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ntp: avoid truncation of NTPv4 MACs by default

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If the MAC in NTPv4 requests would be truncated, use version 3 by
default to avoid the truncation. This is necessary for compatibility
with older chronyd servers, which do not respond to messages with
truncated MACs.
This commit is contained in:
Miroslav Lichvar
2016-11-29 13:26:46 +01:00
parent 1d5d768545
commit e6e9a472db
5 changed files with 34 additions and 9 deletions
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14
ntp_core.c
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@@ -520,11 +520,7 @@ NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourcePar
result->auto_offline = params->auto_offline;
result->poll_target = params->poll_target;
result->version = params->version;
if (result->version < NTP_MIN_COMPAT_VERSION)
result->version = NTP_MIN_COMPAT_VERSION;
else if (result->version > NTP_VERSION)
result->version = NTP_VERSION;
result->version = NTP_VERSION;
if (params->authkey == INACTIVE_AUTHKEY) {
result->auth_mode = AUTH_NONE;
@@ -541,8 +537,16 @@ NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourcePar
result->auth_key_id, UTI_IPToString(&result->remote_addr.ip_addr),
"too short");
}
/* If the MAC in NTPv4 packets would be truncated, use version 3 by
default for compatibility with older chronyd servers */
if (KEY_GetAuthLength(result->auth_key_id) + 4 > NTP_MAX_V4_MAC_LENGTH)
result->version = 3;
}
if (params->version)
result->version = CLAMP(NTP_MIN_COMPAT_VERSION, params->version, NTP_VERSION);
/* Create a source instance for this NTP source */
result->source = SRC_CreateNewInstance(UTI_IPToRefid(&remote_addr->ip_addr),
SRC_NTP, params->sel_options,