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