freebsd-dev/sys/security/mac_ntpd/mac_ntpd.c
Ian Lepore 3496c981ac Make it possible to run ntpd as a non-root user, add ntpd uid and gid.
Code analysis and runtime analysis using truss(8) indicate that the only
privileged operations performed by ntpd are adjusting system time, and
(re-)binding to privileged UDP port 123. These changes add a new mac(4)
policy module, mac_ntpd(4), which grants just those privileges to any
process running with uid 123.

This also adds a new user and group, ntpd:ntpd, (uid:gid 123:123), and makes
them the owner of the /var/db/ntp directory, so that it can be used as a
location where the non-privileged daemon can write files such as the
driftfile, and any optional logfile or stats files.

Because there are so many ways to configure ntpd, the question of how to
configure it to run without root privs can be a bit complex, so that will be
addressed in a separate commit. These changes are just what's required to
grant the limited subset of privs to ntpd, and the small change to ntpd to
prevent it from exiting with an error if running as non-root.

Differential Revision:	https://reviews.freebsd.org/D16281
2018-07-19 23:55:29 +00:00

78 lines
2.4 KiB
C

/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2018 Ian Lepore <ian@FreeBSD.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/priv.h>
#include <sys/sysctl.h>
#include <sys/ucred.h>
#include <security/mac/mac_policy.h>
SYSCTL_DECL(_security_mac);
static SYSCTL_NODE(_security_mac, OID_AUTO, ntpd, CTLFLAG_RW, 0,
"mac_ntpd policy controls");
static int ntpd_enabled = 1;
SYSCTL_INT(_security_mac_ntpd, OID_AUTO, enabled, CTLFLAG_RWTUN,
&ntpd_enabled, 0, "Enable mac_ntpd policy");
static int ntpd_uid = 123;
SYSCTL_INT(_security_mac_ntpd, OID_AUTO, uid, CTLFLAG_RWTUN,
&ntpd_uid, 0, "User id for ntpd user");
static int
ntpd_priv_grant(struct ucred *cred, int priv)
{
if (ntpd_enabled && cred->cr_uid == ntpd_uid) {
switch (priv) {
case PRIV_ADJTIME:
case PRIV_CLOCK_SETTIME:
case PRIV_NTP_ADJTIME:
case PRIV_NETINET_RESERVEDPORT:
case PRIV_NETINET_REUSEPORT:
return (0);
default:
break;
}
}
return (EPERM);
}
static struct mac_policy_ops ntpd_ops =
{
.mpo_priv_grant = ntpd_priv_grant,
};
MAC_POLICY_SET(&ntpd_ops, mac_ntpd, "MAC/ntpd",
MPC_LOADTIME_FLAG_UNLOADOK, NULL);