dns_resolve.c
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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)
* Wang Lei (wang840925@gmail.com)
* David Howells (dhowells@redhat.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/dns_resolver.h>
#include "dns_resolve.h"
#include "cifsglob.h"
#include "cifsproto.h"
#include "cifs_debug.h"
/**
* dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
* @unc: UNC path specifying the server (with '/' as delimiter)
* @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)
{
struct sockaddr_storage ss;
const char *hostname, *sep;
char *name;
int len, rc;
if (!ip_addr || !unc)
return -EINVAL;
len = strlen(unc);
if (len < 3) {
cifs_dbg(FYI, "%s: unc is too short: %s\n", __func__, unc);
return -EINVAL;
}
/* Discount leading slashes for cifs */
len -= 2;
hostname = unc + 2;
/* Search for server name delimiter */
sep = memchr(hostname, '/', len);
if (sep)
len = sep - hostname;
else
cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
__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)
cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
__func__, len, len, hostname);
else
cifs_dbg(FYI, "%s: resolved: %*.*s to %s\n",
__func__, len, len, hostname, *ip_addr);
return rc;
name_is_IP_address:
name = kmalloc(len + 1, GFP_KERNEL);
if (!name)
return -ENOMEM;
memcpy(name, hostname, len);
name[len] = 0;
cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s\n",
__func__, name);
*ip_addr = name;
return 0;
}