dns_query.c

  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 */
 74int 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;
161put:
162	up_read(&rkey->sem);
163	if (invalidate)
164		key_invalidate(rkey);
165	key_put(rkey);
166out:
167	kleave(" = %d", ret);
168	return ret;
169}
170EXPORT_SYMBOL(dns_query);