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ntp: truncate MACs in NTPv4 packets

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When sending an NTPv4 packet, truncate long MAC to 192 bits to follow
RFC 7822.
This commit is contained in:
Miroslav Lichvar 2016-11-29 12:59:57 +01:00
parent 89b127bf6c
commit 6c8588c13c
1 changed files with 10 additions and 2 deletions
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12
ntp_core.c
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@ -849,7 +849,7 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
)
{
NTP_Packet message;
int auth_len, length, ret, precision;
int auth_len, mac_len, length, ret, precision;
struct timespec local_receive, local_transmit;
NTP_int64 ts_fuzz;
@ -979,8 +979,16 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
DEBUG_LOG(LOGF_NtpCore, "Could not generate auth data with key %"PRIu32, key_id);
return 0;
}
message.auth_keyid = htonl(key_id);
length += sizeof (message.auth_keyid) + auth_len;
mac_len = sizeof (message.auth_keyid) + auth_len;
/* Truncate MACs in NTPv4 packets to allow deterministic parsing
of extension fields (RFC 7822) */
if (version == 4 && mac_len > NTP_MAX_V4_MAC_LENGTH)
mac_len = NTP_MAX_V4_MAC_LENGTH;
length += mac_len;
} else if (auth_mode == AUTH_MSSNTP) {
/* MS-SNTP packets are signed (asynchronously) by ntp_signd */
return NSD_SignAndSendPacket(key_id, &message, where_to, from, length);