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
dns_resolve_server_name_to_ip(const char * unc,struct sockaddr * ip_addr,time64_t * expiry)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