20daf0ca6e
The CAVEATS section was misspelled as "CAVEAT" before this change. Fix the spelling to identify issues related to the section. Furthermore, given that the section order was incorrect, move the CAVEATS section down to the bottom of the manpage, per the conventional section order. MFC after: 1 week Reported by: make manlint Sponsored by: DellEMC Isilon
165 lines
4.8 KiB
Groff
165 lines
4.8 KiB
Groff
.\"
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.\" Copyright (c) 2008-2009 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" This software was developed at the University of Cambridge Computer
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.\" Laboratory with support from a grant from Google, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 5, 2020
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.Dt CAP_ENTER 2
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.Os
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.Sh NAME
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.Nm cap_enter ,
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.Nm cap_getmode
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.Nd Capability mode system calls
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/capsicum.h
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.Ft int
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.Fn cap_enter "void"
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.Ft int
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.Fn cap_getmode "u_int *modep"
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.Sh DESCRIPTION
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.Fn cap_enter
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places the current process into capability mode, a mode of execution in which
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processes may only issue system calls operating on file descriptors or
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reading limited global system state.
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Access to global name spaces, such as file system or IPC name spaces, is
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prevented.
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If the process is already in a capability mode sandbox, the system call is a
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no-op.
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Future process descendants created with
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.Xr fork 2
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or
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.Xr pdfork 2
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will be placed in capability mode from inception.
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.Pp
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When combined with
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.Xr cap_rights_limit 2 ,
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.Xr cap_ioctls_limit 2 ,
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.Xr cap_fcntls_limit 2 ,
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.Fn cap_enter
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may be used to create kernel-enforced sandboxes in which
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appropriately-crafted applications or application components may be run.
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.Pp
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.Fn cap_getmode
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returns a flag indicating whether or not the process is in a capability mode
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sandbox.
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.Sh RUN-TIME SETTINGS
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If the
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.Dv kern.trap_enotcap
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sysctl MIB is set to a non-zero value, then for any process executing in a
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capability mode sandbox, any syscall which results in either an
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.Er ENOTCAPABLE
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or
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.Er ECAPMODE
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error also generates the synchronous
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.Dv SIGTRAP
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signal to the thread on the syscall return.
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On signal delivery, the
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.Va si_errno
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member of the
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.Fa siginfo
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signal handler parameter is set to the syscall error value,
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and the
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.Va si_code
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member is set to
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.Dv TRAP_CAP .
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.Pp
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See also the
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.Dv PROC_TRAPCAP_CTL
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and
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.Dv PROC_TRAPCAP_STATUS
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operations of the
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.Xr procctl 2
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function for similar per-process functionality.
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.Sh RETURN VALUES
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.Rv -std cap_enter cap_getmode
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.Pp
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When the process is in capability mode,
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.Fn cap_getmode
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sets the flag to a non-zero value.
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A zero value means the process is not in capability mode.
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.Sh ERRORS
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The
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.Fn cap_enter
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and
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.Fn cap_getmode
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er ENOSYS
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The kernel is compiled without:
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.Pp
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.Cd "options CAPABILITY_MODE"
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.El
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.Pp
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The
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.Fn cap_getmode
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system call may also return the following error:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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Pointer
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.Fa modep
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points outside the process's allocated address space.
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.El
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.Sh SEE ALSO
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.Xr cap_fcntls_limit 2 ,
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.Xr cap_ioctls_limit 2 ,
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.Xr cap_rights_limit 2 ,
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.Xr fexecve 2 ,
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.Xr procctl 2 ,
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.Xr cap_sandboxed 3 ,
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.Xr capsicum 4 ,
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.Xr sysctl 9
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.Sh HISTORY
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The
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.Fn cap_getmode
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system call first appeared in
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.Fx 8.3 .
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Support for capabilities and capabilities mode was developed as part of the
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.Tn TrustedBSD
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Project.
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.Sh AUTHORS
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These functions and the capability facility were created by
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.An "Robert N. M. Watson"
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at the University of Cambridge Computer Laboratory with support from a grant
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from Google, Inc.
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.Sh CAVEATS
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Creating effective process sandboxes is a tricky process that involves
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identifying the least possible rights required by the process and then
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passing those rights into the process in a safe manner.
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Consumers of
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.Fn cap_enter
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should also be aware of other inherited rights, such as access to VM
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resources, memory contents, and other process properties that should be
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considered.
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It is advisable to use
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.Xr fexecve 2
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to create a runtime environment inside the sandbox that has as few implicitly
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acquired rights as possible.
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