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/*
* fs/cifs/dns_resolve.c
*
* Copyright (c) 2007 Igor Mammedov
* Author(s): Igor Mammedov (niallain@gmail.com)
* Steve French (sfrench@us.ibm.com)
*
* Contains the CIFS DFS upcall routines used for hostname to
* IP address translation.
*
* 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/slab.h>
#include <linux/keyctl.h>
#include <linux/key-type.h>
#include <keys/user-type.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(char *name)
{
struct sockaddr_storage ss;
return cifs_convert_address(name, &ss);
}
static int
dns_resolver_instantiate(struct key *key, const void *data,
size_t datalen)
{
int rc = 0;
char *ip;
ip = kmalloc(datalen + 1, GFP_KERNEL);
if (!ip)
return -ENOMEM;
memcpy(ip, data, datalen);
ip[datalen] = '\0';
/* make sure this looks like an address */
if (!is_ip(ip)) {
kfree(ip);
return -EINVAL;
}
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 0 on success
*/
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);
char *name;
char *data = NULL;
int len;
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)) {
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 = 0;
} else {
rc = -ENOMEM;
}
if (!IS_ERR(rkey))
key_put(rkey);
}
out:
kfree(name);
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)
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;
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);
}
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