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/inet.h>
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 * Returns zero success, -ve on error.
30 */
31int
32dns_resolve_server_name_to_ip(const char *unc, struct sockaddr *ip_addr, time64_t *expiry)
33{
34	const char *hostname, *sep;
35	char *ip;
36	int len, rc;
37
38	if (!ip_addr || !unc)
39		return -EINVAL;
40
41	len = strlen(unc);
42	if (len < 3) {
43		cifs_dbg(FYI, "%s: unc is too short: %s\n", __func__, unc);
44		return -EINVAL;
45	}
46
47	/* Discount leading slashes for cifs */
48	len -= 2;
49	hostname = unc + 2;
50
51	/* Search for server name delimiter */
52	sep = memchr(hostname, '/', len);
53	if (sep)
54		len = sep - hostname;
55	else
56		cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
57			 __func__, unc);
58
59	/* Try to interpret hostname as an IPv4 or IPv6 address */
60	rc = cifs_convert_address(ip_addr, hostname, len);
61	if (rc > 0) {
62		cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %*.*s\n", __func__, len, len,
63			 hostname);
64		return 0;
65	}
66
67	/* Perform the upcall */
68	rc = dns_query(current->nsproxy->net_ns, NULL, hostname, len,
69		       NULL, &ip, 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,
76			 expiry ? (*expiry) : 0);
77
78		rc = cifs_convert_address(ip_addr, ip, strlen(ip));
79		kfree(ip);
80
81		if (!rc) {
82			cifs_dbg(FYI, "%s: unable to determine ip address\n", __func__);
83			rc = -EHOSTUNREACH;
84		} else
85			rc = 0;
86	}
87	return rc;
88}
89