diff options
Diffstat (limited to 'ntp_ext.c')
| -rw-r--r-- | ntp_ext.c | 192 |
1 files changed, 192 insertions, 0 deletions
diff --git a/ntp_ext.c b/ntp_ext.c new file mode 100644 index 0000000..d2babb1 --- /dev/null +++ b/ntp_ext.c @@ -0,0 +1,192 @@ +/* + 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; +} |