In client packets set the leap, stratum, reference ID, reference time,
root delay and root dispersion to constant values to not reveal the
state of the synchronization. Use precision 32 to make the receive and
transmit timestamps completely random and not reveal the local time.
Use UTI_GetRandomBytes() instead of random() to generate random bits
below precision. Save the result in NTP_int64 in the network order and
allow precision in the full range from -32 to 32. With precision 32
the fuzzing now makes the timestamp completely random and can be used to
hide the time.
After sending a client packet, schedule a timeout to close the socket
at the time when all server replies would fail the delay test, so the
socket is not open for longer than necessary (e.g. when the server is
unreachable). With the default maxdelay of 3 seconds the timeout is 7
seconds.
For testA in the client mode require also that the time the server
needed to process the client request is not longer than 4 seconds.
With maximum peer delay this limits the interval in which the client can
accept a server reply.
Timeout ID of zero can be now safely used to indicate that the timer is
not running. Remove the extra timer_running variables that were
necessary to track that.
Set refid in server/broadcast packets to 127.127.1.255 when a time
smoothing offset is applied to the timestamps. This allows the clients
and administrators to detect that the server is not serving its best
estimate of the true time.
Time smoothing determines an offset that needs to be applied to the
cooked time to make it smooth for external observers. Observed offset
and frequency change slowly and there are no discontinuities. This can
be used on an NTP server to make it easier for the clients to track the
time and keep their clocks close together even when large offset or
frequency corrections are applied to the server's clock (e.g. after
being offline for longer time).
Accumulated offset and frequency are smoothed out in three stages. In
the first stage, the frequency is changed at a constant rate (wander) up
to a maximum, in the second stage the frequency stays at the maximum for
as long as needed and in the third stage the frequency is brought back
to zero.
Time smoothing is configured by the smoothtime directive. It takes two
arguments, maximum frequency offset and maximum wander. It's disabled by
default.
An attacker knowing that NTP hosts A and B are peering with each other
(symmetric association) can send a packet with random timestamps to host
A with source address of B which will set the NTP state variables on A
to the values sent by the attacker. Host A will then send on its next
poll to B a packet with originate timestamp that doesn't match the
transmit timestamp of B and the packet will be dropped. If the attacker
does this periodically for both hosts, they won't be able to synchronize
to each other. It is a denial-of-service attack.
According to [1], NTP authentication is supposed to protect symmetric
associations against this attack, but in the NTPv3 (RFC 1305) and NTPv4
(RFC 5905) specifications the state variables are updated before the
authentication check is performed, which means the association is
vulnerable to the attack even when authentication is enabled.
To fix this problem in chrony, save the originate and local timestamps
only when the authentication check (test5) passed.
[1] https://www.eecis.udel.edu/~mills/onwire.html
Server sockets are now explicitly opened and closed for normal NTP
server, NTP broadcast and NTP peering. This will allow closing the
NTP port when not needed.
The minsamples and maxsamples directives now set the default value,
which can be overriden for individual sources in the server/peer/pool
and refclock directives.
Add new functions to change source's reference ID/address and reset the
instance. Use that instead of destroying and creating a new instance
when the NTP address is changed.
When using server socket to send client requests (acquisitionport 123)
and currently not waiting for a reply, the socket check will fail for
client requests from the source.
The check needs to be moved to correctly handle the requests as from an
unknown source.
Don't stop online burst for unreachable sources until sending succeeds.
This is mainly useful with iburst when chronyd is started before the
network is configured.
Switch to NTP for presend as the echo service (RFC 862) is rarely
enabled. When presend is active, send an NTP client packet to the
server/peer and ignore the reply.
This also fixes presend with separate client sockets. The destination
port can't be changed on connected sockets, so the echo packet was sent
to the NTP port instead of the echo port.
NTP timestamps use only 32 bits to count seconds and the current NTP era
ends in 2036. Add support for converting NTP timestamps from other NTP
eras on systems with 64-bit time_t.
The earliest assumed NTP time is set by the configure script (by default
to 50 years before the date of the build) and earlier NTP timestamps
underflow to the following NTP era.
Create a new connected client socket before each request and close it
when a valid reply is received.
This is useful when the network configuration is changed and the client
socket should be reconnected, but the old bound address remains valid
and sendmsg() doesn't return with an error.
This will be needed to prevent loading of dump files after sources have
already accumulated samples and possibly reference was already updated
when async resolving of sources is implemented.
When source is set as active, it's receiving reachability updates (e.g.
offline NTP sources are not active).
Also add function to count active sources.
Explicitly set the number of iburst samples to the size of the register
to make sure there are at least 7 reachability updates and the
initstepslew mode can be ended.
If acquisitionport is set to 0 (default), create and connect a new
socket for each server instead of using one socket per address family
for all servers.
If the remote stratum is higher than ours, try to lock on the peer's
polling to minimize our response time by slightly extending our delay or
waiting for the peer to catch up with us as the random part in the
actual interval is reduced. If the remote stratum is equal to ours, try
to interleave evenly with the peer.
If the remote peer uses a polling interval shorter than the local
minimum, the local peer will be unable to send any packets as the
timeout will be updated on every received valid packet and will never
expire.
Modify the delay calculation to aim at poll interval away since the last
transmit.
Also, share the delay calculation code with transmit_timeout().
This should prevent chronyd from getting stuck and refusing new samples
due to failing test4 when the current measured frequency offset is close
to 1.0. That can happen when the system clock is stepped forward behind
chronyd's back.
