476 lines
11 KiB
Groff
476 lines
11 KiB
Groff
.\"
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.\" Copyright (c) 2008-2010 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 July 20, 2011
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.Dt CAP_NEW 2
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.Os
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.Sh NAME
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.Nm cap_new ,
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.Nm cap_getrights
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.Nd System calls to manipulate capabilities
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/capability.h
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.Ft int
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.Fn cap_new "int fd" "cap_rights_t rights"
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.Ft int
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.Fn cap_getrights "int fd" "cap_rights_t *rightsp"
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.Sh DESCRIPTION
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Capabilities are special file descriptors derived from an existing file
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descriptor, such as one returned by
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.Xr fhopen 2 ,
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.Xr kqueue 2 ,
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.Xr mq_open 2 ,
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.Xr open 2 ,
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.Xr pipe 2 ,
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.Xr shm_open 2 ,
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.Xr socket 2 ,
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or
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.Xr socketpair 2 ,
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but with a restricted set of permitted operations determined by a rights
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mask set when the capability is created.
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These restricted rights cannot be changed after the capability is created,
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although further capabilities with yet more restricted rights may be created
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from an existing capability.
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In every other sense, a capability behaves in the same way as the file
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descriptor it was created from.
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.Pp
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.Fn cap_new
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creates a new capability for the existing file descriptor
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.Fa fd ,
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and returns a file descriptor for it.
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Operations on the capability will be limited to those permitted by
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.Fa rights ,
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which is static for the lifetime of the capability.
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If
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.Fa fd
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refers to an existing capability, then
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.Fa rights
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must be equal to or a subset of the rights on that capability.
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As with
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.Xr dup 2
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and
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.Xr dup2 2 ,
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many properties are shared between the new capability and the existing file
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descriptor, including open file flags, blocking disposition, and file offset.
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Many applications will prefer to use the
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.Xr cap_limitfd 3
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library call, part of
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.Xr libcapsicum 3 ,
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as it offers a more convenient interface.
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.Pp
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.Fn cap_getrights
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queries the rights associated with the capability referred to by file
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descriptor
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.Fa fd .
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.Pp
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These system calls, when combined with
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.Xr cap_enter 2 ,
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may be used to construct process sandboxes with highly granular rights
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assignment.
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.Sh RIGHTS
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The following rights may be specified in a new capability rights mask:
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.Bl -tag -width CAP_EXTATTR_DELETE
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.It Dv CAP_ACCEPT
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Permit
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.Xr accept 2 .
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.It Dv CAP_ACL_CHECK
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Permit checking of an ACL on a file descriptor; there is no cross-reference
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for this system call.
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.It Dv CAP_ACL_DELETE
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Permit
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.Xr acl_delete_fd_np 3 .
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.It Dv CAP_ACL_GET
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Permit
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.Xr acl_get_fd 3
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and
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.Xr acl_get_fd_np 3 .
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.It Dv CAP_ACL_SET
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Permit
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.Xr acl_set_fd 3
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and
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.Xr acl_set_fd_np 3 .
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.It Dv CAP_BIND
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Permit
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.Xr bind 2 .
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Note that sockets can also become bound implicitly as a result of
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.Xr connect 2
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or
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.Xr send 2 ,
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and that socket options set with
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.Xr setsockopt 2
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may also affect binding behavior.
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.It Dv CAP_CONNECT
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Permit
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.Xr connect 2 ;
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also required for
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.Xr sendto 2
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with a non-NULL destination address.
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.It Dv CAP_EVENT
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Permit
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.Xr select 2 ,
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.Xr poll 2 ,
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and
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.Xr kevent 2
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to be used in monitoring the file descriptor for events.
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.It Dv CAP_FEXECVE
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Permit
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.Xr fexecve 2 ;
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.Dv CAP_READ
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will also be required.
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.It Dv CAP_EXTATTR_DELETE
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Permit
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.Xr extattr_delete_fd 2 .
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.It Dv CAP_EXTATTR_GET
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Permit
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.Xr extattr_get_fd 2 .
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.It Dv CAP_EXTATTR_LIST
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Permit
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.Xr extattr_list_fd 2 .
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.It Dv CAP_EXTATTR_SET
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Permit
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.Xr extattr_set_fd 2 .
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.It Dv CAP_FCHDIR
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Permit
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.Xr fchdir 2 .
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.It Dv CAP_FCHFLAGS
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Permit
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.Xr fchflags 2 .
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.It Dv CAP_FCHMOD
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Permit
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.Xr fchmod 2 .
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.It Dv CAP_FCHOWN
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Permit
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.Xr fchown 2 .
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.It Dv CAP_FCNTL
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Permit
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.Xr fcntl 2 ;
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be aware that this call provides indirect access to other operations, such as
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.Xr flock 2 .
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.It Dv CAP_FLOCK
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Permit
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.Xr flock 2
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and related calls.
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.It Dv CAP_FPATHCONF
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Permit
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.Xr fpathconf 2 .
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.It Dv CAP_FSCK
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Permit UFS background-fsck operations on the descriptor.
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.It Dv CAP_FSTAT
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Permit
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.Xr fstat 2 .
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.It Dv CAP_FSTATFS
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Permit
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.Xr fstatfs 2 .
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.It Dv CAP_FSYNC
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Permit
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.Xr aio_fsync 2
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and
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.Xr fsync 2 .
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.Pp
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.It Dv CAP_FTRUNCATE
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Permit
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.Xr ftruncate 2 .
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.It Dv CAP_FUTIMES
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Permit
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.Xr futimes 2 .
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.It Dv CAP_GETPEERNAME
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Permit
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.Xr getpeername 2 .
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.It Dv CAP_GETSOCKNAME
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Permit
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.Xr getsockname 2 .
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.It Dv CAP_GETSOCKOPT
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Permit
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.Xr getsockopt 2 .
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.It Dv CAP_IOCTL
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Permit
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.Xr ioctl 2 .
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Be aware that this system call has enormous scope, including potentially
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global scope for some objects.
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.It Dv CAP_KEVENT
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Permit
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.Xr kevent 2 ;
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.Dv CAP_EVENT
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is also required on file descriptors that will be monitored using
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.Xr kevent 2 .
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.It Dv CAP_LISTEN
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Permit
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.Xr listen 2 ;
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not much use (generally) without
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.Dv CAP_BIND .
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.It Dv CAP_LOOKUP
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Permit the file descriptor to be used as a starting directory for calls such
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as
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.Xr linkat 2 ,
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.Xr openat 2 ,
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and
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.Xr unlinkat 2 .
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Note that these calls are not available in capability mode as they manipulate
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a global name space; see
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.Xr cap_enter 2
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for details.
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.It Dv CAP_MAC_GET
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Permit
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.Xr mac_get_fd 3 .
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.It Dv CAP_MAC_SET
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Permit
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.Xr mac_set_fd 3 .
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.It Dv CAP_MMAP
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Permit
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.Xr mmap 2 ;
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specific invocations may also require
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.Dv CAP_READ
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or
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.Dv CAP_WRITE .
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.Pp
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.It Dv CAP_PDGETPID
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Permit
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.Xr pdgetpid 2 .
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.It Dv CAP_PDKILL
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Permit
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.Xr pdkill 2 .
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.It Dv CAP_PDWAIT
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Permit
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.Xr pdwait4 2 .
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.It Dv CAP_PEELOFF
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Permit
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.Xr sctp_peeloff 2 .
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.It Dv CAP_READ
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Allow
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.Xr aio_read 2 ,
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.Xr pread 2 ,
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.Xr read 2 ,
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.Xr recv 2 ,
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.Xr recvfrom 2 ,
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.Xr recvmsg 2 ,
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and related system calls.
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.Pp
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For files and other seekable objects,
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.Dv CAP_SEEK
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may also be required.
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.It Dv CAP_REVOKE
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Permit
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.Xr frevoke 2
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in certain ABI compatibility modes that support this system call.
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.It Dv CAP_SEEK
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Permit operations that seek on the file descriptor, such as
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.Xr lseek 2 ,
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but also required for I/O system calls that modify the file offset, such as
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.Xr read 2
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and
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.Xr write 2 .
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.It Dv CAP_SEM_GETVALUE
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Permit
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.Xr sem_getvalue 3 .
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.It Dv CAP_SEM_POST
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Permit
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.Xr sem_post 3 .
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.It Dv CAP_SEM_WAIT
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Permit
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.Xr sem_wait 3
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and
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.Xr sem_trywait 3 .
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.It Dv CAP_SETSOCKOPT
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Permit
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.Xr setsockopt 2 ;
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this controls various aspects of socket behavior and may affect binding,
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connecting, and other behaviors with global scope.
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.It Dv CAP_SHUTDOWN
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Permit explicit
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.Xr shutdown 2 ;
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closing the socket will also generally shut down any connections on it.
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.It Dv CAP_TTYHOOK
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Allow configuration of TTY hooks, such as
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.Xr snp 4 ,
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on the file descriptor.
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.It Dv CAP_WRITE
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Allow
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.Xr aio_write 2 ,
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.Xr pwrite 2 ,
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.Xr send 2 ,
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.Xr sendmsg 2 ,
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.Xr sendto 2 ,
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.Xr write 2 ,
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and related system calls.
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.Pp
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For files and other seekable objects,
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.Dv CAP_SEEK
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may also be required.
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.Pp
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For
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.Xr sendto 2
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with a non-NULL connection address,
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.Dv CAP_CONNECT
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is also required.
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.El
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.Sh CAVEAT
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The
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.Fn cap_new
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system call and the capabilities it creates may be used to assign
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fine-grained rights to sandboxed processes running in capability mode.
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However, the semantics of objects accessed via file descriptors are complex,
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so caution should be exercised in passing object capabilities into sandboxes.
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.Sh RETURN VALUES
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If successful,
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.Fn cap_new
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returns a non-negative integer, termed a file descriptor.
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It returns -1 on failure, and sets
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.Va errno
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to indicate the error.
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.Pp
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.Rv -std cap_getrights
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.Sh ERRORS
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.Fn cap_new
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may return the following errors:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument is not a valid active descriptor.
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.It Bq Er EINVAL
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An invalid right has been requested in
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.Fa rights .
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.It Bq Er EMFILE
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The process has already reached its limit for open file descriptors.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er EPERM
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.Fa rights
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contains requested rights not present in the current rights mask associated
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with the capability referenced by
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.Fa fd ,
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if any.
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.El
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.Pp
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.Fn cap_getrights
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may return the following errors:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument is not a valid active descriptor.
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.It Bq Er EINVAL
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The
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.Fa fd
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argument is not a capability.
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr aio_fsync 2 ,
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.Xr aio_read 2 ,
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.Xr aio_write 2 ,
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.Xr bind 2 ,
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.Xr cap_enter 2 ,
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.Xr connect 2 ,
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.Xr dup 2 ,
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.Xr dup2 2 ,
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.Xr extattr_delete_fd 2 ,
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.Xr extattr_get_fd 2 ,
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.Xr extattr_list_fd 2 ,
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.Xr extattr_set_fd 2 ,
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.Xr fchflags 2 ,
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.Xr fchown 2 ,
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.Xr fcntl 2 ,
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.Xr fexecve 2 ,
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.Xr fhopen 2 ,
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.Xr flock 2 ,
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.Xr fpathconf 2 ,
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.Xr fstat 2 ,
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.Xr fstatfs 2 ,
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.Xr fsync 2 ,
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.Xr ftruncate 2 ,
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.Xr futimes 2 ,
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.Xr getpeername 2 ,
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.Xr getsockname 2 ,
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.Xr getsockopt 2 ,
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.Xr ioctl 2 ,
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.Xr kevent 2 ,
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.Xr kqueue 2 ,
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.Xr linkat 2 ,
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.Xr listen 2 ,
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.Xr mmap 2 ,
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.Xr mq_open 2 ,
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.Xr open 2 ,
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.Xr openat 2 ,
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.Xr pdgetpid 2 ,
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.Xr pdkill 2 ,
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.Xr pdwait4 2 ,
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.Xr pipe 2 ,
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.Xr poll 2 ,
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.Xr pread 2 ,
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.Xr pwrite 2 ,
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.Xr read 2 ,
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.Xr recv 2 ,
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.Xr recvfrom 2 ,
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.Xr recvmsg 2 ,
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.Xr sctp_peeloff 2 ,
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.Xr select 2 ,
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.Xr send 2 ,
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.Xr sendmsg 2 ,
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.Xr sendto 2 ,
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.Xr setsockopt 2 ,
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.Xr shm_open 2 ,
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.Xr shutdown 2 ,
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.Xr socket 2 ,
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.Xr socketpair 2 ,
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.Xr unlinkat 2 ,
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.Xr write 2 ,
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.Xr acl_delete_fd_np 3 ,
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.Xr acl_get_fd 3 ,
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.Xr acl_get_fd_np 3 ,
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.Xr acl_set_fd_np 3 ,
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.Xr cap_limitfd 3 ,
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.Xr libcapsicum 3 ,
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.Xr mac_get_fd 3 ,
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.Xr mac_set_fd 3 ,
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.Xr sem_getvalue 3 ,
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.Xr sem_post 3 ,
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.Xr sem_trywait 3 ,
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.Xr sem_wait 3 ,
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.Xr capsicum 4 ,
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.Xr snp 4
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.Sh HISTORY
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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 BUGS
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This man page should list the set of permitted system calls more specifically
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for each capability right.
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.Pp
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Capability rights sometimes have unclear indirect impacts, which should be
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documented, or at least hinted at.
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