1// SPDX-License-Identifier: LGPL-2.1
 2/*
 3 *  fs/cifs/dns_resolve.c
 4 *
 5 *   Copyright (c) 2007 Igor Mammedov
 6 *   Author(s): Igor Mammedov (niallain@gmail.com)
 7 *              Steve French (sfrench@us.ibm.com)
 8 *              Wang Lei (wang840925@gmail.com)
 9 *		David Howells (dhowells@redhat.com)
10 *
11 *   Contains the CIFS DFS upcall routines used for hostname to
12 *   IP address translation.
13 *
14 */
15
16#include <linux/slab.h>
17#include <linux/dns_resolver.h>
18#include "dns_resolve.h"
19#include "cifsglob.h"
20#include "cifsproto.h"
21#include "cifs_debug.h"
22
23/**
24 * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
25 * @unc: UNC path specifying the server (with '/' as delimiter)
26 * @ip_addr: Where to return the IP address.
27 * @expiry: Where to return the expiry time for the dns record.
28 *
29 * The IP address will be returned in string form, and the caller is
30 * responsible for freeing it.
31 *
32 * Returns length of result on success, -ve on error.
33 */
34int
35dns_resolve_server_name_to_ip(const char *unc, char **ip_addr, time64_t *expiry)
36{
37	struct sockaddr_storage ss;
38	const char *hostname, *sep;
39	char *name;
40	int len, rc;
41
42	if (!ip_addr || !unc)
43		return -EINVAL;
44
45	len = strlen(unc);
46	if (len < 3) {
47		cifs_dbg(FYI, "%s: unc is too short: %s\n", __func__, unc);
48		return -EINVAL;
49	}
50
51	/* Discount leading slashes for cifs */
52	len -= 2;
53	hostname = unc + 2;
54
55	/* Search for server name delimiter */
56	sep = memchr(hostname, '/', len);
57	if (sep)
58		len = sep - hostname;
59	else
60		cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
61			 __func__, unc);
62
63	/* Try to interpret hostname as an IPv4 or IPv6 address */
64	rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
65	if (rc > 0)
66		goto name_is_IP_address;
67
68	/* Perform the upcall */
69	rc = dns_query(current->nsproxy->net_ns, NULL, hostname, len,
70		       NULL, ip_addr, expiry, false);
71	if (rc < 0)
72		cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
73			 __func__, len, len, hostname);
74	else
75		cifs_dbg(FYI, "%s: resolved: %*.*s to %s expiry %llu\n",
76			 __func__, len, len, hostname, *ip_addr,
77			 expiry ? (*expiry) : 0);
78	return rc;
79
80name_is_IP_address:
81	name = kmalloc(len + 1, GFP_KERNEL);
82	if (!name)
83		return -ENOMEM;
84	memcpy(name, hostname, len);
85	name[len] = 0;
86	cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s\n",
87		 __func__, name);
88	*ip_addr = name;
89	return 0;
90}