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chrony/ntp_signd.c
Miroslav Lichvar eae4b2abe5 ntp: drop precompensation of TX timestamp 
The daemon transmit timestamps are precompensated for the time it takes
to generate a MAC using a symmetric key (as measured on chronyd start)
and also an average round-trip time of the Samba signing of MS-SNTP
responses. This improves accuracy of the transmit timestamp, but it
has some issues.

The correction has a random error which is changing over time due to
variable CPU frequency, system load, migration to a different machine,
etc. If the measured delay is too large, the correction may cause the
transmit timestamp to be later than the actual transmission. Also, the
delay is measured for a packet of a minimal length with no extension
fields, and there is no support for NTS.

Drop the precompensation in favor of the interleaved mode, which now
avoids the authentication delay even when no kernel/hardware timestamps
are available.
2020-07-09 14:46:57 +02:00

341 lines
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/*
chronyd/chronyc - Programs for keeping computer clocks accurate.
**********************************************************************
* Copyright (C) Miroslav Lichvar 2016
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* 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, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
**********************************************************************
=======================================================================
Support for MS-SNTP authentication in Samba (ntp_signd)
*/
#include "config.h"
#include "sysincl.h"
#include "array.h"
#include "conf.h"
#include "logging.h"
#include "ntp_io.h"
#include "ntp_signd.h"
#include "sched.h"
#include "socket.h"
#include "util.h"
/* Declarations per samba/source4/librpc/idl/ntp_signd.idl */
#define SIGND_VERSION 0
typedef enum {
SIGN_TO_CLIENT = 0,
ASK_SERVER_TO_SIGN = 1,
CHECK_SERVER_SIGNATURE = 2,
SIGNING_SUCCESS = 3,
SIGNING_FAILURE = 4,
} SigndOp;
typedef struct {
uint32_t length;
uint32_t version;
uint32_t op;
uint16_t packet_id;
uint16_t _pad;
uint32_t key_id;
NTP_Packet packet_to_sign;
} SigndRequest;
typedef struct {
uint32_t length;
uint32_t version;
uint32_t op;
uint32_t packet_id;
NTP_Packet signed_packet;
} SigndResponse;
typedef struct {
NTP_Remote_Address remote_addr;
NTP_Local_Address local_addr;
int sent;
int received;
int request_length;
struct timespec request_ts;
SigndRequest request;
SigndResponse response;
} SignInstance;
/* As the communication with ntp_signd is asynchronous, incoming packets are
saved in a queue in order to avoid loss when they come in bursts */
#define MAX_QUEUE_LENGTH 16U
#define NEXT_QUEUE_INDEX(index) (((index) + 1) % MAX_QUEUE_LENGTH)
#define IS_QUEUE_EMPTY() (queue_head == queue_tail)
/* Fixed-size array of SignInstance */
static ARR_Instance queue;
static unsigned int queue_head;
static unsigned int queue_tail;
#define INVALID_SOCK_FD (-6)
/* Unix domain socket connected to ntp_signd */
static int sock_fd;
/* Flag indicating if the MS-SNTP authentication is enabled */
static int enabled;
/* ================================================== */
static void read_write_socket(int sock_fd, int event, void *anything);
/* ================================================== */
static void
close_socket(void)
{
SCH_RemoveFileHandler(sock_fd);
SCK_CloseSocket(sock_fd);
sock_fd = INVALID_SOCK_FD;
/* Empty the queue */
queue_head = queue_tail = 0;
}
/* ================================================== */
static int
open_socket(void)
{
char path[PATH_MAX];
if (sock_fd != INVALID_SOCK_FD)
return 1;
if (snprintf(path, sizeof (path), "%s/socket", CNF_GetNtpSigndSocket()) >= sizeof (path)) {
DEBUG_LOG("signd socket path too long");
return 0;
}
sock_fd = SCK_OpenUnixStreamSocket(path, NULL, 0);
if (sock_fd < 0) {
sock_fd = INVALID_SOCK_FD;
return 0;
}
SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, read_write_socket, NULL);
return 1;
}
/* ================================================== */
static void
process_response(SignInstance *inst)
{
struct timespec ts;
double delay;
if (ntohs(inst->request.packet_id) != ntohl(inst->response.packet_id)) {
DEBUG_LOG("Invalid response ID");
return;
}
if (ntohl(inst->response.op) != SIGNING_SUCCESS) {
DEBUG_LOG("Signing failed");
return;
}
/* Check if the file descriptor is still valid */
if (!NIO_IsServerSocket(inst->local_addr.sock_fd)) {
DEBUG_LOG("Invalid NTP socket");
return;
}
SCH_GetLastEventTime(NULL, NULL, &ts);
delay = UTI_DiffTimespecsToDouble(&ts, &inst->request_ts);
DEBUG_LOG("Signing succeeded (delay %f)", delay);
/* Send the signed NTP packet */
NIO_SendPacket(&inst->response.signed_packet, &inst->remote_addr, &inst->local_addr,
ntohl(inst->response.length) + sizeof (inst->response.length) -
offsetof(SigndResponse, signed_packet), 0);
}
/* ================================================== */
static void
read_write_socket(int sock_fd, int event, void *anything)
{
SignInstance *inst;
uint32_t response_length;
int s;
inst = ARR_GetElement(queue, queue_head);
if (event == SCH_FILE_OUTPUT) {
assert(!IS_QUEUE_EMPTY());
assert(inst->sent < inst->request_length);
if (!inst->sent)
SCH_GetLastEventTime(NULL, NULL, &inst->request_ts);
s = SCK_Send(sock_fd, (char *)&inst->request + inst->sent,
inst->request_length - inst->sent, 0);
if (s < 0) {
close_socket();
return;
}
inst->sent += s;
/* Try again later if the request is not complete yet */
if (inst->sent < inst->request_length)
return;
/* Disable output and wait for a response */
SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 0);
}
if (event == SCH_FILE_INPUT) {
if (IS_QUEUE_EMPTY()) {
DEBUG_LOG("Unexpected signd response");
close_socket();
return;
}
assert(inst->received < sizeof (inst->response));
s = SCK_Receive(sock_fd, (char *)&inst->response + inst->received,
sizeof (inst->response) - inst->received, 0);
if (s <= 0) {
close_socket();
return;
}
inst->received += s;
if (inst->received < sizeof (inst->response.length))
return;
response_length = ntohl(inst->response.length) + sizeof (inst->response.length);
if (response_length < offsetof(SigndResponse, signed_packet) ||
response_length > sizeof (SigndResponse)) {
DEBUG_LOG("Invalid response length");
close_socket();
return;
}
/* Wait for more data if not complete yet */
if (inst->received < response_length)
return;
process_response(inst);
/* Move the head and enable output for the next packet */
queue_head = NEXT_QUEUE_INDEX(queue_head);
if (!IS_QUEUE_EMPTY())
SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);
}
}
/* ================================================== */
void
NSD_Initialise()
{
sock_fd = INVALID_SOCK_FD;
enabled = CNF_GetNtpSigndSocket() && CNF_GetNtpSigndSocket()[0];
if (!enabled)
return;
queue = ARR_CreateInstance(sizeof (SignInstance));
ARR_SetSize(queue, MAX_QUEUE_LENGTH);
queue_head = queue_tail = 0;
LOG(LOGS_INFO, "MS-SNTP authentication enabled");
}
/* ================================================== */
void
NSD_Finalise()
{
if (!enabled)
return;
if (sock_fd != INVALID_SOCK_FD)
close_socket();
ARR_DestroyInstance(queue);
}
/* ================================================== */
int
NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_PacketInfo *info,
NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr)
{
SignInstance *inst;
if (!enabled) {
DEBUG_LOG("signd disabled");
return 0;
}
if (queue_head == NEXT_QUEUE_INDEX(queue_tail)) {
DEBUG_LOG("signd queue full");
return 0;
}
if (info->length != NTP_HEADER_LENGTH) {
DEBUG_LOG("Invalid packet length");
return 0;
}
if (!open_socket())
return 0;
inst = ARR_GetElement(queue, queue_tail);
inst->remote_addr = *remote_addr;
inst->local_addr = *local_addr;
inst->sent = 0;
inst->received = 0;
inst->request_length = offsetof(SigndRequest, packet_to_sign) + info->length;
/* The length field doesn't include itself */
inst->request.length = htonl(inst->request_length - sizeof (inst->request.length));
inst->request.version = htonl(SIGND_VERSION);
inst->request.op = htonl(SIGN_TO_CLIENT);
inst->request.packet_id = htons(queue_tail);
inst->request._pad = 0;
inst->request.key_id = htonl(key_id);
memcpy(&inst->request.packet_to_sign, packet, info->length);
/* Enable output if there was no pending request */
if (IS_QUEUE_EMPTY())
SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);
queue_tail = NEXT_QUEUE_INDEX(queue_tail);
DEBUG_LOG("Packet added to signd queue (%u:%u)", queue_head, queue_tail);
return 1;
}
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