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, write to the Free Software 36 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 37 */ 38 39 #include <linux/module.h> 40 #include <linux/slab.h> 41 #include <linux/dns_resolver.h> 42 #include <linux/err.h> 43 #include <keys/dns_resolver-type.h> 44 #include <keys/user-type.h> 45 46 #include "internal.h" 47 48 /** 49 * dns_query - Query the DNS 50 * @type: Query type (or NULL for straight host->IP lookup) 51 * @name: Name to look up 52 * @namelen: Length of name 53 * @options: Request options (or NULL if no options) 54 * @_result: Where to place the returned data. 55 * @_expiry: Where to store the result expiry time (or NULL) 56 * 57 * The data will be returned in the pointer at *result, and the caller is 58 * responsible for freeing it. 59 * 60 * The description should be of the form "[<query_type>:]<domain_name>", and 61 * the options need to be appropriate for the query type requested. If no 62 * query_type is given, then the query is a straight hostname to IP address 63 * lookup. 64 * 65 * The DNS resolution lookup is performed by upcalling to userspace by way of 66 * requesting a key of type dns_resolver. 67 * 68 * Returns the size of the result on success, -ve error code otherwise. 69 */ 70 int dns_query(const char *type, const char *name, size_t namelen, 71 const char *options, char **_result, time_t *_expiry) 72 { 73 struct key *rkey; 74 struct user_key_payload *upayload; 75 const struct cred *saved_cred; 76 size_t typelen, desclen; 77 char *desc, *cp; 78 int ret, len; 79 80 kenter("%s,%*.*s,%zu,%s", 81 type, (int)namelen, (int)namelen, name, namelen, options); 82 83 if (!name || namelen == 0 || !_result) 84 return -EINVAL; 85 86 /* construct the query key description as "[<type>:]<name>" */ 87 typelen = 0; 88 desclen = 0; 89 if (type) { 90 typelen = strlen(type); 91 if (typelen < 1) 92 return -EINVAL; 93 desclen += typelen + 1; 94 } 95 96 if (!namelen) 97 namelen = strlen(name); 98 if (namelen < 3) 99 return -EINVAL; 100 desclen += namelen + 1; 101 102 desc = kmalloc(desclen, GFP_KERNEL); 103 if (!desc) 104 return -ENOMEM; 105 106 cp = desc; 107 if (type) { 108 memcpy(cp, type, typelen); 109 cp += typelen; 110 *cp++ = ':'; 111 } 112 memcpy(cp, name, namelen); 113 cp += namelen; 114 *cp = '\0'; 115 116 if (!options) 117 options = ""; 118 kdebug("call request_key(,%s,%s)", desc, options); 119 120 /* make the upcall, using special credentials to prevent the use of 121 * add_key() to preinstall malicious redirections 122 */ 123 saved_cred = override_creds(dns_resolver_cache); 124 rkey = request_key(&key_type_dns_resolver, desc, options); 125 revert_creds(saved_cred); 126 kfree(desc); 127 if (IS_ERR(rkey)) { 128 ret = PTR_ERR(rkey); 129 goto out; 130 } 131 132 down_read(&rkey->sem); 133 rkey->perm |= KEY_USR_VIEW; 134 135 ret = key_validate(rkey); 136 if (ret < 0) 137 goto put; 138 139 /* If the DNS server gave an error, return that to the caller */ 140 ret = rkey->type_data.x[0]; 141 if (ret) 142 goto put; 143 144 upayload = rcu_dereference_protected(rkey->payload.data, 145 lockdep_is_held(&rkey->sem)); 146 len = upayload->datalen; 147 148 ret = -ENOMEM; 149 *_result = kmalloc(len + 1, GFP_KERNEL); 150 if (!*_result) 151 goto put; 152 153 memcpy(*_result, upayload->data, len + 1); 154 if (_expiry) 155 *_expiry = rkey->expiry; 156 157 ret = len; 158 put: 159 up_read(&rkey->sem); 160 key_put(rkey); 161 out: 162 kleave(" = %d", ret); 163 return ret; 164 } 165 EXPORT_SYMBOL(dns_query); 166