dns_query.c | Explore in Territory

/* 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 ([email protected])
 *              Steve French ([email protected])
 *              Wang Lei ([email protected])
 *		David Howells ([email protected])
 *
 *   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
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 *   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 <http://www.gnu.org/licenses/>.
 */

#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)
{ … }
EXPORT_SYMBOL(…);
linux/net/dns_resolver/dns_query.c
