1 /* Upcall routine, designed to work as a key type and working through
2 * /sbin/request-key to contact userspace when handling DNS queries.
4 * See Documentation/networking/dns_resolver.txt
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)
12 * The upcall wrapper used to make an arbitrary DNS query.
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:
18 * create dns_resolver * * /sbin/dns.upcall %k
20 * For example to use this module to query AFSDB RR:
22 * create dns_resolver afsdb:* * /sbin/dns.afsdb %k
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.
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.
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/>.
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>
45 #include <keys/dns_resolver-type.h>
46 #include <keys/user-type.h>
50 static struct key_acl dns_key_acl = {
51 .usage = REFCOUNT_INIT(1),
53 .possessor_viewable = true,
55 KEY_POSSESSOR_ACE(KEY_ACE_VIEW | KEY_ACE_SEARCH | KEY_ACE_READ),
56 KEY_OWNER_ACE(KEY_ACE_VIEW | KEY_ACE_INVAL),
61 * dns_query - Query the DNS
62 * @net: The network namespace to operate in.
63 * @type: Query type (or NULL for straight host->IP lookup)
64 * @name: Name to look up
65 * @namelen: Length of name
66 * @options: Request options (or NULL if no options)
67 * @_result: Where to place the returned data (or NULL)
68 * @_expiry: Where to store the result expiry time (or NULL)
69 * @invalidate: Always invalidate the key after use
71 * The data will be returned in the pointer at *result, if provided, and the
72 * caller is responsible for freeing it.
74 * The description should be of the form "[<query_type>:]<domain_name>", and
75 * the options need to be appropriate for the query type requested. If no
76 * query_type is given, then the query is a straight hostname to IP address
79 * The DNS resolution lookup is performed by upcalling to userspace by way of
80 * requesting a key of type dns_resolver.
82 * Returns the size of the result on success, -ve error code otherwise.
84 int dns_query(struct net *net,
85 const char *type, const char *name, size_t namelen,
86 const char *options, char **_result, time64_t *_expiry,
90 struct user_key_payload *upayload;
91 const struct cred *saved_cred;
92 size_t typelen, desclen;
96 kenter("%s,%*.*s,%zu,%s",
97 type, (int)namelen, (int)namelen, name, namelen, options);
99 if (!name || namelen == 0)
102 /* construct the query key description as "[<type>:]<name>" */
106 typelen = strlen(type);
109 desclen += typelen + 1;
112 if (namelen < 3 || namelen > 255)
114 desclen += namelen + 1;
116 desc = kmalloc(desclen, GFP_KERNEL);
122 memcpy(cp, type, typelen);
126 memcpy(cp, name, namelen);
132 kdebug("call request_key(,%s,%s)", desc, options);
134 /* make the upcall, using special credentials to prevent the use of
135 * add_key() to preinstall malicious redirections
137 saved_cred = override_creds(dns_resolver_cache);
138 rkey = request_key_net(&key_type_dns_resolver, desc, net, options,
140 revert_creds(saved_cred);
147 down_read(&rkey->sem);
148 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
149 ret = key_validate(rkey);
153 /* If the DNS server gave an error, return that to the caller */
154 ret = PTR_ERR(rkey->payload.data[dns_key_error]);
158 upayload = user_key_payload_locked(rkey);
159 len = upayload->datalen;
163 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
169 *_expiry = rkey->expiry;
175 key_invalidate(rkey);
178 kleave(" = %d", ret);
181 EXPORT_SYMBOL(dns_query);