cifs-utils/SOURCES/Implement-CLDAP-Ping-to-find-the-closest-site.patch

From 770e891a8b7ad53d4d700e08cf8d3154028b4588 Mon Sep 17 00:00:00 2001
From: David Voit <david.voit@gmail.com>
Date: Wed, 3 Apr 2024 07:24:48 +0200
Subject: [PATCH] Implement CLDAP Ping to find the closest site

For domain based DFS we always need to contact the domain controllers.
On setups, which are using bigger AD installations you could get random dc on the other side of the world,
if you don't have site support. This can lead to network timeouts and other problems.

CLDAP-Ping uses ASN.1 + UDP (CLDAP) and custom-DCE encoding including DName compressions without
field separation. Finally after finding the sitename we now need to do a DNS SRV lookups to find
the correct IPs to our closest site and fill up the remaining IPs from the global list.

Signed-off-by: David Voit <david.voit@gmail.com>
---
 Makefile.am    |  15 ++-
 cldap_ping.c   | 345 +++++++++++++++++++++++++++++++++++++++++++++++++
 cldap_ping.h   |  14 ++
 mount.cifs.c   |   5 +-
 resolve_host.c | 256 ++++++++++++++++++++++++++++++++----
 resolve_host.h |   6 +-
 6 files changed, 604 insertions(+), 37 deletions(-)
 create mode 100644 cldap_ping.c
 create mode 100644 cldap_ping.h

Index: cifs-utils/Makefile.am
===================================================================
--- cifs-utils.orig/Makefile.am
+++ cifs-utils/Makefile.am
@@ -3,8 +3,8 @@ ACLOCAL_AMFLAGS = -I aclocal
 
 root_sbindir = $(ROOTSBINDIR)
 root_sbin_PROGRAMS = mount.cifs
-mount_cifs_SOURCES = mount.cifs.c mtab.c resolve_host.c util.c
-mount_cifs_LDADD = $(LIBCAP) $(CAPNG_LDADD) $(RT_LDADD)
+mount_cifs_SOURCES = mount.cifs.c mtab.c $(resolve_hosts_SOURCES) util.c
+mount_cifs_LDADD = $(LIBCAP) $(CAPNG_LDADD) $(RT_LDADD) $(resolve_hosts_LDADD)
 include_HEADERS = cifsidmap.h
 rst_man_pages = mount.cifs.8
 
@@ -28,6 +28,9 @@ bin_PROGRAMS =
 bin_SCRIPTS =
 sbin_PROGRAMS =
 
+resolve_hosts_SOURCES = data_blob.c asn1.c cldap_ping.c resolve_host.c
+resolve_hosts_LDADD = -ltalloc -lresolv
+
 if CONFIG_CIFSUPCALL
 sbin_PROGRAMS += cifs.upcall
 cifs_upcall_SOURCES = cifs.upcall.c data_blob.c asn1.c spnego.c
@@ -43,8 +46,8 @@ endif
 
 if CONFIG_CIFSCREDS
 bin_PROGRAMS += cifscreds
-cifscreds_SOURCES = cifscreds.c cifskey.c resolve_host.c util.c
-cifscreds_LDADD = -lkeyutils
+cifscreds_SOURCES = cifscreds.c cifskey.c $(resolve_hosts_SOURCES) util.c
+cifscreds_LDADD = -lkeyutils $(resolve_hosts_LDADD)
 
 rst_man_pages += cifscreds.1
 
@@ -105,8 +108,8 @@ endif
 if CONFIG_PAM
 pam_PROGRAMS = pam_cifscreds.so
 rst_man_pages += pam_cifscreds.8
-pam_cifscreds.so: pam_cifscreds.c cifskey.c resolve_host.c util.c
-	$(CC) $(DEFS) $(CFLAGS) $(AM_CFLAGS) $(LDFLAGS) -shared -fpic -o $@ $+ -lpam -lkeyutils
+pam_cifscreds.so: pam_cifscreds.c cifskey.c $(resolve_hosts_SOURCES) util.c
+	$(CC) $(DEFS) $(CFLAGS) $(AM_CFLAGS) $(LDFLAGS) -shared -fpic -o $@ $+ -lpam -lkeyutils $(resolve_hosts_LDADD)
 
 endif
 
Index: cifs-utils/cldap_ping.c
===================================================================
--- /dev/null
+++ cifs-utils/cldap_ping.c
@@ -0,0 +1,345 @@
+/*
+ * CLDAP Ping to find closest ClientSiteName
+ *
+ * Copyright (C) 2024 David Voit (david.voit@gmail.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <talloc.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include <resolv.h>
+#include <stdbool.h>
+#include "data_blob.h"
+#include "asn1.h"
+#include "cldap_ping.h"
+
+#define LDAP_DNS_DOMAIN "DnsDomain"
+#define LDAP_DNS_DOMAIN_LEN strlen(LDAP_DNS_DOMAIN)
+#define LDAP_NT_VERSION "NtVer"
+#define LDAP_NT_VERSION_LEN strlen(LDAP_NT_VERSION)
+#define LDAP_ATTRIBUTE_NETLOGON "NetLogon"
+#define LDAP_ATTRIBUTE_NETLOGON_LEN strlen(LDAP_ATTRIBUTE_NETLOGON)
+
+
+// Parse a ASN.1 BER tag size-field, returns start of payload of tag
+char *parse_ber_size(char *buf, size_t *tag_size) {
+	size_t size = *buf & 0xff;
+	char *ret = (buf + 1);
+	if (size >= 0x81) {
+		switch (size) {
+			case 0x81:
+				size = *ret & 0xff;
+				ret += 1;
+				break;
+			case 0x82:
+				size = (*ret << 8) | (*(ret + 1) & 0xff);
+				ret += 2;
+				break;
+			case 0x83:
+				size = (*ret << 16) | (*(ret + 1) << 8) | (*(ret + 2) & 0xff);
+				ret += 3;
+				break;
+			case 0x84:
+				size = (*ret << 24) | (*(ret + 1) << 16) | (*(ret + 2) << 8) | (*(ret + 3) & 0xff);
+				ret += 4;
+				break;
+			default:
+				return NULL;
+		}
+	}
+
+	*tag_size = size;
+	return ret;
+}
+
+// simple wrapper over dn_expand which also calculates the new offset for the next compressed dn
+int read_dns_string(char *buf, size_t buf_size, char *dest, size_t dest_size, size_t *offset) {
+	int compressed_length = dn_expand((u_char *)buf, (u_char *)buf+buf_size, (u_char *)buf + *offset, dest, (int)dest_size);
+	if (compressed_length < 0) {
+		return -1;
+	}
+
+	*offset = *offset+compressed_length;
+
+	return 0;
+}
+
+// LDAP request for: (&(DnsDomain=DOMAIN_HERE)(NtVer=\\06\\00\\00\\00))
+ASN1_DATA *generate_cldap_query(char *domain) {
+	ASN1_DATA *data;
+	TALLOC_CTX *mem_ctx = talloc_init("cldap");
+
+	data = asn1_init(mem_ctx);
+	asn1_push_tag(data, ASN1_SEQUENCE(0));
+
+	// Message id
+	asn1_push_tag(data, ASN1_INTEGER);
+	asn1_write_uint8(data, 1);
+	asn1_pop_tag(data);
+
+	// SearchRequest
+	asn1_push_tag(data, ASN1_APPLICATION(3));
+
+	// empty baseObject
+	asn1_push_tag(data, ASN1_OCTET_STRING);
+	asn1_pop_tag(data);
+
+	// scope 0 = baseObject
+	asn1_push_tag(data, ASN1_ENUMERATED);
+	asn1_write_uint8(data, 0);
+	asn1_pop_tag(data);
+
+	// derefAliasses 0=neverDerefAlias
+	asn1_push_tag(data, ASN1_ENUMERATED);
+	asn1_write_uint8(data, 0);
+	asn1_pop_tag(data);
+
+	// sizeLimit
+	asn1_push_tag(data, ASN1_INTEGER);
+	asn1_write_uint8(data, 0);
+	asn1_pop_tag(data);
+
+	// timeLimit
+	asn1_push_tag(data, ASN1_INTEGER);
+	asn1_write_uint8(data, 0);
+	asn1_pop_tag(data);
+
+	// typesOnly
+	asn1_push_tag(data, ASN1_BOOLEAN);
+	asn1_write_uint8(data, 0);
+	asn1_pop_tag(data);
+
+	// AND
+	asn1_push_tag(data, ASN1_CONTEXT(0));
+	// equalityMatch
+	asn1_push_tag(data, ASN1_CONTEXT(3));
+	asn1_write_OctetString(data, LDAP_DNS_DOMAIN, LDAP_DNS_DOMAIN_LEN);
+	asn1_write_OctetString(data, domain, strlen(domain));
+	asn1_pop_tag(data);
+
+	// equalityMatch
+	asn1_push_tag(data, ASN1_CONTEXT(3));
+	asn1_write_OctetString(data, LDAP_NT_VERSION, LDAP_NT_VERSION_LEN);
+	// Bitmask NETLOGON_NT_VERSION_5 & NETLOGON_NT_VERSION_5EX -> To get NETLOGON_SAM_LOGON_RESPONSE_EX as response
+	asn1_write_OctetString(data, "\x06\x00\x00\x00", 4);
+	asn1_pop_tag(data);
+
+	// End AND
+	asn1_pop_tag(data);
+
+	asn1_push_tag(data, ASN1_SEQUENCE(0));
+	asn1_write_OctetString(data, LDAP_ATTRIBUTE_NETLOGON, LDAP_ATTRIBUTE_NETLOGON_LEN);
+	asn1_pop_tag(data);
+
+	// End SearchRequest
+	asn1_pop_tag(data);
+	// End Sequence
+	asn1_pop_tag(data);
+
+	return data;
+}
+
+// Input is a cldap response, output is a pointer to the NETLOGON_SAM_LOGON_RESPONSE_EX payload
+ssize_t extract_netlogon_section(char *buffer, size_t buffer_size, char **netlogon_payload) {
+	size_t ber_size;
+	size_t netlogon_payload_size;
+	// Not enough space to read initial sequence - not an correct cldap response
+	if (buffer_size < 7) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	// Sequence tag
+	if (*buffer != 0x30) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *message_id_tag = parse_ber_size(buffer + 1, &ber_size);
+
+	if (ber_size > buffer_size) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	if (*message_id_tag != 0x02) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *message_id = parse_ber_size(message_id_tag + 1, &ber_size);
+
+	if (ber_size != 1 || *message_id != 1) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	// SearchResultEntry
+	if (*(message_id+1) != 0x64) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *object_name_tag = parse_ber_size(message_id+2, &ber_size);
+	if (object_name_tag == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *object_name = parse_ber_size(object_name_tag+1, &ber_size);
+	if (object_name == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	if (*object_name_tag != 4 || ber_size != 0) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *partial_attribute_list_tag = parse_ber_size(object_name+1, &ber_size);
+	if (partial_attribute_list_tag == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	if (*partial_attribute_list_tag != 0x30) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+
+	char *partial_attribute_tag = parse_ber_size(partial_attribute_list_tag+1, &ber_size);
+	if (partial_attribute_tag == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *attribute_name = parse_ber_size(partial_attribute_tag+1, &ber_size);
+	if (attribute_name == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	if (ber_size != LDAP_ATTRIBUTE_NETLOGON_LEN) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	if (strncasecmp(LDAP_ATTRIBUTE_NETLOGON, attribute_name, LDAP_ATTRIBUTE_NETLOGON_LEN) != 0) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	// SET
+	if (*(attribute_name+LDAP_ATTRIBUTE_NETLOGON_LEN) != 0x31) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	char *start_of_data = parse_ber_size(attribute_name+LDAP_ATTRIBUTE_NETLOGON_LEN+1, &ber_size);
+	if (start_of_data == NULL) {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	// octat-string of NetLogon data
+	if (*start_of_data != '\x04') {
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	*netlogon_payload = parse_ber_size(start_of_data + 1, &netlogon_payload_size);
+
+	if (*netlogon_payload == NULL) {
+		*netlogon_payload = NULL;
+		return CLDAP_PING_PARSE_ERROR_LDAP;
+	}
+
+	return (ssize_t)netlogon_payload_size;
+}
+
+int netlogon_get_client_site(char *netlogon_response, size_t netlogon_size, char *sitename) {
+	// 24 mandatory bytes
+	if (netlogon_size < 25) {
+		return CLDAP_PING_PARSE_ERROR_NETLOGON;
+	}
+
+	// LOGON_SAM_PAUSE_RESPONSE_EX -> Netlogon service is not in-sync try next dc instead
+	if (*netlogon_response == 0x18 && *(netlogon_response + 1) == 0x00) {
+		return CLDAP_PING_TRYNEXT;
+	}
+
+	// NETLOGON_SAM_LOGON_RESPONSE_EX Opcode: 0x17
+	if (*netlogon_response != 0x17 || *(netlogon_response + 1) != 0x00) {
+		return CLDAP_PING_PARSE_ERROR_NETLOGON;
+	}
+
+	// skip over sbz, ds_flags and domain_guid
+	// and start directly at variable string portion of NETLOGON_SAM_LOGON_RESPONSE_EX
+	size_t offset = 24;
+
+	for (int i=0; i < 8; i++) {
+		// iterate over DnsForestName, DnsDomainName, NetbiosDomainName, NetbiosComputerName, UserName, DcSiteName
+		// to finally get to our desired ClientSiteName field
+		if (read_dns_string(netlogon_response, netlogon_size, sitename, MAXCDNAME, &offset) < 0) {
+			return CLDAP_PING_PARSE_ERROR_NETLOGON;
+		}
+	}
+
+	return 0;
+}
+
+int cldap_ping(char *domain, sa_family_t family, void *addr, char *site_name) {
+	char buffer[8196];
+	ssize_t response_size;
+	char *netlogon_response;
+	ssize_t netlogon_size;
+	struct sockaddr_storage socketaddr;
+	size_t addr_size;
+	int sock = socket(family, SOCK_DGRAM, 0);
+	if (sock < 0) {
+		return CLDAP_PING_NETWORK_ERROR;
+	}
+
+	ASN1_DATA *data = generate_cldap_query(domain);
+
+	if (family == AF_INET6) {
+		addr_size = sizeof(struct sockaddr_in6);
+		bzero((void *) &socketaddr, addr_size);
+		socketaddr.ss_family = AF_INET6;
+		((struct sockaddr_in6 *)&socketaddr)->sin6_addr = *((struct in6_addr*)addr);
+		((struct sockaddr_in6 *)&socketaddr)->sin6_port = htons(389);
+	} else {
+		addr_size = sizeof(struct sockaddr_in);
+		bzero((void *) &socketaddr, addr_size);
+		socketaddr.ss_family = AF_INET;
+		((struct sockaddr_in *)&socketaddr)->sin_addr = *((struct in_addr*)addr);
+		((struct sockaddr_in *)&socketaddr)->sin_port = htons(389);
+	}
+
+	struct timeval timeout = {.tv_sec = 2, .tv_usec = 0};
+	if (setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof(timeout)) < 0) {
+		return CLDAP_PING_NETWORK_ERROR;
+	}
+	if (setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
+		return CLDAP_PING_NETWORK_ERROR;
+	}
+
+	if (sendto(sock, data->data, data->length, 0, (struct sockaddr *)&socketaddr, addr_size) < 0) {
+		close(sock);
+		return CLDAP_PING_TRYNEXT;
+	}
+
+	asn1_free(data);
+	response_size = recv(sock, buffer, sizeof(buffer), 0);
+	close(sock);
+
+	if (response_size < 0) {
+		return CLDAP_PING_TRYNEXT;
+	}
+
+	netlogon_size = extract_netlogon_section(buffer, response_size, &netlogon_response);
+	if (netlogon_size < 0) {
+		return (int)netlogon_size;
+	}
+
+	return netlogon_get_client_site(netlogon_response, netlogon_size, site_name);
+}
Index: cifs-utils/cldap_ping.h
===================================================================
--- /dev/null
+++ cifs-utils/cldap_ping.h
@@ -0,0 +1,14 @@
+#ifndef _CLDAP_PING_H_
+#define _CLDAP_PING_H_
+
+#define CLDAP_PING_NETWORK_ERROR -1
+#define CLDAP_PING_TRYNEXT -2
+#define CLDAP_PING_PARSE_ERROR_LDAP -3
+#define CLDAP_PING_PARSE_ERROR_NETLOGON -4
+
+// returns CLDAP_PING_TRYNEXT if you should use another dc
+// any other error code < 0 is a fatal error
+// site_name must be of MAXCDNAME size!
+int cldap_ping(char *domain, sa_family_t family, void *addr, char *site_name);
+
+#endif /* _CLDAP_PING_H_ */
Index: cifs-utils/mount.cifs.c
===================================================================
--- cifs-utils.orig/mount.cifs.c
+++ cifs-utils/mount.cifs.c
@@ -1889,8 +1889,11 @@ assemble_mountinfo(struct parsed_mount_i
 	if (rc)
 		goto assemble_exit;
 
-	if (parsed_info->addrlist[0] == '\0')
+	if (parsed_info->addrlist[0] == '\0') {
 		rc = resolve_host(parsed_info->host, parsed_info->addrlist);
+		if (rc == 0 && parsed_info->verboseflag)
+			fprintf(stderr, "Host \"%s\" resolved to the following IP addresses: %s\n", parsed_info->host, parsed_info->addrlist);
+	}
 
 	switch (rc) {
 	case EX_USAGE:
Index: cifs-utils/resolve_host.c
===================================================================
--- cifs-utils.orig/resolve_host.c
+++ cifs-utils/resolve_host.c
@@ -3,6 +3,7 @@
  *
  * Copyright (C) 2010 Jeff Layton (jlayton@samba.org)
  * Copyright (C) 2010 Igor Druzhinin (jaxbrigs@gmail.com)
+ * Copyright (C) 2024 David Voit (david.voit@gmail.com)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -27,15 +28,16 @@
 #include <sys/socket.h>
 #include <arpa/inet.h>
 #include <netdb.h>
+#include <resolv.h>
 #include "mount.h"
 #include "util.h"
+#include "cldap_ping.h"
 #include "resolve_host.h"
 
 /*
  * resolve hostname to comma-separated list of address(es)
  */
-int resolve_host(const char *host, char *addrstr)
-{
+int resolve_host(const char *host, char *addrstr) {
 	int rc;
 	/* 10 for max width of decimal scopeid */
 	char tmpbuf[NI_MAXHOST + 1 + 10 + 1];
@@ -44,6 +46,7 @@ int resolve_host(const char *host, char
 	struct addrinfo *addrlist, *addr;
 	struct sockaddr_in *sin;
 	struct sockaddr_in6 *sin6;
+	size_t count_v4 = 0, count_v6 = 0;
 
 	rc = getaddrinfo(host, NULL, NULL, &addrlist);
 	if (rc != 0)
@@ -59,34 +62,45 @@ int resolve_host(const char *host, char
 		}
 
 		switch (addr->ai_addr->sa_family) {
-		case AF_INET6:
-			sin6 = (struct sockaddr_in6 *)addr->ai_addr;
-			ipaddr = inet_ntop(AF_INET6, &sin6->sin6_addr, tmpbuf,
-					   sizeof(tmpbuf));
-			if (!ipaddr) {
-				rc = EX_SYSERR;
-				goto resolve_host_out;
-			}
-
-			if (sin6->sin6_scope_id) {
-				len = strnlen(tmpbuf, sizeof(tmpbuf));
-				snprintf(tmpbuf + len, sizeof(tmpbuf) - len, "%%%u",
-					 sin6->sin6_scope_id);
-			}
-			break;
-		case AF_INET:
-			sin = (struct sockaddr_in *)addr->ai_addr;
-			ipaddr = inet_ntop(AF_INET, &sin->sin_addr, tmpbuf,
-					   sizeof(tmpbuf));
-			if (!ipaddr) {
-				rc = EX_SYSERR;
-				goto resolve_host_out;
-			}
-
-			break;
-		default:
-			addr = addr->ai_next;
-			continue;
+			case AF_INET6:
+				count_v6++;
+				if (count_v6 + count_v4 > MAX_ADDRESSES) {
+					addr = addr->ai_next;
+					continue;
+				}
+
+				sin6 = (struct sockaddr_in6 *) addr->ai_addr;
+				ipaddr = inet_ntop(AF_INET6, &sin6->sin6_addr, tmpbuf,
+								   sizeof(tmpbuf));
+				if (!ipaddr) {
+					rc = EX_SYSERR;
+					goto resolve_host_out;
+				}
+
+
+				if (sin6->sin6_scope_id) {
+					len = strnlen(tmpbuf, sizeof(tmpbuf));
+					snprintf(tmpbuf + len, sizeof(tmpbuf) - len, "%%%u",
+							 sin6->sin6_scope_id);
+				}
+				break;
+			case AF_INET:
+				count_v4++;
+				if (count_v6 + count_v4 > MAX_ADDRESSES) {
+					addr = addr->ai_next;
+					continue;
+				}
+				sin = (struct sockaddr_in *) addr->ai_addr;
+				ipaddr = inet_ntop(AF_INET, &sin->sin_addr, tmpbuf,
+								   sizeof(tmpbuf));
+				if (!ipaddr) {
+					rc = EX_SYSERR;
+					goto resolve_host_out;
+				}
+				break;
+			default:
+				addr = addr->ai_next;
+				continue;
 		}
 
 		if (addr == addrlist)
@@ -98,6 +112,192 @@ int resolve_host(const char *host, char
 		addr = addr->ai_next;
 	}
 
+
+	// Is this a DFS domain where we need to do a cldap ping to find the closest node?
+	if (count_v4 > 1 || count_v6 > 1) {
+		int res;
+		ns_msg global_domain_handle;
+		unsigned char global_domain_lookup[4096];
+		ns_msg site_domain_handle;
+		unsigned char site_domain_lookup[4096];
+		char dname[MAXCDNAME];
+		int srv_cnt;
+
+		res = res_init();
+		if (res != 0)
+			goto resolve_host_out;
+
+		res = snprintf(dname, MAXCDNAME, "_ldap._tcp.dc._msdcs.%s", host);
+		if (res < 0)
+			goto resolve_host_out;
+
+		res = res_query(dname, C_IN, ns_t_srv, global_domain_lookup, sizeof(global_domain_lookup));
+		if (res < 0)
+			goto resolve_host_out;
+
+		// res is also the size of the response_buffer
+		res = ns_initparse(global_domain_lookup, res, &global_domain_handle);
+		if (res < 0)
+			goto resolve_host_out;
+
+		srv_cnt = ns_msg_count (global_domain_handle, ns_s_an);
+
+		// No or just one DC we are done
+		if (srv_cnt < 2)
+			goto resolve_host_out;
+
+		char site_name[MAXCDNAME];
+		// We assume that AD always sends the ip addresses in the addtional data block
+		for (int i = 0; i < ns_msg_count(global_domain_handle, ns_s_ar); i++) {
+			ns_rr rr;
+			res = ns_parserr(&global_domain_handle, ns_s_ar, i, &rr);
+			if (res < 0)
+				goto resolve_host_out;
+
+			switch (ns_rr_type(rr)) {
+				case ns_t_aaaa:
+					if (ns_rr_rdlen(rr) != NS_IN6ADDRSZ)
+						continue;
+					res = cldap_ping((char *) host, AF_INET6, (void *)ns_rr_rdata(rr), site_name);
+					break;
+				case ns_t_a:
+					if (ns_rr_rdlen(rr) != NS_INADDRSZ)
+						continue;
+					res = cldap_ping((char *) host, AF_INET, (void *)ns_rr_rdata(rr), site_name);
+					break;
+				default:
+					continue;
+			}
+
+			if (res == CLDAP_PING_TRYNEXT) {
+				continue;
+			}
+
+			if (res < 0) {
+				goto resolve_host_out;
+			}
+
+			if (site_name[0] == '\0') {
+				goto resolve_host_out;
+			} else {
+				// site found - leave loop
+				break;
+			}
+		}
+
+		res = snprintf(dname, MAXCDNAME, "_ldap._tcp.%s._sites.dc._msdcs.%s", site_name, host);
+		if (res < 0) {
+			goto resolve_host_out;
+		}
+
+		res = res_query(dname, C_IN, ns_t_srv, site_domain_lookup, sizeof(site_domain_lookup));
+		if (res < 0)
+			goto resolve_host_out;
+
+		// res is also the size of the response_buffer
+		res = ns_initparse(site_domain_lookup, res, &site_domain_handle);
+		if (res < 0)
+			goto resolve_host_out;
+
+		int number_addresses = 0;
+		for (int i = 0; i < ns_msg_count(site_domain_handle, ns_s_ar); i++) {
+			if (i > MAX_ADDRESSES)
+				break;
+
+			ns_rr rr;
+			res = ns_parserr(&site_domain_handle, ns_s_ar, i, &rr);
+			if (res < 0)
+				goto resolve_host_out;
+
+			switch (ns_rr_type(rr)) {
+				case ns_t_aaaa:
+					if (ns_rr_rdlen(rr) != NS_IN6ADDRSZ)
+						continue;
+					ipaddr = inet_ntop(AF_INET6, ns_rr_rdata(rr), tmpbuf,
+									   sizeof(tmpbuf));
+					if (!ipaddr) {
+						rc = EX_SYSERR;
+						goto resolve_host_out;
+					}
+					break;
+				case ns_t_a:
+					if (ns_rr_rdlen(rr) != NS_INADDRSZ)
+						continue;
+					ipaddr = inet_ntop(AF_INET, ns_rr_rdata(rr), tmpbuf,
+									   sizeof(tmpbuf));
+					if (!ipaddr) {
+						rc = EX_SYSERR;
+						goto resolve_host_out;
+					}
+					break;
+				default:
+					continue;
+			}
+
+			number_addresses++;
+
+			if (i == 0)
+				*addrstr = '\0';
+			else
+				strlcat(addrstr, ",", MAX_ADDR_LIST_LEN);
+
+			strlcat(addrstr, tmpbuf, MAX_ADDR_LIST_LEN);
+		}
+
+		// Preferred site ips is now the first entry in addrstr, fill up with other sites till MAX_ADDRESS
+		for (int i = 0; i < ns_msg_count(global_domain_handle, ns_s_ar); i++) {
+			if (number_addresses > MAX_ADDRESSES)
+				break;
+
+			ns_rr rr;
+			res = ns_parserr(&global_domain_handle, ns_s_ar, i, &rr);
+			if (res < 0)
+				goto resolve_host_out;
+
+			switch (ns_rr_type(rr)) {
+				case ns_t_aaaa:
+					if (ns_rr_rdlen(rr) != NS_IN6ADDRSZ)
+						continue;
+					ipaddr = inet_ntop(AF_INET6, ns_rr_rdata(rr), tmpbuf,
+									   sizeof(tmpbuf));
+					if (!ipaddr) {
+						rc = EX_SYSERR;
+						goto resolve_host_out;
+					}
+					break;
+				case ns_t_a:
+					if (ns_rr_rdlen(rr) != NS_INADDRSZ)
+						continue;
+					ipaddr = inet_ntop(AF_INET, ns_rr_rdata(rr), tmpbuf,
+									   sizeof(tmpbuf));
+					if (!ipaddr) {
+						rc = EX_SYSERR;
+						goto resolve_host_out;
+					}
+					break;
+				default:
+					continue;
+			}
+
+			char *found = strstr(addrstr, tmpbuf);
+
+			if (found) {
+				// We only have a real match if the substring is between  ',' or it's the last/first entry in the list
+				char previous_seperator = found > addrstr ? *(found-1) : '\0';
+				char next_seperator = *(found+strlen(tmpbuf));
+
+				if ((next_seperator == ',' || next_seperator == '\0')
+					&& (previous_seperator == ',' || previous_seperator == '\0')) {
+					continue;
+				}
+			}
+
+			number_addresses++;
+			strlcat(addrstr, ",", MAX_ADDR_LIST_LEN);
+			strlcat(addrstr, tmpbuf, MAX_ADDR_LIST_LEN);
+		}
+	}
+
 resolve_host_out:
 	freeaddrinfo(addrlist);
 	return rc;
Index: cifs-utils/resolve_host.h
===================================================================
--- cifs-utils.orig/resolve_host.h
+++ cifs-utils/resolve_host.h
@@ -26,8 +26,10 @@
 /* currently maximum length of IPv6 address string */
 #define MAX_ADDRESS_LEN INET6_ADDRSTRLEN
 
-/* limit list of addresses to 16 max-size addrs */
-#define MAX_ADDR_LIST_LEN ((MAX_ADDRESS_LEN + 1) * 16)
+#define MAX_ADDRESSES 16
+
+/* limit list of addresses to MAX_ADDRESSES max-size addrs */
+#define MAX_ADDR_LIST_LEN ((MAX_ADDRESS_LEN + 1) * MAX_ADDRESSES)
 
 extern int resolve_host(const char *host, char *addrstr);