blob: 82b084cc1cc6349bb532d5ada555b0bcbb1cdbea [file] [log] [blame]
/* Upcall routine, designed to work as a key type and working through
* /sbin/request-key to contact userspace when handling DNS queries.
* See Documentation/networking/dns_resolver.rst
* Copyright (c) 2007 Igor Mammedov
* Author(s): Igor Mammedov (
* Steve French (
* Wang Lei (
* David Howells (
* The upcall wrapper used to make an arbitrary DNS query.
* This function requires the appropriate userspace tool dns.upcall to be
* installed and something like the following lines should be added to the
* /etc/request-key.conf file:
* create dns_resolver * * /sbin/dns.upcall %k
* For example to use this module to query AFSDB RR:
* create dns_resolver afsdb:* * /sbin/dns.afsdb %k
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* the GNU Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, see <>.
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/dns_resolver.h>
#include <linux/err.h>
#include <net/net_namespace.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>
#include "internal.h"
* dns_query - Query the DNS
* @net: The network namespace to operate in.
* @type: Query type (or NULL for straight host->IP lookup)
* @name: Name to look up
* @namelen: Length of name
* @options: Request options (or NULL if no options)
* @_result: Where to place the returned data (or NULL)
* @_expiry: Where to store the result expiry time (or NULL)
* @invalidate: Always invalidate the key after use
* The data will be returned in the pointer at *result, if provided, and the
* caller is responsible for freeing it.
* The description should be of the form "[<query_type>:]<domain_name>", and
* the options need to be appropriate for the query type requested. If no
* query_type is given, then the query is a straight hostname to IP address
* lookup.
* The DNS resolution lookup is performed by upcalling to userspace by way of
* requesting a key of type dns_resolver.
* Returns the size of the result on success, -ve error code otherwise.
int dns_query(struct net *net,
const char *type, const char *name, size_t namelen,
const char *options, char **_result, time64_t *_expiry,
bool invalidate)
struct key *rkey;
struct user_key_payload *upayload;
const struct cred *saved_cred;
size_t typelen, desclen;
char *desc, *cp;
int ret, len;
type, (int)namelen, (int)namelen, name, namelen, options);
if (!name || namelen == 0)
return -EINVAL;
/* construct the query key description as "[<type>:]<name>" */
typelen = 0;
desclen = 0;
if (type) {
typelen = strlen(type);
if (typelen < 1)
return -EINVAL;
desclen += typelen + 1;
if (namelen < 3 || namelen > 255)
return -EINVAL;
desclen += namelen + 1;
desc = kmalloc(desclen, GFP_KERNEL);
if (!desc)
return -ENOMEM;
cp = desc;
if (type) {
memcpy(cp, type, typelen);
cp += typelen;
*cp++ = ':';
memcpy(cp, name, namelen);
cp += namelen;
*cp = '\0';
if (!options)
options = "";
kdebug("call request_key(,%s,%s)", desc, options);
/* make the upcall, using special credentials to prevent the use of
* add_key() to preinstall malicious redirections
saved_cred = override_creds(dns_resolver_cache);
rkey = request_key_net(&key_type_dns_resolver, desc, net, options);
if (IS_ERR(rkey)) {
ret = PTR_ERR(rkey);
goto out;
set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
rkey->perm |= KEY_USR_VIEW;
ret = key_validate(rkey);
if (ret < 0)
goto put;
/* If the DNS server gave an error, return that to the caller */
ret = PTR_ERR(rkey->[dns_key_error]);
if (ret)
goto put;
upayload = user_key_payload_locked(rkey);
len = upayload->datalen;
if (_result) {
ret = -ENOMEM;
*_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
if (!*_result)
goto put;
if (_expiry)
*_expiry = rkey->expiry;
ret = len;
if (invalidate)
kleave(" = %d", ret);
return ret;