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 */
31 int
32 dns_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
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