.\" Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
.\" All rights reserved.
.\"
.\" 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 March 18, 2018
.Dt CAP_SYSCTL 3
.Os
.Sh NAME
.Nm cap_sysctlbyname
.Nd "library for getting or setting system information in capability mode"
.Sh LIBRARY
.Lb libcap_sysctl
.Sh SYNOPSIS
.In sys/nv.h
.In libcasper.h
.In casper/cap_sysctl.h
.Ft int
.Fn cap_sysctlbyname "cap_channel_t *chan" " const char *name" " void *oldp" " size_t *oldlenp" " const void *newp" " size_t newlen"
.Sh DESCRIPTION
The function
.Fn cap_sysctlbyname
is equivalent to
.Xr sysctlbyname 3
except that the connection to the
.Nm system.sysctl
service needs to be provided.
.Sh LIMITS
The service can be limited using
.Xr cap_limit_set 3
function.
The
.Xr nvlist 9
for that function can contain the following values and types:
.Bl -ohang -offset indent
.It ( NV_TYPE_NUMBER )
The name of the element with type number will be treated as the limited sysctl.
The value of the element will describe the access rights for given sysctl.
There are four different rights
.Dv CAP_SYSCTL_READ ,
.Dv CAP_SYSCTL_WRITE ,
.Dv CAP_SYSCTL_RDWR ,
and
.Dv CAP_SYSCTL_RECURSIVE .
The
.Dv CAP_SYSCTL_READ
flag allows to fetch the value of a given sysctl.
The
.Dv CAP_SYSCTL_WIRTE
flag allows to override the value of a given sysctl.
The
.Dv CAP_SYSCTL_RDWR
is combination of the
.Dv CAP_SYSCTL_WIRTE
and
.Dv CAP_SYSCTL_READ
and allows to read and write the value of a given sysctl.
The
.Dv CAP_SYSCTL_RECURSIVE
allows access to all children of a given sysctl.
This right must be combined with at least one other right.
.Sh EXAMPLES
The following example first opens a capability to casper and then uses this
capability to create the
.Nm system.sysctl
casper service and uses it to get the value of
.Dv kern.trap_enotcap .
.Bd -literal
cap_channel_t *capcas, *capsysctl;
const char *name = "kern.trap_enotcap";
nvlist_t *limits;
int value;
size_t size;

/* Open capability to Casper. */
capcas = cap_init();
if (capcas == NULL)
	err(1, "Unable to contact Casper");

/* Enter capability mode sandbox. */
if (cap_enter() < 0 && errno != ENOSYS)
	err(1, "Unable to enter capability mode");

/* Use Casper capability to create capability to the system.sysctl service. */
capsysctl = cap_service_open(capcas, "system.sysctl");
if (capsysctl == NULL)
	err(1, "Unable to open system.sysctl service");

/* Close Casper capability, we don't need it anymore. */
cap_close(capcas);

/* Create limit for one MIB with read access only. */
limits = nvlist_create(0);
nvlist_add_number(limits, name, CAP_SYSCTL_READ);

/* Limit system.sysctl. */
if (cap_limit_set(capsysctl, limits) < 0)
	err(1, "Unable to set limits");

/* Fetch value. */
if (cap_sysctlbyname(capsysctl, name, &value, &size, NULL, 0) < 0)
	err(1, "Unable to get value of sysctl");

printf("The value of %s is %d.\\n", name, value);

cap_close(capsysctl);
.Ed
.Sh SEE ALSO
.Xr cap_enter 2 ,
.Xr err 3 ,
.Xr sysctlbyname 3 ,
.Xr capsicum 4 ,
.Xr nv 9
.Sh AUTHORS
The
.Nm cap_sysctl
service was implemented by
.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net
under sponsorship from the FreeBSD Foundation.
.Pp
This manual page was written by
.An Mariusz Zaborski Aq Mt oshogbo@FreeBSD.org .