236 lines
5.4 KiB
C
236 lines
5.4 KiB
C
/*
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* fs/cifs/dns_resolve.c
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*
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* Copyright (c) 2007 Igor Mammedov
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* Author(s): Igor Mammedov (niallain@gmail.com)
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* Steve French (sfrench@us.ibm.com)
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*
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* Contains the CIFS DFS upcall routines used for hostname to
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* IP address translation.
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/slab.h>
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#include <linux/keyctl.h>
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#include <linux/key-type.h>
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#include <keys/user-type.h>
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#include "dns_resolve.h"
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#include "cifsglob.h"
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#include "cifsproto.h"
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#include "cifs_debug.h"
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static const struct cred *dns_resolver_cache;
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/* Checks if supplied name is IP address
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* returns:
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* 1 - name is IP
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* 0 - name is not IP
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*/
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static int
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is_ip(const char *name, int len)
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{
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struct sockaddr_storage ss;
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return cifs_convert_address((struct sockaddr *)&ss, name, len);
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}
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static int
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dns_resolver_instantiate(struct key *key, const void *data,
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size_t datalen)
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{
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int rc = 0;
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char *ip;
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/* make sure this looks like an address */
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if (!is_ip(data, datalen))
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return -EINVAL;
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ip = kmalloc(datalen + 1, GFP_KERNEL);
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if (!ip)
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return -ENOMEM;
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memcpy(ip, data, datalen);
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ip[datalen] = '\0';
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key->type_data.x[0] = datalen;
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key->payload.data = ip;
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return rc;
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}
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static void
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dns_resolver_destroy(struct key *key)
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{
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kfree(key->payload.data);
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}
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struct key_type key_type_dns_resolver = {
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.name = "dns_resolver",
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.def_datalen = sizeof(struct in_addr),
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.describe = user_describe,
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.instantiate = dns_resolver_instantiate,
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.destroy = dns_resolver_destroy,
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.match = user_match,
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};
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/* Resolves server name to ip address.
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* input:
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* unc - server UNC
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* output:
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* *ip_addr - pointer to server ip, caller responcible for freeing it.
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* return the length of the returned string on success
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*/
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int
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dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
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{
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const struct cred *saved_cred;
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int rc = -EAGAIN;
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struct key *rkey = ERR_PTR(-EAGAIN);
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char *name;
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char *data = NULL;
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int len;
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if (!ip_addr || !unc)
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return -EINVAL;
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/* search for server name delimiter */
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len = strlen(unc);
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if (len < 3) {
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cFYI(1, "%s: unc is too short: %s", __func__, unc);
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return -EINVAL;
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}
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len -= 2;
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name = memchr(unc+2, '\\', len);
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if (!name) {
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cFYI(1, "%s: probably server name is whole unc: %s",
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__func__, unc);
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} else {
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len = (name - unc) - 2/* leading // */;
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}
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name = kmalloc(len+1, GFP_KERNEL);
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if (!name) {
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rc = -ENOMEM;
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return rc;
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}
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memcpy(name, unc+2, len);
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name[len] = 0;
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if (is_ip(name, len)) {
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cFYI(1, "%s: it is IP, skipping dns upcall: %s",
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__func__, name);
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data = name;
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goto skip_upcall;
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}
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saved_cred = override_creds(dns_resolver_cache);
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rkey = request_key(&key_type_dns_resolver, name, "");
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revert_creds(saved_cred);
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if (!IS_ERR(rkey)) {
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if (!(rkey->perm & KEY_USR_VIEW)) {
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down_read(&rkey->sem);
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rkey->perm |= KEY_USR_VIEW;
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up_read(&rkey->sem);
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}
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len = rkey->type_data.x[0];
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data = rkey->payload.data;
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} else {
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cERROR(1, "%s: unable to resolve: %s", __func__, name);
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goto out;
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}
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skip_upcall:
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if (data) {
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*ip_addr = kmalloc(len + 1, GFP_KERNEL);
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if (*ip_addr) {
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memcpy(*ip_addr, data, len + 1);
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if (!IS_ERR(rkey))
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cFYI(1, "%s: resolved: %s to %s", __func__,
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name,
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*ip_addr
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);
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rc = len;
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} else {
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rc = -ENOMEM;
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}
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if (!IS_ERR(rkey))
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key_put(rkey);
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}
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out:
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kfree(name);
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return rc;
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}
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int __init cifs_init_dns_resolver(void)
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{
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struct cred *cred;
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struct key *keyring;
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int ret;
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printk(KERN_NOTICE "Registering the %s key type\n",
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key_type_dns_resolver.name);
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/* create an override credential set with a special thread keyring in
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* which DNS requests are cached
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*
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* this is used to prevent malicious redirections from being installed
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* with add_key().
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*/
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cred = prepare_kernel_cred(NULL);
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if (!cred)
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return -ENOMEM;
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keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
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(KEY_POS_ALL & ~KEY_POS_SETATTR) |
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KEY_USR_VIEW | KEY_USR_READ,
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KEY_ALLOC_NOT_IN_QUOTA);
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if (IS_ERR(keyring)) {
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ret = PTR_ERR(keyring);
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goto failed_put_cred;
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}
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ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
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if (ret < 0)
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goto failed_put_key;
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ret = register_key_type(&key_type_dns_resolver);
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if (ret < 0)
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goto failed_put_key;
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/* instruct request_key() to use this special keyring as a cache for
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* the results it looks up */
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cred->thread_keyring = keyring;
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cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
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dns_resolver_cache = cred;
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return 0;
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failed_put_key:
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key_put(keyring);
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failed_put_cred:
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put_cred(cred);
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return ret;
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}
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void cifs_exit_dns_resolver(void)
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{
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key_revoke(dns_resolver_cache->thread_keyring);
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unregister_key_type(&key_type_dns_resolver);
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put_cred(dns_resolver_cache);
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printk(KERN_NOTICE "Unregistered %s key type\n",
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key_type_dns_resolver.name);
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}
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