107 lines
3 KiB
C
107 lines
3 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 2019
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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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Functions for working with NTP extension fields
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*/
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#include "config.h"
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#include "sysincl.h"
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#include "ntp_ext.h"
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struct ExtFieldHeader {
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uint16_t type;
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uint16_t length;
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};
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/* ================================================== */
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int
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NEF_ParseSingleField(unsigned char *buffer, int buffer_length, int start,
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int *length, int *type, void **body, int *body_length)
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{
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struct ExtFieldHeader *header;
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int ef_length;
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if (buffer_length < 0 || start < 0 || buffer_length <= start ||
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buffer_length - start < sizeof (*header))
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return 0;
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header = (struct ExtFieldHeader *)(buffer + start);
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assert(sizeof (*header) == 4);
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ef_length = ntohs(header->length);
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if (ef_length < (int)(sizeof (*header)) || start + ef_length > buffer_length ||
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ef_length % 4 != 0)
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return 0;
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if (length)
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*length = ef_length;
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if (type)
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*type = ntohs(header->type);
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if (body)
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*body = header + 1;
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if (body_length)
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*body_length = ef_length - sizeof (*header);
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return 1;
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}
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/* ================================================== */
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int
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NEF_ParseField(NTP_Packet *packet, int packet_length, int start,
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int *length, int *type, void **body, int *body_length)
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{
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int ef_length;
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if (packet_length <= NTP_HEADER_LENGTH || packet_length > sizeof (*packet) ||
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packet_length <= start || packet_length % 4 != 0 ||
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start < NTP_HEADER_LENGTH || start % 4 != 0)
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return 0;
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/* Only NTPv4 packets have extension fields */
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if (NTP_LVM_TO_VERSION(packet->lvm) != 4)
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return 0;
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/* Check if the remaining data is a MAC. RFC 7822 specifies the maximum
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length of a MAC in NTPv4 packets in order to enable deterministic
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parsing. */
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if (packet_length - start <= NTP_MAX_V4_MAC_LENGTH)
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return 0;
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if (!NEF_ParseSingleField((unsigned char *)packet, packet_length, start,
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&ef_length, type, body, body_length))
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return 0;
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if (ef_length < NTP_MIN_EF_LENGTH)
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return 0;
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if (length)
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*length = ef_length;
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return 1;
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}
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