.\" Copyright (c) 2018 Mariusz Zaborski .\" 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 May 13, 2019 .Dt CAP_SYSCTL 3 .Os .Sh NAME .Nm cap_sysctl .Nd "library for getting or setting system information in capability mode" .Sh LIBRARY .Lb libcap_sysctl .Sh SYNOPSIS .In libcasper.h .In casper/cap_sysctl.h .Ft int .Fn cap_sysctl "cap_channel_t *chan" "const int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen" .Ft int .Fn cap_sysctlbyname "cap_channel_t *chan" "const char *name" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen" .Ft int .Fn cap_sysctlnametomib "cap_channel_t *chan" "const char *name" "int *mibp" "size_t *sizep" .Ft void * .Fn cap_sysctl_limit_init "cap_channel_t *chan" .Ft void * .Fn cap_sysctl_limit_name "void *limit" "const char *name" "int flags" .Ft void * .Fn cap_sysctl_limit_mib "void *limit" "int *mibp" "u_int miblen" "int flags" .Ft int .Fn cap_sysctl_limit "void *limit" .Sh DESCRIPTION The .Fn cap_sysctl , .Fn cap_sysctlbyname and .Fn cap_sysctlnametomib functions are equivalent to .Xr sysctl 3 , .Xr sysctlbyname 3 and .Xr sysctlnametomib 3 , except that they are implemented by the .Ql system.sysctl .Xr libcasper 3 service and require a corresponding .Xr libcasper 3 capability. .Sh LIMITS By default, the .Nm capability provides unrestricted access to the sysctl namespace. Applications typically only require access to a small number of sysctl variables; the .Fn cap_sysctl_limit interface can be used to restrict the sysctls that can be accessed using the .Nm capability. .Fn cap_sysctl_limit_init returns an opaque limit handle used to store a list of permitted sysctls and access rights. Rights are encoded using the following flags: .Pp .Bd -literal -offset indent -compact CAP_SYSCTL_READ allow reads of the sysctl variable CAP_SYSCTL_WRITE allow writes of the sysctl variable CAP_SYSCTL_RDWR allow reads and writes of the sysctl variable CAP_RECURSIVE permit access to any child of the sysctl variable .Ed .Pp The .Fn cap_sysctl_limit_name function adds the sysctl identified by .Ar name to the limit list, and .Fn cap_sysctl_limit_mib function adds the sysctl identified by .Ar mibp to the limit list. The access rights for the sysctl are specified in the .Ar flags parameter; at least one of .Dv CAP_SYSCTL_READ , .Dv CAP_SYSCTL_WRITE and .Dv CAP_SYSCTL_RDWR must be specified. .Fn cap_sysctl_limit applies a set of sysctl limits to the capability, denying access to sysctl variables not belonging to the set. .Pp Once a set of limits is applied, subsequent calls to .Fn cap_sysctl_limit will fail unless the new set is a subset of the current set. .Pp .Fn cap_sysctlnametomib will succeed so long as the named sysctl variable is present in the limit set, regardless of its access rights. When a sysctl variable name is added to a limit set, its MIB identifier is automatically added to the set. .Sh EXAMPLES The following example first opens a capability to casper, uses this capability to create the .Nm system.sysctl casper service, and then uses the .Nm capability to get the value of .Dv kern.trap_enotcap . .Bd -literal cap_channel_t *capcas, *capsysctl; const char *name = "kern.trap_enotcap"; void *limit; 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. */ limit = cap_sysctl_limit_init(capsysctl); (void)cap_sysctl_limit_name(limit, name, CAP_SYSCTL_READ); /* Limit system.sysctl. */ if (cap_sysctl_limit(limit) < 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 sysctl 3 , .Xr sysctlbyname 3 , .Xr sysctlnametomib 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 .