cc706b50b9
If AES-128-GCM-SIV is available on the client, add it to the requested algorithms in NTS-KE as the first (preferred) entry. If supported on the server, it will make the cookies shorter, which will get the length of NTP messages containing only one cookie below 200 octets. This should make NTS more reliable in networks where longer NTP packets are filtered as a mitigation against amplification attacks exploiting the ntpd mode 6/7 protocol.
457 lines
12 KiB
C
457 lines
12 KiB
C
/*
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chronyd/chronyc - Programs for keeping computer clocks accurate.
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**********************************************************************
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* Copyright (C) Miroslav Lichvar 2020-2021
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of version 2 of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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**********************************************************************
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=======================================================================
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NTS-KE client
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*/
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#include "config.h"
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#include "sysincl.h"
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#include "nts_ke_client.h"
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#include "conf.h"
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#include "logging.h"
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#include "memory.h"
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#include "nameserv_async.h"
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#include "nts_ke_session.h"
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#include "siv.h"
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#include "socket.h"
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#include "util.h"
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#define CLIENT_TIMEOUT 16.0
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struct NKC_Instance_Record {
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char *name;
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IPSockAddr address;
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NKSN_Credentials credentials;
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NKSN_Instance session;
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int destroying;
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int got_response;
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int resolving_name;
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NKE_Context context;
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NKE_Cookie cookies[NKE_MAX_COOKIES];
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int num_cookies;
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char server_name[NKE_MAX_RECORD_BODY_LENGTH + 2];
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IPSockAddr ntp_address;
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};
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/* ================================================== */
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static NKSN_Credentials default_credentials = NULL;
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static int default_credentials_refs = 0;
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/* ================================================== */
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static void
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name_resolve_handler(DNS_Status status, int n_addrs, IPAddr *ip_addrs, void *arg)
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{
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NKC_Instance inst = arg;
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int i;
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inst->resolving_name = 0;
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if (inst->destroying) {
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Free(inst);
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return;
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}
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if (status != DNS_Success || n_addrs < 1) {
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LOG(LOGS_ERR, "Could not resolve NTP server %s from %s", inst->server_name, inst->name);
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/* Force restart */
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inst->got_response = 0;
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return;
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}
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inst->ntp_address.ip_addr = ip_addrs[0];
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/* Prefer an address in the same family as the NTS-KE server */
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for (i = 0; i < n_addrs; i++) {
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DEBUG_LOG("%s resolved to %s", inst->server_name, UTI_IPToString(&ip_addrs[i]));
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if (ip_addrs[i].family == inst->address.ip_addr.family) {
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inst->ntp_address.ip_addr = ip_addrs[i];
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break;
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}
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}
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}
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/* ================================================== */
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static int
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prepare_request(NKC_Instance inst)
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{
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NKSN_Instance session = inst->session;
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uint16_t data[2];
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int length;
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NKSN_BeginMessage(session);
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data[0] = htons(NKE_NEXT_PROTOCOL_NTPV4);
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if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, data, sizeof (data[0])))
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return 0;
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length = 0;
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if (SIV_GetKeyLength(AEAD_AES_128_GCM_SIV) > 0)
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data[length++] = htons(AEAD_AES_128_GCM_SIV);
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if (SIV_GetKeyLength(AEAD_AES_SIV_CMAC_256) > 0)
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data[length++] = htons(AEAD_AES_SIV_CMAC_256);
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if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, data,
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length * sizeof (data[0])))
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return 0;
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if (!NKSN_EndMessage(session))
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return 0;
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return 1;
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}
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/* ================================================== */
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static int
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process_response(NKC_Instance inst)
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{
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int next_protocol = -1, aead_algorithm = -1, error = 0;
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int i, critical, type, length;
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uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];
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assert(NKE_MAX_COOKIE_LENGTH <= NKE_MAX_RECORD_BODY_LENGTH);
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assert(sizeof (data) % sizeof (uint16_t) == 0);
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assert(sizeof (uint16_t) == 2);
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inst->num_cookies = 0;
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inst->ntp_address.ip_addr.family = IPADDR_UNSPEC;
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inst->ntp_address.port = 0;
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inst->server_name[0] = '\0';
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while (!error) {
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if (!NKSN_GetRecord(inst->session, &critical, &type, &length, &data, sizeof (data)))
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break;
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if (length > sizeof (data)) {
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DEBUG_LOG("Record too long type=%d length=%d critical=%d", type, length, critical);
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if (critical)
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error = 1;
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continue;
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}
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switch (type) {
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case NKE_RECORD_NEXT_PROTOCOL:
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if (!critical || length != 2 || ntohs(data[0]) != NKE_NEXT_PROTOCOL_NTPV4) {
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DEBUG_LOG("Unexpected NTS-KE next protocol");
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error = 1;
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break;
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}
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next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
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break;
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case NKE_RECORD_AEAD_ALGORITHM:
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if (length != 2 || (ntohs(data[0]) != AEAD_AES_SIV_CMAC_256 &&
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ntohs(data[0]) != AEAD_AES_128_GCM_SIV) ||
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SIV_GetKeyLength(ntohs(data[0])) <= 0) {
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DEBUG_LOG("Unexpected NTS-KE AEAD algorithm");
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error = 1;
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break;
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}
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aead_algorithm = ntohs(data[0]);
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inst->context.algorithm = aead_algorithm;
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break;
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case NKE_RECORD_ERROR:
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if (length == 2)
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DEBUG_LOG("NTS-KE error %d", ntohs(data[0]));
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error = 1;
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break;
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case NKE_RECORD_WARNING:
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if (length == 2)
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DEBUG_LOG("NTS-KE warning %d", ntohs(data[0]));
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error = 1;
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break;
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case NKE_RECORD_COOKIE:
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DEBUG_LOG("Got cookie length=%d", length);
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if (length < 1 || length > NKE_MAX_COOKIE_LENGTH || length % 4 != 0 ||
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inst->num_cookies >= NKE_MAX_COOKIES) {
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DEBUG_LOG("Unexpected length/cookie");
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break;
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}
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assert(NKE_MAX_COOKIE_LENGTH == sizeof (inst->cookies[inst->num_cookies].cookie));
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assert(NKE_MAX_COOKIES == sizeof (inst->cookies) /
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sizeof (inst->cookies[inst->num_cookies]));
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inst->cookies[inst->num_cookies].length = length;
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memcpy(inst->cookies[inst->num_cookies].cookie, data, length);
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inst->num_cookies++;
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break;
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case NKE_RECORD_NTPV4_SERVER_NEGOTIATION:
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if (length < 1 || length >= sizeof (inst->server_name)) {
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DEBUG_LOG("Invalid server name");
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error = 1;
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break;
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}
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memcpy(inst->server_name, data, length);
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inst->server_name[length] = '\0';
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/* Make sure the name is printable and has no spaces */
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for (i = 0; i < length && isgraph((unsigned char)inst->server_name[i]); i++)
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;
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if (i != length) {
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DEBUG_LOG("Invalid server name");
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error = 1;
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break;
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}
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DEBUG_LOG("Negotiated server %s", inst->server_name);
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break;
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case NKE_RECORD_NTPV4_PORT_NEGOTIATION:
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if (length != 2) {
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DEBUG_LOG("Invalid port");
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error = 1;
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break;
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}
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inst->ntp_address.port = ntohs(data[0]);
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DEBUG_LOG("Negotiated port %d", inst->ntp_address.port);
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break;
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default:
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DEBUG_LOG("Unknown record type=%d length=%d critical=%d", type, length, critical);
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if (critical)
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error = 1;
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}
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}
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DEBUG_LOG("NTS-KE response: error=%d next=%d aead=%d",
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error, next_protocol, aead_algorithm);
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if (error || inst->num_cookies == 0 ||
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next_protocol != NKE_NEXT_PROTOCOL_NTPV4 ||
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aead_algorithm < 0)
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return 0;
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return 1;
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}
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/* ================================================== */
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static int
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handle_message(void *arg)
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{
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NKC_Instance inst = arg;
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if (!process_response(inst)) {
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LOG(LOGS_ERR, "Received invalid NTS-KE response from %s", inst->name);
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return 0;
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}
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if (!NKSN_GetKeys(inst->session, inst->context.algorithm,
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&inst->context.c2s, &inst->context.s2c))
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return 0;
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if (inst->server_name[0] != '\0') {
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if (inst->resolving_name)
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return 0;
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if (!UTI_StringToIP(inst->server_name, &inst->ntp_address.ip_addr)) {
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int length = strlen(inst->server_name);
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/* Add a trailing dot if not present to force the name to be
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resolved as a fully qualified domain name */
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if (length < 1 || length + 1 >= sizeof (inst->server_name))
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return 0;
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if (inst->server_name[length - 1] != '.') {
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inst->server_name[length] = '.';
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inst->server_name[length + 1] = '\0';
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}
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DNS_Name2IPAddressAsync(inst->server_name, name_resolve_handler, inst);
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inst->resolving_name = 1;
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}
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}
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inst->got_response = 1;
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return 1;
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}
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/* ================================================== */
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NKC_Instance
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NKC_CreateInstance(IPSockAddr *address, const char *name, uint32_t cert_set)
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{
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const char **trusted_certs;
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uint32_t *certs_ids;
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NKC_Instance inst;
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int n_certs;
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inst = MallocNew(struct NKC_Instance_Record);
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inst->address = *address;
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inst->name = Strdup(name);
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inst->session = NKSN_CreateInstance(0, inst->name, handle_message, inst);
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inst->resolving_name = 0;
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inst->destroying = 0;
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inst->got_response = 0;
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n_certs = CNF_GetNtsTrustedCertsPaths(&trusted_certs, &certs_ids);
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/* Share the credentials among clients using the default set of trusted
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certificates, which likely contains most certificates */
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if (cert_set == 0) {
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if (!default_credentials)
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default_credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
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n_certs, cert_set);
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inst->credentials = default_credentials;
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if (default_credentials)
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default_credentials_refs++;
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} else {
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inst->credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
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n_certs, cert_set);
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}
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return inst;
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}
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/* ================================================== */
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void
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NKC_DestroyInstance(NKC_Instance inst)
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{
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NKSN_DestroyInstance(inst->session);
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Free(inst->name);
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if (inst->credentials) {
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if (inst->credentials == default_credentials) {
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default_credentials_refs--;
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if (default_credentials_refs <= 0) {
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NKSN_DestroyCertCredentials(default_credentials);
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default_credentials = NULL;
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}
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} else {
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NKSN_DestroyCertCredentials(inst->credentials);
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}
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}
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/* If the asynchronous resolver is running, let the handler free
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the instance later */
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if (inst->resolving_name) {
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inst->destroying = 1;
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return;
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}
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Free(inst);
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}
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/* ================================================== */
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int
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NKC_Start(NKC_Instance inst)
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{
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IPSockAddr local_addr;
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char label[512], *iface;
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int sock_fd;
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assert(!NKC_IsActive(inst));
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inst->got_response = 0;
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if (!inst->credentials) {
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DEBUG_LOG("Missing client credentials");
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return 0;
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}
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/* Don't try to connect if missing the algorithm which all servers
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are required to support */
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if (SIV_GetKeyLength(AEAD_AES_SIV_CMAC_256) <= 0) {
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LOG(LOGS_ERR, "Missing AES-SIV-CMAC-256");
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return 0;
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}
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/* Follow the bindacqaddress and bindacqdevice settings */
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CNF_GetBindAcquisitionAddress(inst->address.ip_addr.family, &local_addr.ip_addr);
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local_addr.port = 0;
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iface = CNF_GetBindAcquisitionInterface();
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/* Make a label containing both the address and name of the server */
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if (snprintf(label, sizeof (label), "%s (%s)",
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UTI_IPSockAddrToString(&inst->address), inst->name) >= sizeof (label))
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;
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sock_fd = SCK_OpenTcpSocket(&inst->address, &local_addr, iface, 0);
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if (sock_fd < 0) {
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LOG(LOGS_ERR, "Could not connect to %s", label);
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return 0;
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}
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/* Start an NTS-KE session */
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if (!NKSN_StartSession(inst->session, sock_fd, label, inst->credentials, CLIENT_TIMEOUT)) {
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SCK_CloseSocket(sock_fd);
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return 0;
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}
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/* Send a request */
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if (!prepare_request(inst)) {
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DEBUG_LOG("Could not prepare NTS-KE request");
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NKSN_StopSession(inst->session);
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return 0;
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}
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return 1;
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}
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/* ================================================== */
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int
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NKC_IsActive(NKC_Instance inst)
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{
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return !NKSN_IsStopped(inst->session) || inst->resolving_name;
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}
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/* ================================================== */
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int
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NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
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NKE_Cookie *cookies, int *num_cookies, int max_cookies,
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IPSockAddr *ntp_address)
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{
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int i;
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if (!inst->got_response || inst->resolving_name)
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return 0;
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*context = inst->context;
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for (i = 0; i < inst->num_cookies && i < max_cookies; i++)
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cookies[i] = inst->cookies[i];
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*num_cookies = i;
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*ntp_address = inst->ntp_address;
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return 1;
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}
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/* ================================================== */
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int
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NKC_GetRetryFactor(NKC_Instance inst)
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{
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return NKSN_GetRetryFactor(inst->session);
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}
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