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/ratelimit.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  * Preparse instantiation data for a dns_resolver key.
  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_preparse(struct key_preparsed_payload *prep)
  63 {
  64         struct user_key_payload *upayload;
  65         unsigned long derrno;
  66         int ret;
  67         int datalen = prep->datalen, result_len = 0;
  68         const char *data = prep->data, *end, *opt;
  69
  70         kenter("'%*.*s',%u", datalen, datalen, data, datalen);
  71
  72         if (datalen <= 1 || !data || data[datalen - 1] != '\0')
  73                 return -EINVAL;
  74         datalen--;
  75
  76         /* deal with any options embedded in the data */
  77         end = data + datalen;
  78         opt = memchr(data, '#', datalen);
  79         if (!opt) {
  80                 /* no options: the entire data is the result */
  81                 kdebug("no options");
  82                 result_len = datalen;
  83         } else {
  84                 const char *next_opt;
  85
  86                 result_len = opt - data;
  87                 opt++;
  88                 kdebug("options: '%s'", opt);
  89                 do {
  90                         int opt_len, opt_nlen;
  91                         const char *eq;
  92                         char optval[128];
  93
  94                         next_opt = memchr(opt, '#', end - opt) ?: end;
  95                         opt_len = next_opt - opt;
  96                         if (opt_len <= 0 || opt_len > sizeof(optval)) {
  97                                 pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
  98                                                     opt_len);
  99                                 return -EINVAL;
 100                         }
 101
 102                         eq = memchr(opt, '=', opt_len);
 103                         if (eq) {
 104                                 opt_nlen = eq - opt;
 105                                 eq++;
 106                                 memcpy(optval, eq, next_opt - eq);
 107                                 optval[next_opt - eq] = '\0';
 108                         } else {
 109                                 opt_nlen = opt_len;
 110                                 optval[0] = '\0';
 111                         }
 112
 113                         kdebug("option '%*.*s' val '%s'",
 114                                opt_nlen, opt_nlen, opt, optval);
 115
 116                         /* see if it's an error number representing a DNS error
 117                          * that's to be recorded as the result in this key */
 118                         if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
 119                             memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
 120                                 kdebug("dns error number option");
 121
 122                                 ret = kstrtoul(optval, 10, &derrno);
 123                                 if (ret < 0)
 124                                         goto bad_option_value;
 125
 126                                 if (derrno < 1 || derrno > 511)
 127                                         goto bad_option_value;
 128
 129                                 kdebug("dns error no. = %lu", derrno);
 130                                 prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
 131                                 continue;
 132                         }
 133
 134                 bad_option_value:
 135                         pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
 136                                             opt_nlen, opt_nlen, opt);
 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 (prep->payload.data[dns_key_error]) {
 144                 kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
 145                 return 0;
 146         }
 147
 148         kdebug("store result");
 149         prep->quotalen = result_len;
 150
 151         upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
 152         if (!upayload) {
 153                 kleave(" = -ENOMEM");
 154                 return -ENOMEM;
 155         }
 156
 157         upayload->datalen = result_len;
 158         memcpy(upayload->data, data, result_len);
 159         upayload->data[result_len] = '\0';
 160
 161         prep->payload.data[dns_key_data] = upayload;
 162         kleave(" = 0");
 163         return 0;
 164 }
 165
 166 /*
 167  * Clean up the preparse data
 168  */
 169 static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
 170 {
 171         pr_devel("==>%s()\n", __func__);
 172
 173         kfree(prep->payload.data[dns_key_data]);
 174 }
 175
 176 /*
 177  * The description is of the form "[<type>:]<domain_name>"
 178  *
 179  * The domain name may be a simple name or an absolute domain name (which
 180  * should end with a period).  The domain name is case-independent.
 181  */
 182 static bool dns_resolver_cmp(const struct key *key,
 183                              const struct key_match_data *match_data)
 184 {
 185         int slen, dlen, ret = 0;
 186         const char *src = key->description, *dsp = match_data->raw_data;
 187
 188         kenter("%s,%s", src, dsp);
 189
 190         if (!src || !dsp)
 191                 goto no_match;
 192
 193         if (strcasecmp(src, dsp) == 0)
 194                 goto matched;
 195
 196         slen = strlen(src);
 197         dlen = strlen(dsp);
 198         if (slen <= 0 || dlen <= 0)
 199                 goto no_match;
 200         if (src[slen - 1] == '.')
 201                 slen--;
 202         if (dsp[dlen - 1] == '.')
 203                 dlen--;
 204         if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
 205                 goto no_match;
 206
 207 matched:
 208         ret = 1;
 209 no_match:
 210         kleave(" = %d", ret);
 211         return ret;
 212 }
 213
 214 /*
 215  * Preparse the match criterion.
 216  */
 217 static int dns_resolver_match_preparse(struct key_match_data *match_data)
 218 {
 219         match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
 220         match_data->cmp = dns_resolver_cmp;
 221         return 0;
 222 }
 223
 224 /*
 225  * Describe a DNS key
 226  */
 227 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 228 {
 229         seq_puts(m, key->description);
 230         if (key_is_positive(key)) {
 231                 int err = PTR_ERR(key->payload.data[dns_key_error]);
 232
 233                 if (err)
 234                         seq_printf(m, ": %d", err);
 235                 else
 236                         seq_printf(m, ": %u", key->datalen);
 237         }
 238 }
 239
 240 /*
 241  * read the DNS data
 242  * - the key's semaphore is read-locked
 243  */
 244 static long dns_resolver_read(const struct key *key,
 245                               char __user *buffer, size_t buflen)
 246 {
 247         int err = PTR_ERR(key->payload.data[dns_key_error]);
 248
 249         if (err)
 250                 return err;
 251
 252         return user_read(key, buffer, buflen);
 253 }
 254
 255 struct key_type key_type_dns_resolver = {
 256         .name           = "dns_resolver",
 257         .preparse       = dns_resolver_preparse,
 258         .free_preparse  = dns_resolver_free_preparse,
 259         .instantiate    = generic_key_instantiate,
 260         .match_preparse = dns_resolver_match_preparse,
 261         .revoke         = user_revoke,
 262         .destroy        = user_destroy,
 263         .describe       = dns_resolver_describe,
 264         .read           = dns_resolver_read,
 265 };
 266
 267 static int __init init_dns_resolver(void)
 268 {
 269         struct cred *cred;
 270         struct key *keyring;
 271         int ret;
 272
 273         /* create an override credential set with a special thread keyring in
 274          * which DNS requests are cached
 275          *
 276          * this is used to prevent malicious redirections from being installed
 277          * with add_key().
 278          */
 279         cred = prepare_kernel_cred(NULL);
 280         if (!cred)
 281                 return -ENOMEM;
 282
 283         keyring = keyring_alloc(".dns_resolver",
 284                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
 285                                 (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 286                                 KEY_USR_VIEW | KEY_USR_READ,
 287                                 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 288         if (IS_ERR(keyring)) {
 289                 ret = PTR_ERR(keyring);
 290                 goto failed_put_cred;
 291         }
 292
 293         ret = register_key_type(&key_type_dns_resolver);
 294         if (ret < 0)
 295                 goto failed_put_key;
 296
 297         /* instruct request_key() to use this special keyring as a cache for
 298          * the results it looks up */
 299         set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
 300         cred->thread_keyring = keyring;
 301         cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 302         dns_resolver_cache = cred;
 303
 304         kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 305         return 0;
 306
 307 failed_put_key:
 308         key_put(keyring);
 309 failed_put_cred:
 310         put_cred(cred);
 311         return ret;
 312 }
 313
 314 static void __exit exit_dns_resolver(void)
 315 {
 316         key_revoke(dns_resolver_cache->thread_keyring);
 317         unregister_key_type(&key_type_dns_resolver);
 318         put_cred(dns_resolver_cache);
 319 }
 320
 321 module_init(init_dns_resolver)
 322 module_exit(exit_dns_resolver)
 323 MODULE_LICENSE("GPL");
 324