fs/cifs/dns_resolve.c

   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  */
  45 int
  46 dns_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                 cERROR(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
  89 name_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 }