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.rst
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 */
dns_query(struct net * net,const char * type,const char * name,size_t namelen,const char * options,char ** _result,time64_t * _expiry,bool invalidate)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 size_t typelen, desclen;
82 char *desc, *cp;
83 int ret, len;
84
85 kenter("%s,%*.*s,%zu,%s",
86 type, (int)namelen, (int)namelen, name, namelen, options);
87
88 if (!name || namelen == 0)
89 return -EINVAL;
90
91 /* construct the query key description as "[<type>:]<name>" */
92 typelen = 0;
93 desclen = 0;
94 if (type) {
95 typelen = strlen(type);
96 if (typelen < 1)
97 return -EINVAL;
98 desclen += typelen + 1;
99 }
100
101 if (namelen < 3 || namelen > 255)
102 return -EINVAL;
103 desclen += namelen + 1;
104
105 desc = kmalloc(desclen, GFP_KERNEL);
106 if (!desc)
107 return -ENOMEM;
108
109 cp = desc;
110 if (type) {
111 memcpy(cp, type, typelen);
112 cp += typelen;
113 *cp++ = ':';
114 }
115 memcpy(cp, name, namelen);
116 cp += namelen;
117 *cp = '\0';
118
119 if (!options)
120 options = "";
121 kdebug("call request_key(,%s,%s)", desc, options);
122
123 /* make the upcall, using special credentials to prevent the use of
124 * add_key() to preinstall malicious redirections
125 */
126 scoped_with_creds(dns_resolver_cache)
127 rkey = request_key_net(&key_type_dns_resolver, desc, net, options);
128 kfree(desc);
129 if (IS_ERR(rkey)) {
130 ret = PTR_ERR(rkey);
131 goto out;
132 }
133
134 down_read(&rkey->sem);
135 set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
136 rkey->perm |= KEY_USR_VIEW;
137
138 ret = key_validate(rkey);
139 if (ret < 0)
140 goto put;
141
142 /* If the DNS server gave an error, return that to the caller */
143 ret = PTR_ERR(rkey->payload.data[dns_key_error]);
144 if (ret)
145 goto put;
146
147 upayload = user_key_payload_locked(rkey);
148 len = upayload->datalen;
149
150 if (_result) {
151 ret = -ENOMEM;
152 *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
153 if (!*_result)
154 goto put;
155 }
156
157 if (_expiry)
158 *_expiry = rkey->expiry;
159
160 ret = len;
161 put:
162 up_read(&rkey->sem);
163 if (invalidate)
164 key_invalidate(rkey);
165 key_put(rkey);
166 out:
167 kleave(" = %d", ret);
168 return ret;
169 }
170 EXPORT_SYMBOL(dns_query);
171