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/*
chronyd/chronyc - Programs for keeping computer clocks accurate.
**********************************************************************
* Copyright (C) Miroslav Lichvar 2019-2020
*
* 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.
*
**********************************************************************
=======================================================================
Functions for adding and parsing NTPv4 extension fields
*/
#include "config.h"
#include "sysincl.h"
#include "ntp_ext.h"
struct ExtFieldHeader {
uint16_t type;
uint16_t length;
};
/* ================================================== */
static int
format_field(unsigned char *buffer, int buffer_length, int start,
int type, int body_length, int *length, void **body)
{
struct ExtFieldHeader *header;
if (buffer_length < 0 || start < 0 || buffer_length <= start ||
buffer_length - start < sizeof (*header) || start % 4 != 0)
return 0;
header = (struct ExtFieldHeader *)(buffer + start);
if (body_length < 0 || sizeof (*header) + body_length > 0xffff ||
start + sizeof (*header) + body_length > buffer_length || body_length % 4 != 0)
return 0;
header->type = htons(type);
header->length = htons(sizeof (*header) + body_length);
*length = sizeof (*header) + body_length;
*body = header + 1;
return 1;
}
/* ================================================== */
int
NEF_SetField(unsigned char *buffer, int buffer_length, int start,
int type, void *body, int body_length, int *length)
{
void *ef_body;
if (!format_field(buffer, buffer_length, start, type, body_length, length, &ef_body))
return 0;
memcpy(ef_body, body, body_length);
return 1;
}
/* ================================================== */
int
NEF_AddBlankField(NTP_Packet *packet, NTP_PacketInfo *info, int type, int body_length, void **body)
{
int ef_length, length = info->length;
if (length < NTP_HEADER_LENGTH || length >= sizeof (*packet) || length % 4 != 0)
return 0;
/* Only NTPv4 packets can have extension fields */
if (info->version != 4)
return 0;
if (!format_field((unsigned char *)packet, sizeof (*packet), length,
type, body_length, &ef_length, body))
return 0;
if (ef_length < NTP_MIN_EF_LENGTH)
return 0;
info->length += ef_length;
info->ext_fields++;
return 1;
}
/* ================================================== */
int
NEF_AddField(NTP_Packet *packet, NTP_PacketInfo *info,
int type, void *body, int body_length)
{
void *ef_body;
if (!NEF_AddBlankField(packet, info, type, body_length, &ef_body))
return 0;
memcpy(ef_body, body, body_length);
return 1;
}
/* ================================================== */
int
NEF_ParseSingleField(unsigned char *buffer, int buffer_length, int start,
int *length, int *type, void **body, int *body_length)
{
struct ExtFieldHeader *header;
int ef_length;
if (buffer_length < 0 || start < 0 || buffer_length <= start ||
buffer_length - start < sizeof (*header))
return 0;
header = (struct ExtFieldHeader *)(buffer + start);
assert(sizeof (*header) == 4);
ef_length = ntohs(header->length);
if (ef_length < (int)(sizeof (*header)) || start + ef_length > buffer_length ||
ef_length % 4 != 0)
return 0;
if (length)
*length = ef_length;
if (type)
*type = ntohs(header->type);
if (body)
*body = header + 1;
if (body_length)
*body_length = ef_length - sizeof (*header);
return 1;
}
/* ================================================== */
int
NEF_ParseField(NTP_Packet *packet, int packet_length, int start,
int *length, int *type, void **body, int *body_length)
{
int ef_length;
if (packet_length <= NTP_HEADER_LENGTH || packet_length > sizeof (*packet) ||
packet_length <= start || packet_length % 4 != 0 ||
start < NTP_HEADER_LENGTH || start % 4 != 0)
return 0;
/* Only NTPv4 packets have extension fields */
if (NTP_LVM_TO_VERSION(packet->lvm) != 4)
return 0;
/* Check if the remaining data is a MAC. RFC 7822 specifies the maximum
length of a MAC in NTPv4 packets in order to enable deterministic
parsing. */
if (packet_length - start <= NTP_MAX_V4_MAC_LENGTH)
return 0;
if (!NEF_ParseSingleField((unsigned char *)packet, packet_length, start,
&ef_length, type, body, body_length))
return 0;
if (ef_length < NTP_MIN_EF_LENGTH)
return 0;
if (length)
*length = ef_length;
return 1;
}
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