Commit 1a4240f4 authored by Wang Lei's avatar Wang Lei Committed by Steve French

DNS: Separate out CIFS DNS Resolver code

Separate out the DNS resolver key type from the CIFS filesystem into its own
module so that it can be made available for general use, including the AFS
filesystem module.

This facility makes it possible for the kernel to upcall to userspace to have
it issue DNS requests, package up the replies and present them to the kernel
in a useful form.  The kernel is then able to cache the DNS replies as keys
can be retained in keyrings.

Resolver keys are of type "dns_resolver" and have a case-insensitive
description that is of the form "[<type>:]<domain_name>".  The optional <type>
indicates the particular DNS lookup and packaging that's required.  The
<domain_name> is the query to be made.

If <type> isn't given, a basic hostname to IP address lookup is made, and the
result is stored in the key in the form of a printable string consisting of a
comma-separated list of IPv4 and IPv6 addresses.

This key type is supported by userspace helpers driven from /sbin/request-key
and configured through /etc/request-key.conf.  The cifs.upcall utility is
invoked for UNC path server name to IP address resolution.

The CIFS functionality is encapsulated by the dns_resolve_unc_to_ip() function,
which is used to resolve a UNC path to an IP address for CIFS filesystem.  This
part remains in the CIFS module for now.

See the added Documentation/networking/dns_resolver.txt for more information.
Signed-off-by: default avatarWang Lei <wang840925@gmail.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Acked-by: default avatarJeff Layton <jlayton@redhat.com>
Signed-off-by: default avatarSteve French <sfrench@us.ibm.com>
parent ba5dadbf
===================
DNS Resolver Module
===================
Contents:
- Overview.
- Compilation.
- Setting up.
- Usage.
- Mechanism.
- Debugging.
========
OVERVIEW
========
The DNS resolver module provides a way for kernel services to make DNS queries
by way of requesting a key of key type dns_resolver. These queries are
upcalled to userspace through /sbin/request-key.
These routines must be supported by userspace tools dns.upcall, cifs.upcall and
request-key. It is under development and does not yet provide the full feature
set. The features it does support include:
(*) Implements the dns_resolver key_type to contact userspace.
It does not yet support the following AFS features:
(*) Dns query support for AFSDB resource record.
This code is extracted from the CIFS filesystem.
===========
COMPILATION
===========
The module should be enabled by turning on the kernel configuration options:
CONFIG_DNS_RESOLVER - tristate "DNS Resolver support"
==========
SETTING UP
==========
To set up this facility, the /etc/request-key.conf file must be altered so that
/sbin/request-key can appropriately direct the upcalls. For example, to handle
basic dname to IPv4/IPv6 address resolution, the following line should be
added:
#OP TYPE DESC CO-INFO PROGRAM ARG1 ARG2 ARG3 ...
#====== ============ ======= ======= ==========================
create dns_resolver * * /usr/sbin/cifs.upcall %k
To direct a query for query type 'foo', a line of the following should be added
before the more general line given above as the first match is the one taken.
create dns_resolver foo:* * /usr/sbin/dns.foo %k
=====
USAGE
=====
To make use of this facility, one of the following functions that are
implemented in the module can be called after doing:
#include <linux/dns_resolver.h>
(1) int dns_query(const char *type, const char *name, size_t namelen,
const char *options, char **_result, time_t *_expiry);
This is the basic access function. It looks for a cached DNS query and if
it doesn't find it, it upcalls to userspace to make a new DNS query, which
may then be cached. The key description is constructed as a string of the
form:
[<type>:]<name>
where <type> optionally specifies the particular upcall program to invoke,
and thus the type of query to do, and <name> specifies the string to be
looked up. The default query type is a straight hostname to IP address
set lookup.
The name parameter is not required to be a NUL-terminated string, and its
length should be given by the namelen argument.
The options parameter may be NULL or it may be a set of options
appropriate to the query type.
The return value is a string appropriate to the query type. For instance,
for the default query type it is just a list of comma-separated IPv4 and
IPv6 addresses. The caller must free the result.
The length of the result string is returned on success, and a -ve error
code is returned otherwise. -EKEYREJECTED will be returned if the DNS
lookup failed.
If _expiry is non-NULL, the expiry time (TTL) of the result will be
returned also.
=========
MECHANISM
=========
The dnsresolver module registers a key type called "dns_resolver". Keys of
this type are used to transport and cache DNS lookup results from userspace.
When dns_query() is invoked, it calls request_key() to search the local
keyrings for a cached DNS result. If that fails to find one, it upcalls to
userspace to get a new result.
Upcalls to userspace are made through the request_key() upcall vector, and are
directed by means of configuration lines in /etc/request-key.conf that tell
/sbin/request-key what program to run to instantiate the key.
The upcall handler program is responsible for querying the DNS, processing the
result into a form suitable for passing to the keyctl_instantiate_key()
routine. This then passes the data to dns_resolver_instantiate() which strips
off and processes any options included in the data, and then attaches the
remainder of the string to the key as its payload.
The upcall handler program should set the expiry time on the key to that of the
lowest TTL of all the records it has extracted a result from. This means that
the key will be discarded and recreated when the data it holds has expired.
dns_query() returns a copy of the value attached to the key, or an error if
that is indicated instead.
See <file:Documentation/keys-request-key.txt> for further information about
request-key function.
=========
DEBUGGING
=========
Debugging messages can be turned on dynamically by writing a 1 into the
following file:
/sys/module/dnsresolver/parameters/debug
......@@ -71,14 +71,14 @@ config CIFS_WEAK_PW_HASH
If unsure, say N.
config CIFS_UPCALL
bool "Kerberos/SPNEGO advanced session setup"
depends on CIFS && KEYS
help
Enables an upcall mechanism for CIFS which accesses
userspace helper utilities to provide SPNEGO packaged (RFC 4178)
Kerberos tickets which are needed to mount to certain secure servers
(for which more secure Kerberos authentication is required). If
unsure, say N.
bool "Kerberos/SPNEGO advanced session setup"
depends on CIFS && KEYS
select DNS_RESOLVER
help
Enables an upcall mechanism for CIFS which accesses userspace helper
utilities to provide SPNEGO packaged (RFC 4178) Kerberos tickets
which are needed to mount to certain secure servers (for which more
secure Kerberos authentication is required). If unsure, say N.
config CIFS_XATTR
bool "CIFS extended attributes"
......@@ -122,6 +122,7 @@ config CIFS_DEBUG2
config CIFS_DFS_UPCALL
bool "DFS feature support"
depends on CIFS && KEYS
select DNS_RESOLVER
help
Distributed File System (DFS) support is used to access shares
transparently in an enterprise name space, even if the share
......
......@@ -45,7 +45,6 @@
#include "cifs_fs_sb.h"
#include <linux/mm.h>
#include <linux/key-type.h>
#include "dns_resolve.h"
#include "cifs_spnego.h"
#include "fscache.h"
#define CIFS_MAGIC_NUMBER 0xFF534D42 /* the first four bytes of SMB PDUs */
......@@ -933,23 +932,14 @@ init_cifs(void)
rc = register_key_type(&cifs_spnego_key_type);
if (rc)
goto out_unregister_filesystem;
#endif
#ifdef CONFIG_CIFS_DFS_UPCALL
rc = cifs_init_dns_resolver();
if (rc)
goto out_unregister_key_type;
#endif
rc = slow_work_register_user(THIS_MODULE);
if (rc)
goto out_unregister_resolver_key;
goto out_unregister_key_type;
return 0;
out_unregister_resolver_key:
#ifdef CONFIG_CIFS_DFS_UPCALL
cifs_exit_dns_resolver();
out_unregister_key_type:
#endif
#ifdef CONFIG_CIFS_UPCALL
unregister_key_type(&cifs_spnego_key_type);
out_unregister_filesystem:
......@@ -976,7 +966,6 @@ exit_cifs(void)
cifs_fscache_unregister();
#ifdef CONFIG_CIFS_DFS_UPCALL
cifs_dfs_release_automount_timer();
cifs_exit_dns_resolver();
#endif
#ifdef CONFIG_CIFS_UPCALL
unregister_key_type(&cifs_spnego_key_type);
......
......@@ -4,6 +4,8 @@
* Copyright (c) 2007 Igor Mammedov
* Author(s): Igor Mammedov (niallain@gmail.com)
* Steve French (sfrench@us.ibm.com)
* Wang Lei (wang840925@gmail.com)
* David Howells (dhowells@redhat.com)
*
* Contains the CIFS DFS upcall routines used for hostname to
* IP address translation.
......@@ -24,212 +26,73 @@
*/
#include <linux/slab.h>
#include <linux/keyctl.h>
#include <linux/key-type.h>
#include <keys/user-type.h>
#include <linux/dns_resolver.h>
#include "dns_resolve.h"
#include "cifsglob.h"
#include "cifsproto.h"
#include "cifs_debug.h"
static const struct cred *dns_resolver_cache;
/* Checks if supplied name is IP address
* returns:
* 1 - name is IP
* 0 - name is not IP
*/
static int
is_ip(const char *name, int len)
{
struct sockaddr_storage ss;
return cifs_convert_address((struct sockaddr *)&ss, name, len);
}
static int
dns_resolver_instantiate(struct key *key, const void *data,
size_t datalen)
{
int rc = 0;
char *ip;
/* make sure this looks like an address */
if (!is_ip(data, datalen))
return -EINVAL;
ip = kmalloc(datalen + 1, GFP_KERNEL);
if (!ip)
return -ENOMEM;
memcpy(ip, data, datalen);
ip[datalen] = '\0';
key->type_data.x[0] = datalen;
key->payload.data = ip;
return rc;
}
static void
dns_resolver_destroy(struct key *key)
{
kfree(key->payload.data);
}
struct key_type key_type_dns_resolver = {
.name = "dns_resolver",
.def_datalen = sizeof(struct in_addr),
.describe = user_describe,
.instantiate = dns_resolver_instantiate,
.destroy = dns_resolver_destroy,
.match = user_match,
};
/* Resolves server name to ip address.
* input:
* unc - server UNC
* output:
* *ip_addr - pointer to server ip, caller responcible for freeing it.
* return the length of the returned string on success
/**
* dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
* @unc: UNC path specifying the server
* @ip_addr: Where to return the IP address.
*
* The IP address will be returned in string form, and the caller is
* responsible for freeing it.
*
* Returns length of result on success, -ve on error.
*/
int
dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
{
const struct cred *saved_cred;
int rc = -EAGAIN;
struct key *rkey = ERR_PTR(-EAGAIN);
struct sockaddr_storage ss;
const char *hostname, *sep;
char *name;
char *data = NULL;
int len;
int len, rc;
if (!ip_addr || !unc)
return -EINVAL;
/* search for server name delimiter */
len = strlen(unc);
if (len < 3) {
cFYI(1, "%s: unc is too short: %s", __func__, unc);
return -EINVAL;
}
len -= 2;
name = memchr(unc+2, '\\', len);
if (!name) {
cFYI(1, "%s: probably server name is whole unc: %s",
__func__, unc);
} else {
len = (name - unc) - 2/* leading // */;
}
name = kmalloc(len+1, GFP_KERNEL);
if (!name) {
rc = -ENOMEM;
return rc;
}
memcpy(name, unc+2, len);
name[len] = 0;
if (is_ip(name, len)) {
cFYI(1, "%s: it is IP, skipping dns upcall: %s",
__func__, name);
data = name;
goto skip_upcall;
}
saved_cred = override_creds(dns_resolver_cache);
rkey = request_key(&key_type_dns_resolver, name, "");
revert_creds(saved_cred);
if (!IS_ERR(rkey)) {
if (!(rkey->perm & KEY_USR_VIEW)) {
down_read(&rkey->sem);
rkey->perm |= KEY_USR_VIEW;
up_read(&rkey->sem);
}
len = rkey->type_data.x[0];
data = rkey->payload.data;
} else {
cERROR(1, "%s: unable to resolve: %s", __func__, name);
goto out;
}
skip_upcall:
if (data) {
*ip_addr = kmalloc(len + 1, GFP_KERNEL);
if (*ip_addr) {
memcpy(*ip_addr, data, len + 1);
if (!IS_ERR(rkey))
cFYI(1, "%s: resolved: %s to %s", __func__,
name,
*ip_addr
);
rc = len;
} else {
rc = -ENOMEM;
}
if (!IS_ERR(rkey))
key_put(rkey);
}
/* Discount leading slashes for cifs */
len -= 2;
hostname = unc + 2;
out:
kfree(name);
/* Search for server name delimiter */
sep = memchr(hostname, '\\', len);
if (sep)
len = sep - unc;
else
cFYI(1, "%s: probably server name is whole unc: %s",
__func__, unc);
/* Try to interpret hostname as an IPv4 or IPv6 address */
rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
if (rc > 0)
goto name_is_IP_address;
/* Perform the upcall */
rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
if (rc < 0)
cERROR(1, "%s: unable to resolve: %*.*s",
__func__, len, len, hostname);
else
cFYI(1, "%s: resolved: %*.*s to %s",
__func__, len, len, hostname, *ip_addr);
return rc;
}
int __init cifs_init_dns_resolver(void)
{
struct cred *cred;
struct key *keyring;
int ret;
printk(KERN_NOTICE "Registering the %s key type\n",
key_type_dns_resolver.name);
/* create an override credential set with a special thread keyring in
* which DNS requests are cached
*
* this is used to prevent malicious redirections from being installed
* with add_key().
*/
cred = prepare_kernel_cred(NULL);
if (!cred)
name_is_IP_address:
name = kmalloc(len + 1, GFP_KERNEL);
if (!name)
return -ENOMEM;
keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
(KEY_POS_ALL & ~KEY_POS_SETATTR) |
KEY_USR_VIEW | KEY_USR_READ,
KEY_ALLOC_NOT_IN_QUOTA);
if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto failed_put_cred;
}
ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
if (ret < 0)
goto failed_put_key;
ret = register_key_type(&key_type_dns_resolver);
if (ret < 0)
goto failed_put_key;
/* instruct request_key() to use this special keyring as a cache for
* the results it looks up */
cred->thread_keyring = keyring;
cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
dns_resolver_cache = cred;
memcpy(name, hostname, len);
name[len] = 0;
cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
*ip_addr = name;
return 0;
failed_put_key:
key_put(keyring);
failed_put_cred:
put_cred(cred);
return ret;
}
void cifs_exit_dns_resolver(void)
{
key_revoke(dns_resolver_cache->thread_keyring);
unregister_key_type(&key_type_dns_resolver);
put_cred(dns_resolver_cache);
printk(KERN_NOTICE "Unregistered %s key type\n",
key_type_dns_resolver.name);
}
......@@ -24,8 +24,6 @@
#define _DNS_RESOLVE_H
#ifdef __KERNEL__
extern int __init cifs_init_dns_resolver(void);
extern void cifs_exit_dns_resolver(void);
extern int dns_resolve_server_name_to_ip(const char *unc, char **ip_addr);
#endif /* KERNEL */
......
/* DNS resolver key type
*
* Copyright (C) 2010 Wang Lei. All Rights Reserved.
* Written by Wang Lei (wang840925@gmail.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#ifndef _KEYS_DNS_RESOLVER_TYPE_H
#define _KEYS_DNS_RESOLVER_TYPE_H
#include <linux/key-type.h>
extern struct key_type key_type_dns_resolver;
extern int request_dns_resolver_key(const char *description,
const char *callout_info,
char **data);
#endif /* _KEYS_DNS_RESOLVER_TYPE_H */
/*
* DNS Resolver upcall management for CIFS DFS and AFS
* Handles host name to IP address resolution and DNS query for AFSDB RR.
*
* Copyright (c) International Business Machines Corp., 2008
* Author(s): Steve French (sfrench@us.ibm.com)
* Wang Lei (wang840925@gmail.com)
*
* 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, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef _LINUX_DNS_RESOLVER_H
#define _LINUX_DNS_RESOLVER_H
#ifdef __KERNEL__
extern int dns_query(const char *type, const char *name, size_t namelen,
const char *options, char **_result, time_t *_expiry);
#endif /* KERNEL */
#endif /* _LINUX_DNS_RESOLVER_H */
......@@ -213,6 +213,7 @@ source "net/phonet/Kconfig"
source "net/ieee802154/Kconfig"
source "net/sched/Kconfig"
source "net/dcb/Kconfig"
source "net/dns_resolver/Kconfig"
config RPS
boolean
......
......@@ -67,3 +67,4 @@ ifeq ($(CONFIG_NET),y)
obj-$(CONFIG_SYSCTL) += sysctl_net.o
endif
obj-$(CONFIG_WIMAX) += wimax/
obj-$(CONFIG_DNS_RESOLVER) += dns_resolver/
#
# Configuration for DNS Resolver
#
config DNS_RESOLVER
tristate "DNS Resolver support"
depends on NET && KEYS
help
Saying Y here will include support for the DNS Resolver key type
which can be used to make upcalls to perform DNS lookups in
userspace.
DNS Resolver is used to query DNS server for information. Examples
being resolving a UNC hostname element to an IP address for CIFS or
performing a DNS query for AFSDB records so that AFS can locate a
cell's volume location database servers.
DNS Resolver is used by the CIFS and AFS modules, and would support
samba4 later. DNS Resolver is supported by the userspace upcall
helper "/sbin/dns.resolver" via /etc/request-key.conf.
See <file:Documentation/networking/dns_resolver.txt> for further
information.
To compile this as a module, choose M here: the module will be called
dnsresolver.
If unsure, say N.
#
# Makefile for the Linux DNS Resolver.
#
obj-$(CONFIG_DNS_RESOLVER) += dns_resolver.o
dns_resolver-objs := dns_key.o dns_query.o
/* Key type used to cache DNS lookups made by the kernel
*
* See Documentation/networking/dns_resolver.txt
*
* Copyright (c) 2007 Igor Mammedov
* Author(s): Igor Mammedov (niallain@gmail.com)
* Steve French (sfrench@us.ibm.com)
* Wang Lei (wang840925@gmail.com)
* David Howells (dhowells@redhat.com)
*
* 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, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/keyctl.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>
#include "internal.h"
MODULE_DESCRIPTION("DNS Resolver");
MODULE_AUTHOR("Wang Lei");
MODULE_LICENSE("GPL");
unsigned dns_resolver_debug;
module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
const struct cred *dns_resolver_cache;
/*
* Instantiate a user defined key for dns_resolver.
*
* The data must be a NUL-terminated string, with the NUL char accounted in
* datalen.
*
* If the data contains a '#' characters, then we take the clause after each
* one to be an option of the form 'key=value'. The actual data of interest is
* the string leading up to the first '#'. For instance:
*
* "ip1,ip2,...#foo=bar"
*/
static int
dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
{
struct user_key_payload *upayload;
int ret;
size_t result_len = 0;
const char *data = _data, *opt;
kenter("%%%d,%s,'%s',%zu",
key->serial, key->description, data, datalen);
if (datalen <= 1 || !data || data[datalen - 1] != '\0')
return -EINVAL;
datalen--;
/* deal with any options embedded in the data */
opt = memchr(data, '#', datalen);
if (!opt) {
kdebug("no options currently supported");
return -EINVAL;
}
result_len = datalen;
ret = key_payload_reserve(key, result_len);
if (ret < 0)
return -EINVAL;
upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
if (!upayload) {
kleave(" = -ENOMEM");
return -ENOMEM;
}
upayload->datalen = result_len;
memcpy(upayload->data, data, result_len);
upayload->data[result_len] = '\0';
rcu_assign_pointer(key->payload.data, upayload);
kleave(" = 0");
return 0;
}
/*
* The description is of the form "[<type>:]<domain_name>"
*
* The domain name may be a simple name or an absolute domain name (which
* should end with a period). The domain name is case-independent.
*/
static int
dns_resolver_match(const struct key *key, const void *description)
{
int slen, dlen, ret = 0;
const char *src = key->description, *dsp = description;
kenter("%s,%s", src, dsp);
if (!src || !dsp)
goto no_match;
if (strcasecmp(src, dsp) == 0)
goto matched;
slen = strlen(src);
dlen = strlen(dsp);
if (slen <= 0 || dlen <= 0)
goto no_match;
if (src[slen - 1] == '.')
slen--;
if (dsp[dlen - 1] == '.')
dlen--;
if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
goto no_match;
matched:
ret = 1;
no_match:
kleave(" = %d", ret);