blob: 03d5255f5cf2a08cd4a1efe8d4a57638d5c15f65 [file] [log] [blame]
Wang Lei1a4240f2010-08-04 15:16:33 +01001/* 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, write to the Free Software
36 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
37 */
38
39#include <linux/module.h>
40#include <linux/slab.h>
41#include <linux/dns_resolver.h>
Stephen Rothwellaf352fe2010-08-06 03:13:47 +010042#include <linux/err.h>
Wang Lei1a4240f2010-08-04 15:16:33 +010043#include <keys/dns_resolver-type.h>
44#include <keys/user-type.h>
45
46#include "internal.h"
47
David Howellsff9517a2010-08-06 03:13:52 +010048/**
Wang Lei1a4240f2010-08-04 15:16:33 +010049 * dns_query - Query the DNS
50 * @type: Query type (or NULL for straight host->IP lookup)
51 * @name: Name to look up
52 * @namelen: Length of name
53 * @options: Request options (or NULL if no options)
54 * @_result: Where to place the returned data.
55 * @_expiry: Where to store the result expiry time (or NULL)
56 *
57 * The data will be returned in the pointer at *result, and the caller is
58 * responsible for freeing it.
59 *
60 * The description should be of the form "[<query_type>:]<domain_name>", and
61 * the options need to be appropriate for the query type requested. If no
62 * query_type is given, then the query is a straight hostname to IP address
63 * lookup.
64 *
65 * The DNS resolution lookup is performed by upcalling to userspace by way of
66 * requesting a key of type dns_resolver.
67 *
68 * Returns the size of the result on success, -ve error code otherwise.
69 */
70int dns_query(const char *type, const char *name, size_t namelen,
71 const char *options, char **_result, time_t *_expiry)
72{
73 struct key *rkey;
74 struct user_key_payload *upayload;
75 const struct cred *saved_cred;
76 size_t typelen, desclen;
77 char *desc, *cp;
78 int ret, len;
79
80 kenter("%s,%*.*s,%zu,%s",
81 type, (int)namelen, (int)namelen, name, namelen, options);
82
83 if (!name || namelen == 0 || !_result)
84 return -EINVAL;
85
86 /* construct the query key description as "[<type>:]<name>" */
87 typelen = 0;
88 desclen = 0;
89 if (type) {
90 typelen = strlen(type);
91 if (typelen < 1)
92 return -EINVAL;
93 desclen += typelen + 1;
94 }
95
96 if (!namelen)
97 namelen = strlen(name);
98 if (namelen < 3)
99 return -EINVAL;
100 desclen += namelen + 1;
101
102 desc = kmalloc(desclen, GFP_KERNEL);
103 if (!desc)
104 return -ENOMEM;
105
106 cp = desc;
107 if (type) {
108 memcpy(cp, type, typelen);
109 cp += typelen;
110 *cp++ = ':';
111 }
112 memcpy(cp, name, namelen);
113 cp += namelen;
114 *cp = '\0';
115
116 if (!options)
117 options = "";
118 kdebug("call request_key(,%s,%s)", desc, options);
119
120 /* make the upcall, using special credentials to prevent the use of
121 * add_key() to preinstall malicious redirections
122 */
123 saved_cred = override_creds(dns_resolver_cache);
124 rkey = request_key(&key_type_dns_resolver, desc, options);
125 revert_creds(saved_cred);
126 kfree(desc);
127 if (IS_ERR(rkey)) {
128 ret = PTR_ERR(rkey);
129 goto out;
130 }
131
132 down_read(&rkey->sem);
133 rkey->perm |= KEY_USR_VIEW;
134
135 ret = key_validate(rkey);
136 if (ret < 0)
137 goto put;
138
139 upayload = rcu_dereference_protected(rkey->payload.data,
140 lockdep_is_held(&rkey->sem));
141 len = upayload->datalen;
142
143 ret = -ENOMEM;
144 *_result = kmalloc(len + 1, GFP_KERNEL);
145 if (!*_result)
146 goto put;
147
148 memcpy(*_result, upayload->data, len + 1);
149 if (_expiry)
150 *_expiry = rkey->expiry;
151
152 ret = len;
153put:
154 up_read(&rkey->sem);
155 key_put(rkey);
156out:
157 kleave(" = %d", ret);
158 return ret;
159}
160EXPORT_SYMBOL(dns_query);