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  * Instantiate a user defined key for dns_resolver.
  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_instantiate(struct key *key, struct key_preparsed_payload *prep)
  62 {
  63         struct user_key_payload *upayload;
  64         unsigned long derrno;
  65         int ret;
  66         size_t datalen = prep->datalen, result_len = 0;
  67         const char *data = prep->data, *end, *opt;
  68
  69         kenter("%%%d,%s,'%*.*s',%zu",
  70                key->serial, key->description,
  71                (int)datalen, (int)datalen, 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 = kstrtoul(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 (key_is_instantiated(key)) {
 215                 if (err)
 216                         seq_printf(m, ": %d", err);
 217                 else
 218                         seq_printf(m, ": %u", key->datalen);
 219         }
 220 }
 221
 222 /*
 223  * read the DNS data
 224  * - the key's semaphore is read-locked
 225  */
 226 static long dns_resolver_read(const struct key *key,
 227                               char __user *buffer, size_t buflen)
 228 {
 229         if (key->type_data.x[0])
 230                 return key->type_data.x[0];
 231
 232         return user_read(key, buffer, buflen);
 233 }
 234
 235 struct key_type key_type_dns_resolver = {
 236         .name           = "dns_resolver",
 237         .instantiate    = dns_resolver_instantiate,
 238         .match          = dns_resolver_match,
 239         .revoke         = user_revoke,
 240         .destroy        = user_destroy,
 241         .describe       = dns_resolver_describe,
 242         .read           = dns_resolver_read,
 243 };
 244
 245 static int __init init_dns_resolver(void)
 246 {
 247         struct cred *cred;
 248         struct key *keyring;
 249         int ret;
 250
 251         /* create an override credential set with a special thread keyring in
 252          * which DNS requests are cached
 253          *
 254          * this is used to prevent malicious redirections from being installed
 255          * with add_key().
 256          */
 257         cred = prepare_kernel_cred(NULL);
 258         if (!cred)
 259                 return -ENOMEM;
 260
 261         keyring = keyring_alloc(".dns_resolver",
 262                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
 263                                 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 264                                 KEY_USR_VIEW | KEY_USR_READ,
 265                                 KEY_ALLOC_NOT_IN_QUOTA, NULL);
 266         if (IS_ERR(keyring)) {
 267                 ret = PTR_ERR(keyring);
 268                 goto failed_put_cred;
 269         }
 270
 271         ret = register_key_type(&key_type_dns_resolver);
 272         if (ret < 0)
 273                 goto failed_put_key;
 274
 275         /* instruct request_key() to use this special keyring as a cache for
 276          * the results it looks up */
 277         set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
 278         cred->thread_keyring = keyring;
 279         cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 280         dns_resolver_cache = cred;
 281
 282         kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 283         return 0;
 284
 285 failed_put_key:
 286         key_put(keyring);
 287 failed_put_cred:
 288         put_cred(cred);
 289         return ret;
 290 }
 291
 292 static void __exit exit_dns_resolver(void)
 293 {
 294         key_revoke(dns_resolver_cache->thread_keyring);
 295         unregister_key_type(&key_type_dns_resolver);
 296         put_cred(dns_resolver_cache);
 297 }
 298
 299 module_init(init_dns_resolver)
 300 module_exit(exit_dns_resolver)
 301 MODULE_LICENSE("GPL");
 302