linux/fs/cifs/dns_resolve.c
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   1/*
   2 *  fs/cifs/dns_resolve.c
   3 *
   4 *   Copyright (c) 2007 Igor Mammedov
   5 *   Author(s): Igor Mammedov (niallain@gmail.com)
   6 *              Steve French (sfrench@us.ibm.com)
   7 *              Wang Lei (wang840925@gmail.com)
   8 *              David Howells (dhowells@redhat.com)
   9 *
  10 *   Contains the CIFS DFS upcall routines used for hostname to
  11 *   IP address translation.
  12 *
  13 *   This library is free software; you can redistribute it and/or modify
  14 *   it under the terms of the GNU Lesser General Public License as published
  15 *   by the Free Software Foundation; either version 2.1 of the License, or
  16 *   (at your option) any later version.
  17 *
  18 *   This library is distributed in the hope that it will be useful,
  19 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  20 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
  21 *   the GNU Lesser General Public License for more details.
  22 *
  23 *   You should have received a copy of the GNU Lesser General Public License
  24 *   along with this library; if not, write to the Free Software
  25 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  26 */
  27
  28#include <linux/slab.h>
  29#include <linux/dns_resolver.h>
  30#include "dns_resolve.h"
  31#include "cifsglob.h"
  32#include "cifsproto.h"
  33#include "cifs_debug.h"
  34
  35/**
  36 * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
  37 * @unc: UNC path specifying the server
  38 * @ip_addr: Where to return the IP address.
  39 *
  40 * The IP address will be returned in string form, and the caller is
  41 * responsible for freeing it.
  42 *
  43 * Returns length of result on success, -ve on error.
  44 */
  45int
  46dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
  47{
  48        struct sockaddr_storage ss;
  49        const char *hostname, *sep;
  50        char *name;
  51        int len, rc;
  52
  53        if (!ip_addr || !unc)
  54                return -EINVAL;
  55
  56        len = strlen(unc);
  57        if (len < 3) {
  58                cFYI(1, "%s: unc is too short: %s", __func__, unc);
  59                return -EINVAL;
  60        }
  61
  62        /* Discount leading slashes for cifs */
  63        len -= 2;
  64        hostname = unc + 2;
  65
  66        /* Search for server name delimiter */
  67        sep = memchr(hostname, '\\', len);
  68        if (sep)
  69                len = sep - hostname;
  70        else
  71                cFYI(1, "%s: probably server name is whole unc: %s",
  72                     __func__, unc);
  73
  74        /* Try to interpret hostname as an IPv4 or IPv6 address */
  75        rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
  76        if (rc > 0)
  77                goto name_is_IP_address;
  78
  79        /* Perform the upcall */
  80        rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
  81        if (rc < 0)
  82                cFYI(1, "%s: unable to resolve: %*.*s",
  83                        __func__, len, len, hostname);
  84        else
  85                cFYI(1, "%s: resolved: %*.*s to %s",
  86                     __func__, len, len, hostname, *ip_addr);
  87        return rc;
  88
  89name_is_IP_address:
  90        name = kmalloc(len + 1, GFP_KERNEL);
  91        if (!name)
  92                return -ENOMEM;
  93        memcpy(name, hostname, len);
  94        name[len] = 0;
  95        cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
  96        *ip_addr = name;
  97        return 0;
  98}
  99
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