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freebsd/lib/libc/sys/cap_enter.2
Enji Cooper 60f14b3186 cap_enter(2): fix manlint issues
- Sort SEE ALSO section appropriately.
- Correct section for sysctl(9).

Reported by:	make manlint
MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon
2017-05-23 07:31:03 +00:00

161 lines
4.7 KiB
Groff

.\"
.\" Copyright (c) 2008-2009 Robert N. M. Watson
.\" All rights reserved.
.\"
.\" This software was developed at the University of Cambridge Computer
.\" Laboratory with support from a grant from Google, Inc.
.\"
.\" 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.
.\"
.\" $FreeBSD$
.\"
.Dd May 23, 2017
.Dt CAP_ENTER 2
.Os
.Sh NAME
.Nm cap_enter ,
.Nm cap_getmode
.Nd Capability mode system calls
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/capsicum.h
.Ft int
.Fn cap_enter "void"
.Ft int
.Fn cap_getmode "u_int *modep"
.Sh DESCRIPTION
.Fn cap_enter
places the current process into capability mode, a mode of execution in which
processes may only issue system calls operating on file descriptors or
reading limited global system state.
Access to global name spaces, such as file system or IPC name spaces, is
prevented.
If the process is already in a capability mode sandbox, the system call is a
no-op.
Future process descendants created with
.Xr fork 2
or
.Xr pdfork 2
will be placed in capability mode from inception.
.Pp
When combined with
.Xr cap_rights_limit 2 ,
.Xr cap_ioctls_limit 2 ,
.Xr cap_fcntls_limit 2 ,
.Fn cap_enter
may be used to create kernel-enforced sandboxes in which
appropriately-crafted applications or application components may be run.
.Pp
.Fn cap_getmode
returns a flag indicating whether or not the process is in a capability mode
sandbox.
.Sh RUN-TIME SETTINGS
If the
.Dv kern.trap_enotcap
sysctl MIB is set to a non-zero value, then for any process executing in a
capability mode sandbox, any syscall which results in either an
.Er ENOTCAPABLE
or
.Er ECAPMODE
error also generates the synchronous
.Dv SIGTRAP
signal to the thread on the syscall return.
On signal delivery, the
.Va si_errno
member of the
.Fa siginfo
signal handler parameter is set to the syscall error value,
and the
.Va si_code
member is set to
.Dv TRAP_CAP .
.Pp
See also the
.Dv PROC_TRAPCAP_CTL
and
.Dv PROC_TRAPCAP_STATUS
operations of the
.Xr procctl 2
function for similar per-process functionality.
.Sh CAVEAT
Creating effective process sandboxes is a tricky process that involves
identifying the least possible rights required by the process and then
passing those rights into the process in a safe manner.
Consumers of
.Fn cap_enter
should also be aware of other inherited rights, such as access to VM
resources, memory contents, and other process properties that should be
considered.
It is advisable to use
.Xr fexecve 2
to create a runtime environment inside the sandbox that has as few implicitly
acquired rights as possible.
.Sh RETURN VALUES
.Rv -std cap_enter cap_getmode
.Pp
When the process is in capability mode,
.Fn cap_getmode
sets the flag to a non-zero value.
A zero value means the process is not in capability mode.
.Sh ERRORS
The
.Fn cap_enter
and
.Fn cap_getmode
system calls
will fail if:
.Bl -tag -width Er
.It Bq Er ENOSYS
The kernel is compiled without:
.Pp
.Cd "options CAPABILITY_MODE"
.El
.Pp
The
.Fn cap_getmode
system call may also return the following error:
.Bl -tag -width Er
.It Bq Er EFAULT
Pointer
.Fa modep
points outside the process's allocated address space.
.El
.Sh SEE ALSO
.Xr cap_fcntls_limit 2 ,
.Xr cap_ioctls_limit 2 ,
.Xr cap_rights_limit 2 ,
.Xr fexecve 2 ,
.Xr procctl 2 ,
.Xr cap_sandboxed 3 ,
.Xr capsicum 4 ,
.Xr sysctl 9
.Sh HISTORY
Support for capabilities and capabilities mode was developed as part of the
.Tn TrustedBSD
Project.
.Sh AUTHORS
These functions and the capability facility were created by
.An "Robert N. M. Watson"
at the University of Cambridge Computer Laboratory with support from a grant
from Google, Inc.