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 	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