fs/cifs/dns_resolve.c

   1 // SPDX-License-Identifier: LGPL-2.1
   2 /*
   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  */
  14
  15 #include <linux/slab.h>
  16 #include <linux/dns_resolver.h>
  17 #include "dns_resolve.h"
  18 #include "cifsglob.h"
  19 #include "cifsproto.h"
  20 #include "cifs_debug.h"
  21
  22 /**
  23  * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
  24  * @unc: UNC path specifying the server (with '/' as delimiter)
  25  * @ip_addr: Where to return the IP address.
  26  * @expiry: Where to return the expiry time for the dns record.
  27  *
  28  * The IP address will be returned in string form, and the caller is
  29  * responsible for freeing it.
  30  *
  31  * Returns length of result on success, -ve on error.
  32  */
  33 int
  34 dns_resolve_server_name_to_ip(const char *unc, char **ip_addr, time64_t *expiry)
  35 {
  36         struct sockaddr_storage ss;
  37         const char *hostname, *sep;
  38         char *name;
  39         int len, rc;
  40
  41         if (!ip_addr || !unc)
  42                 return -EINVAL;
  43
  44         len = strlen(unc);
  45         if (len < 3) {
  46                 cifs_dbg(FYI, "%s: unc is too short: %s\n", __func__, unc);
  47                 return -EINVAL;
  48         }
  49
  50         /* Discount leading slashes for cifs */
  51         len -= 2;
  52         hostname = unc + 2;
  53
  54         /* Search for server name delimiter */
  55         sep = memchr(hostname, '/', len);
  56         if (sep)
  57                 len = sep - hostname;
  58         else
  59                 cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
  60                          __func__, unc);
  61
  62         /* Try to interpret hostname as an IPv4 or IPv6 address */
  63         rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
  64         if (rc > 0)
  65                 goto name_is_IP_address;
  66
  67         /* Perform the upcall */
  68         rc = dns_query(current->nsproxy->net_ns, NULL, hostname, len,
  69                        NULL, ip_addr, expiry, false);
  70         if (rc < 0)
  71                 cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
  72                          __func__, len, len, hostname);
  73         else
  74                 cifs_dbg(FYI, "%s: resolved: %*.*s to %s expiry %llu\n",
  75                          __func__, len, len, hostname, *ip_addr,
  76                          expiry ? (*expiry) : 0);
  77         return rc;
  78
  79 name_is_IP_address:
  80         name = kmalloc(len + 1, GFP_KERNEL);
  81         if (!name)
  82                 return -ENOMEM;
  83         memcpy(name, hostname, len);
  84         name[len] = 0;
  85         cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s\n",
  86                  __func__, name);
  87         *ip_addr = name;
  88         return 0;
  89 }