.\" Copyright (c) 2018 Ian Lepore <ian@FreeBSD.org>
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.Dd July 20, 2018
.Dt MAC_NTPD 4
.Os
.Sh NAME
.Nm mac_ntpd
.Nd "policy allowing ntpd to run as non-root user"
.Sh SYNOPSIS
To compile the ntpd policy into your kernel, place the following lines
in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Cd "options MAC_NTPD"
.Ed
.Pp
Alternately, to load the ntpd policy module at boot time,
place the following line in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Ed
.Pp
and in
.Xr loader.conf 5 :
.Bd -literal -offset indent
mac_ntpd_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
policy grants any process running as user
.Sq ntpd
(uid 123) the privileges needed to manipulate
system time, and to (re-)bind to the privileged NTP port.
.Pp
When
.Xr ntpd 8
is started with
.Sq Fl u Ar <user>[:group]
on the command line, it performs all initializations requiring root
privileges, then drops root privileges by switching to the given user id.
From that point on, the only privileges it requires are the ability
to manipulate system time, and the ability to re-bind a UDP socket
to the NTP port (port 123) after a network interface change.
.Pp
With the
.Nm
policy active, it may also be possible to start ntpd as a non-root user,
because the default ntpd options don't require any additional root
privileges beyond those granted by the policy.
.Pp
.Ss Privileges Granted
The exact set of kernel privileges granted to any process running
with the configured uid is:
.Bl -inset -compact -offset indent
.It Dv PRIV_ADJTIME
.It Dv PRIV_CLOCK_SETTIME
.It Dv PRIV_NTP_ADJTIME
.It Dv PRIV_NETINET_RESERVEDPORT
.It Dv PRIV_NETINET_REUSEPORT
.El
.Pp
.Ss Runtime Configuration
The following
.Xr sysctl 8
MIBs are available for fine-tuning this MAC policy.
All
.Xr sysctl 8
variables can also be set as
.Xr loader 8
tunables in
.Xr loader.conf 5 .
.Bl -tag -width indent
.It Va security.mac.ntpd.enabled
Enable the
.Nm
policy.
(Default: 1).
.It Va security.mac.ntpd.uid
The numeric uid of the ntpd user.
(Default: 123).
.El
.Sh SEE ALSO
.Xr mac 4 ,
.Xr ntpd 8
.Sh HISTORY
MAC first appeared in
.Fx 5.0
and
.Nm
first appeared in
.Fx 12.0 .