270         dns_resolver_cache = cred;
 271
 272         kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 273         return 0;
 274
 275 failed_put_key:
 276         key_put(keyring);
 277 failed_put_cred:
 278         put_cred(cred);
 279         return ret;
 280 }
 281
 282 static void __exit exit_dns_resolver(void)
 283 {
 284         key_revoke(dns_resolver_cache->thread_keyring);
 285         unregister_key_type(&key_type_dns_resolver);
 286         put_cred(dns_resolver_cache);
 287         printk(KERN_NOTICE "Unregistered %s key type\n",
 288                key_type_dns_resolver.name);
 289 }
 290
 291 module_init(init_dns_resolver)
 292 module_exit(exit_dns_resolver)
 293 MODULE_LICENSE("GPL");