dns_resolve.c

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/*
 *  fs/cifs/dns_resolve.c
 *
 *   Copyright (c) 2007 Igor Mammedov
 *   Author(s): Igor Mammedov ([email protected])
 *              Steve French ([email protected])
 *              Wang Lei ([email protected])
 *      David Howells ([email protected])
 *
 *   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"

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) {
        cFYI(1, "%s: unc is too short: %s", __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
        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)
        cFYI(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;

name_is_IP_address:
    name = kmalloc(len + 1, GFP_KERNEL);
    if (!name)
        return -ENOMEM;
    memcpy(name, hostname, len);
    name[len] = 0;
    cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
    *ip_addr = name;
    return 0;
}