linux/net/dns_resolver/dns_key.c
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   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
  37MODULE_DESCRIPTION("DNS Resolver");
  38MODULE_AUTHOR("Wang Lei");
  39MODULE_LICENSE("GPL");
  40
  41unsigned int dns_resolver_debug;
  42module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
  43MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
  44
  45const 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 */
  61static int
  62dns_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 = strict_strtoul(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 */
 175static int
 176dns_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
 200matched:
 201        ret = 1;
 202no_match:
 203        kleave(" = %d", ret);
 204        return ret;
 205}
 206
 207/*
 208 * Describe a DNS key
 209 */
 210static 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 */
 227static 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
 236struct 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
 246static 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 = key_alloc(&key_type_keyring, ".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);
 267        if (IS_ERR(keyring)) {
 268                ret = PTR_ERR(keyring);
 269                goto failed_put_cred;
 270        }
 271
 272        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
 273        if (ret < 0)
 274                goto failed_put_key;
 275
 276        ret = register_key_type(&key_type_dns_resolver);
 277        if (ret < 0)
 278                goto failed_put_key;
 279
 280        /* instruct request_key() to use this special keyring as a cache for
 281         * the results it looks up */
 282        set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
 283        cred->thread_keyring = keyring;
 284        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 285        dns_resolver_cache = cred;
 286
 287        kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
 288        return 0;
 289
 290failed_put_key:
 291        key_put(keyring);
 292failed_put_cred:
 293        put_cred(cred);
 294        return ret;
 295}
 296
 297static void __exit exit_dns_resolver(void)
 298{
 299        key_revoke(dns_resolver_cache->thread_keyring);
 300        unregister_key_type(&key_type_dns_resolver);
 301        put_cred(dns_resolver_cache);
 302}
 303
 304module_init(init_dns_resolver)
 305module_exit(exit_dns_resolver)
 306MODULE_LICENSE("GPL");
 307
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