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 */ 71 int 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; 160 put: 161 up_read(&rkey->sem); 162 key_put(rkey); 163 out: 164 kleave(" = %d", ret); 165 return ret; 166 } 167 EXPORT_SYMBOL(dns_query); 168