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
dns_resolve_server_name_to_ip(const char * unc,char ** ip_addr)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 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
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 }
99