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 #include <net/net_namespace.h> 44 45 #include <keys/dns_resolver-type.h> 46 #include <keys/user-type.h> 47 48 #include "internal.h" 49 50 /** 51 * dns_query - Query the DNS 52 * @net: The network namespace to operate in. 53 * @type: Query type (or NULL for straight host->IP lookup) 54 * @name: Name to look up 55 * @namelen: Length of name 56 * @options: Request options (or NULL if no options) 57 * @_result: Where to place the returned data (or NULL) 58 * @_expiry: Where to store the result expiry time (or NULL) 59 * @invalidate: Always invalidate the key after use 60 * 61 * The data will be returned in the pointer at *result, if provided, and the 62 * caller is responsible for freeing it. 63 * 64 * The description should be of the form "[<query_type>:]<domain_name>", and 65 * the options need to be appropriate for the query type requested. If no 66 * query_type is given, then the query is a straight hostname to IP address 67 * lookup. 68 * 69 * The DNS resolution lookup is performed by upcalling to userspace by way of 70 * requesting a key of type dns_resolver. 71 * 72 * Returns the size of the result on success, -ve error code otherwise. 73 */ 74 int dns_query(struct net *net, 75 const char *type, const char *name, size_t namelen, 76 const char *options, char **_result, time64_t *_expiry, 77 bool invalidate) 78 { 79 struct key *rkey; 80 struct user_key_payload *upayload; 81 const struct cred *saved_cred; 82 size_t typelen, desclen; 83 char *desc, *cp; 84 int ret, len; 85 86 kenter("%s,%*.*s,%zu,%s", 87 type, (int)namelen, (int)namelen, name, namelen, options); 88 89 if (!name || namelen == 0) 90 return -EINVAL; 91 92 /* construct the query key description as "[<type>:]<name>" */ 93 typelen = 0; 94 desclen = 0; 95 if (type) { 96 typelen = strlen(type); 97 if (typelen < 1) 98 return -EINVAL; 99 desclen += typelen + 1; 100 } 101 102 if (namelen < 3 || namelen > 255) 103 return -EINVAL; 104 desclen += namelen + 1; 105 106 desc = kmalloc(desclen, GFP_KERNEL); 107 if (!desc) 108 return -ENOMEM; 109 110 cp = desc; 111 if (type) { 112 memcpy(cp, type, typelen); 113 cp += typelen; 114 *cp++ = ':'; 115 } 116 memcpy(cp, name, namelen); 117 cp += namelen; 118 *cp = '\0'; 119 120 if (!options) 121 options = ""; 122 kdebug("call request_key(,%s,%s)", desc, options); 123 124 /* make the upcall, using special credentials to prevent the use of 125 * add_key() to preinstall malicious redirections 126 */ 127 saved_cred = override_creds(dns_resolver_cache); 128 rkey = request_key_net(&key_type_dns_resolver, desc, net, options); 129 revert_creds(saved_cred); 130 kfree(desc); 131 if (IS_ERR(rkey)) { 132 ret = PTR_ERR(rkey); 133 goto out; 134 } 135 136 down_read(&rkey->sem); 137 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); 138 rkey->perm |= KEY_USR_VIEW; 139 140 ret = key_validate(rkey); 141 if (ret < 0) 142 goto put; 143 144 /* If the DNS server gave an error, return that to the caller */ 145 ret = PTR_ERR(rkey->payload.data[dns_key_error]); 146 if (ret) 147 goto put; 148 149 upayload = user_key_payload_locked(rkey); 150 len = upayload->datalen; 151 152 if (_result) { 153 ret = -ENOMEM; 154 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL); 155 if (!*_result) 156 goto put; 157 } 158 159 if (_expiry) 160 *_expiry = rkey->expiry; 161 162 ret = len; 163 put: 164 up_read(&rkey->sem); 165 if (invalidate) 166 key_invalidate(rkey); 167 key_put(rkey); 168 out: 169 kleave(" = %d", ret); 170 return ret; 171 } 172 EXPORT_SYMBOL(dns_query); 173