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Make it possible to run ntpd as a non-root user, add ntpd uid and gid.

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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
This commit is contained in:
Ian Lepore 2018-07-19 23:55:29 +00:00
parent dbe8ed38bf
commit 3496c981ac
12 changed files with 232 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
contrib/ntp/ntpd/ntpd.c
View File

@ -123,6 +123,9 @@
#if defined(HAVE_PRIV_H) && defined(HAVE_SOLARIS_PRIVS)
# include <priv.h>
#endif /* HAVE_PRIV_H */
#if defined(HAVE_TRUSTEDBSD_MAC)
# include <sys/mac.h>
#endif /* HAVE_TRUSTEDBSD_MAC */
#endif /* HAVE_DROPROOT */
#if defined (LIBSECCOMP) && (KERN_SECCOMP)
@ -634,7 +637,12 @@ ntpdmain(
/* MPE lacks the concept of root */
# if defined(HAVE_GETUID) && !defined(MPE)
uid = getuid();
if (uid && !HAVE_OPT( SAVECONFIGQUIT )) {
if (uid && !HAVE_OPT( SAVECONFIGQUIT )
# if defined(HAVE_TRUSTEDBSD_MAC)
/* We can run as non-root if the mac_ntpd policy is enabled. */
&& mac_is_present("ntpd") != 1
# endif
) {
msyslog_term = TRUE;
msyslog(LOG_ERR,
"must be run as root, not uid %ld", (long)uid);
@ -1082,7 +1090,17 @@ ntpdmain(
exit (-1);
}
# if !defined(HAVE_LINUX_CAPABILITIES) && !defined(HAVE_SOLARIS_PRIVS)
# if defined(HAVE_TRUSTEDBSD_MAC)
/*
* To manipulate system time and (re-)bind to NTP_PORT as needed
* following interface changes, we must either run as uid 0 or
* the mac_ntpd policy module must be enabled.
*/
if (sw_uid != 0 && mac_is_present("ntpd") != 1) {
msyslog(LOG_ERR, "Need MAC 'ntpd' policy enabled to drop root privileges");
exit (-1);
}
# elif !defined(HAVE_LINUX_CAPABILITIES) && !defined(HAVE_SOLARIS_PRIVS)
/*
* for now assume that the privilege to bind to privileged ports
* is associated with running with uid 0 - should be refined on

1
etc/group
View File

@ -29,6 +29,7 @@ dialer:*:68:
network:*:69:
audit:*:77:
www:*:80:
ntpd:*:123:
_ypldap:*:160:
hast:*:845:
nogroup:*:65533:

1
etc/master.passwd
View File

@ -22,6 +22,7 @@ uucp:*:66:66::0:0:UUCP pseudo-user:/var/spool/uucppublic:/usr/local/libexec/uucp
pop:*:68:6::0:0:Post Office Owner:/nonexistent:/usr/sbin/nologin
auditdistd:*:78:77::0:0:Auditdistd unprivileged user:/var/empty:/usr/sbin/nologin
www:*:80:80::0:0:World Wide Web Owner:/nonexistent:/usr/sbin/nologin
ntpd:*:123:123::0:0:NTP Daemon:/var/db/ntp:/usr/sbin/nologin
_ypldap:*:160:160::0:0:YP LDAP unprivileged user:/var/empty:/usr/sbin/nologin
hast:*:845:845::0:0:HAST unprivileged user:/var/empty:/usr/sbin/nologin
nobody:*:65534:65534::0:0:Unprivileged user:/nonexistent:/usr/sbin/nologin

2
etc/mtree/BSD.var.dist
View File

@ -46,7 +46,7 @@
..
ipf mode=0700
..
ntp mode=0700
ntp uname=ntpd gname=ntpd
..
pkg
..

116
share/man/man4/mac_ntpd.4 Normal file
View File

@ -0,0 +1,116 @@
.\" 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 AUTHORS 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 AUTHORS 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.
.\"
.\" $FreeBSD$
.\"
.Dd June 28, 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 :
.Pp
.Dl "mac_ntpd_load=""YES"""
.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 -u\ <user>
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.
By default,
.Fx
starts
.Xr ntpd 8
with
.Sq -u\ ntpd:ntpd
on the command line, if the mac_ntpd policy is available to grant
the required privileges.
.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 PRIV_ADJTIME
.It PRIV_CLOCK_SETTIME
.It PRIV_NTP_ADJTIME
.It PRIV_NETINET_RESERVEDPORT
.It 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 .

1
sys/conf/NOTES
View File

@ -1193,6 +1193,7 @@ options MAC_IFOFF
options MAC_LOMAC
options MAC_MLS
options MAC_NONE
options MAC_NTPD
options MAC_PARTITION
options MAC_PORTACL
options MAC_SEEOTHERUIDS

1
sys/conf/files
View File

@ -4887,6 +4887,7 @@ security/mac_ifoff/mac_ifoff.c optional mac_ifoff
security/mac_lomac/mac_lomac.c optional mac_lomac
security/mac_mls/mac_mls.c optional mac_mls
security/mac_none/mac_none.c optional mac_none
security/mac_ntpd/mac_ntpd.c optional mac_ntpd
security/mac_partition/mac_partition.c optional mac_partition
security/mac_portacl/mac_portacl.c optional mac_portacl
security/mac_seeotheruids/mac_seeotheruids.c optional mac_seeotheruids

1
sys/conf/options
View File

@ -158,6 +158,7 @@ MAC_IFOFF opt_dontuse.h
MAC_LOMAC opt_dontuse.h
MAC_MLS opt_dontuse.h
MAC_NONE opt_dontuse.h
MAC_NTPD opt_dontuse.h
MAC_PARTITION opt_dontuse.h
MAC_PORTACL opt_dontuse.h
MAC_SEEOTHERUIDS opt_dontuse.h

1
sys/modules/Makefile
View File

@ -230,6 +230,7 @@ SUBDIR= \
mac_lomac \
mac_mls \
mac_none \
mac_ntpd \
mac_partition \
mac_portacl \
mac_seeotheruids \

8
sys/modules/mac_ntpd/Makefile Normal file
View File

@ -0,0 +1,8 @@
# $FreeBSD$
.PATH: ${SRCTOP}/sys/security/mac_ntpd
KMOD= mac_ntpd
SRCS= mac_ntpd.c
.include <bsd.kmod.mk>

77
sys/security/mac_ntpd/mac_ntpd.c Normal file
View File

@ -0,0 +1,77 @@
/*-
* 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);

5
usr.sbin/ntp/config.h
View File

@ -392,7 +392,7 @@
/* #undef HAVE_DOPRNT */
/* Can we drop root privileges? */
/* #undef HAVE_DROPROOT */
#define HAVE_DROPROOT
/* Define to 1 if you have the <errno.h> header file. */
#define HAVE_ERRNO_H 1
@ -1119,6 +1119,9 @@
/* Do we have the TIO serial stuff? */
/* #undef HAVE_TIO_SERIAL_STUFF */
/* Are TrustedBSD MAC policy privileges available? */
#define HAVE_TRUSTEDBSD_MAC 1
/* Define to 1 if the system has the type `uint16_t'. */
#define HAVE_UINT16_T 1