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		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
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