LXR linux/net/dns_resolver/dns

   1/* Upcall routine, designed to work as a key type and working through
   2 * /sbin/request-key to contact userspace when handling DNS queries.
   3 *
   4 * See Documentation/networking/dns_resolver.txt
   5 *
   6 *   Copyright (c) 2007 Igor Mammedov
   7 *   Author(s): Igor Mammedov (niallain@gmail.com)
   8 *              Steve French (sfrench@us.ibm.com)
   9 *              Wang Lei (wang840925@gmail.com)
  10 *              David Howells (dhowells@redhat.com)
  11 *
  12 *   The upcall wrapper used to make an arbitrary DNS query.
  13 *
  14 *   This function requires the appropriate userspace tool dns.upcall to be
  15 *   installed and something like the following lines should be added to the
  16 *   /etc/request-key.conf file:
  17 *
  18 *      create dns_resolver * * /sbin/dns.upcall %k
  19 *
  20 *   For example to use this module to query AFSDB RR:
  21 *
  22 *      create dns_resolver afsdb:* * /sbin/dns.afsdb %k
  23 *
  24 *   This library is free software; you can redistribute it and/or modify
  25 *   it under the terms of the GNU Lesser General Public License as published
  26 *   by the Free Software Foundation; either version 2.1 of the License, or
  27 *   (at your option) any later version.
  28 *
  29 *   This library is distributed in the hope that it will be useful,
  30 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  31 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
  32 *   the GNU Lesser General Public License for more details.
  33 *
  34 *   You should have received a copy of the GNU Lesser General Public License
  35 *   along with this library; if not, see <http://www.gnu.org/licenses/>.
  36 */
  37
  38#include <linux/module.h>
  39#include <linux/slab.h>
  40#include <linux/cred.h>
  41#include <linux/dns_resolver.h>
  42#include <linux/err.h>
  43
  44#include <keys/dns_resolver-type.h>
  45#include <keys/user-type.h>
  46
  47#include "internal.h"
  48
  49/**
  50 * dns_query - Query the DNS
  51 * @type: Query type (or NULL for straight host->IP lookup)
  52 * @name: Name to look up
  53 * @namelen: Length of name
  54 * @options: Request options (or NULL if no options)
  55 * @_result: Where to place the returned data (or NULL)
  56 * @_expiry: Where to store the result expiry time (or NULL)
  57 *
  58 * The data will be returned in the pointer at *result, if provided, and the
  59 * caller is responsible for freeing it.
  60 *
  61 * The description should be of the form "[<query_type>:]<domain_name>", and
  62 * the options need to be appropriate for the query type requested.  If no
  63 * query_type is given, then the query is a straight hostname to IP address
  64 * lookup.
  65 *
  66 * The DNS resolution lookup is performed by upcalling to userspace by way of
  67 * requesting a key of type dns_resolver.
  68 *
  69 * Returns the size of the result on success, -ve error code otherwise.
  70 */
  71int dns_query(const char *type, const char *name, size_t namelen,
  72              const char *options, char **_result, time64_t *_expiry)
  73{
  74        struct key *rkey;
  75        struct user_key_payload *upayload;
  76        const struct cred *saved_cred;
  77        size_t typelen, desclen;
  78        char *desc, *cp;
  79        int ret, len;
  80
  81        kenter("%s,%*.*s,%zu,%s",
  82               type, (int)namelen, (int)namelen, name, namelen, options);
  83
  84        if (!name || namelen == 0)
  85                return -EINVAL;
  86
  87        /* construct the query key description as "[<type>:]<name>" */
  88        typelen = 0;
  89        desclen = 0;
  90        if (type) {
  91                typelen = strlen(type);
  92                if (typelen < 1)
  93                        return -EINVAL;
  94                desclen += typelen + 1;
  95        }
  96
  97        if (!namelen)
  98                namelen = strnlen(name, 256);
  99        if (namelen < 3 || namelen > 255)
 100                return -EINVAL;
 101        desclen += namelen + 1;
 102
 103        desc = kmalloc(desclen, GFP_KERNEL);
 104        if (!desc)
 105                return -ENOMEM;
 106
 107        cp = desc;
 108        if (type) {
 109                memcpy(cp, type, typelen);
 110                cp += typelen;
 111                *cp++ = ':';
 112        }
 113        memcpy(cp, name, namelen);
 114        cp += namelen;
 115        *cp = '\0';
 116
 117        if (!options)
 118                options = "";
 119        kdebug("call request_key(,%s,%s)", desc, options);
 120
 121        /* make the upcall, using special credentials to prevent the use of
 122         * add_key() to preinstall malicious redirections
 123         */
 124        saved_cred = override_creds(dns_resolver_cache);
 125        rkey = request_key(&key_type_dns_resolver, desc, options);
 126        revert_creds(saved_cred);
 127        kfree(desc);
 128        if (IS_ERR(rkey)) {
 129                ret = PTR_ERR(rkey);
 130                goto out;
 131        }
 132
 133        down_read(&rkey->sem);
 134        set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
 135        rkey->perm |= KEY_USR_VIEW;
 136
 137        ret = key_validate(rkey);
 138        if (ret < 0)
 139                goto put;
 140
 141        /* If the DNS server gave an error, return that to the caller */
 142        ret = PTR_ERR(rkey->payload.data[dns_key_error]);
 143        if (ret)
 144                goto put;
 145
 146        upayload = user_key_payload_locked(rkey);
 147        len = upayload->datalen;
 148
 149        if (_result) {
 150                ret = -ENOMEM;
 151                *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
 152                if (!*_result)
 153                        goto put;
 154        }
 155
 156        if (_expiry)
 157                *_expiry = rkey->expiry;
 158
 159        ret = len;
 160put:
 161        up_read(&rkey->sem);
 162        key_put(rkey);
 163out:
 164        kleave(" = %d", ret);
 165        return ret;
 166}
 167EXPORT_SYMBOL(dns_query);
 168