1 // SPDX-License-Identifier: LGPL-2.1-or-later 2 /* Upcall routine, designed to work as a key type and working through 3 * /sbin/request-key to contact userspace when handling DNS queries. 4 * 5 * See Documentation/networking/dns_resolver.rst 6 * 7 * Copyright (c) 2007 Igor Mammedov 8 * Author(s): Igor Mammedov (niallain@gmail.com) 9 * Steve French (sfrench@us.ibm.com) 10 * Wang Lei (wang840925@gmail.com) 11 * David Howells (dhowells@redhat.com) 12 * 13 * The upcall wrapper used to make an arbitrary DNS query. 14 * 15 * This function requires the appropriate userspace tool dns.upcall to be 16 * installed and something like the following lines should be added to the 17 * /etc/request-key.conf file: 18 * 19 * create dns_resolver * * /sbin/dns.upcall %k 20 * 21 * For example to use this module to query AFSDB RR: 22 * 23 * create dns_resolver afsdb:* * /sbin/dns.afsdb %k 24 */ 25 26 #include <linux/module.h> 27 #include <linux/slab.h> 28 #include <linux/cred.h> 29 #include <linux/dns_resolver.h> 30 #include <linux/err.h> 31 #include <net/net_namespace.h> 32 33 #include <keys/dns_resolver-type.h> 34 #include <keys/user-type.h> 35 36 #include "internal.h" 37 38 /** 39 * dns_query - Query the DNS 40 * @net: The network namespace to operate in. 41 * @type: Query type (or NULL for straight host->IP lookup) 42 * @name: Name to look up 43 * @namelen: Length of name 44 * @options: Request options (or NULL if no options) 45 * @_result: Where to place the returned data (or NULL) 46 * @_expiry: Where to store the result expiry time (or NULL) 47 * @invalidate: Always invalidate the key after use 48 * 49 * The data will be returned in the pointer at *result, if provided, and the 50 * caller is responsible for freeing it. 51 * 52 * The description should be of the form "[<query_type>:]<domain_name>", and 53 * the options need to be appropriate for the query type requested. If no 54 * query_type is given, then the query is a straight hostname to IP address 55 * lookup. 56 * 57 * The DNS resolution lookup is performed by upcalling to userspace by way of 58 * requesting a key of type dns_resolver. 59 * 60 * Returns the size of the result on success, -ve error code otherwise. 61 */ 62 int dns_query(struct net *net, 63 const char *type, const char *name, size_t namelen, 64 const char *options, char **_result, time64_t *_expiry, 65 bool invalidate) 66 { 67 struct key *rkey; 68 struct user_key_payload *upayload; 69 size_t typelen, desclen; 70 char *desc, *cp; 71 int ret, len; 72 73 kenter("%s,%*.*s,%zu,%s", 74 type, (int)namelen, (int)namelen, name, namelen, options); 75 76 if (!name || namelen == 0) 77 return -EINVAL; 78 79 /* construct the query key description as "[<type>:]<name>" */ 80 typelen = 0; 81 desclen = 0; 82 if (type) { 83 typelen = strlen(type); 84 if (typelen < 1) 85 return -EINVAL; 86 desclen += typelen + 1; 87 } 88 89 if (namelen < 3 || namelen > 255) 90 return -EINVAL; 91 desclen += namelen + 1; 92 93 desc = kmalloc(desclen, GFP_KERNEL); 94 if (!desc) 95 return -ENOMEM; 96 97 cp = desc; 98 if (type) { 99 memcpy(cp, type, typelen); 100 cp += typelen; 101 *cp++ = ':'; 102 } 103 memcpy(cp, name, namelen); 104 cp += namelen; 105 *cp = '\0'; 106 107 if (!options) 108 options = ""; 109 kdebug("call request_key(,%s,%s)", desc, options); 110 111 /* make the upcall, using special credentials to prevent the use of 112 * add_key() to preinstall malicious redirections 113 */ 114 scoped_with_creds(dns_resolver_cache) 115 rkey = request_key_net(&key_type_dns_resolver, desc, net, options); 116 kfree(desc); 117 if (IS_ERR(rkey)) { 118 ret = PTR_ERR(rkey); 119 goto out; 120 } 121 122 down_read(&rkey->sem); 123 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); 124 rkey->perm |= KEY_USR_VIEW; 125 126 ret = key_validate(rkey); 127 if (ret < 0) 128 goto put; 129 130 /* If the DNS server gave an error, return that to the caller */ 131 ret = PTR_ERR(rkey->payload.data[dns_key_error]); 132 if (ret) 133 goto put; 134 135 upayload = user_key_payload_locked(rkey); 136 len = upayload->datalen; 137 138 if (_result) { 139 ret = -ENOMEM; 140 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL); 141 if (!*_result) 142 goto put; 143 } 144 145 if (_expiry) 146 *_expiry = rkey->expiry; 147 148 ret = len; 149 put: 150 up_read(&rkey->sem); 151 if (invalidate) 152 key_invalidate(rkey); 153 key_put(rkey); 154 out: 155 kleave(" = %d", ret); 156 return ret; 157 } 158 EXPORT_SYMBOL(dns_query); 159