1.\" 2.\" Copyright (c) 2011, 2013 Robert N. M. Watson 3.\" Copyright (c) 2011 Jonathan Anderson 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" $FreeBSD$ 28.\" 29.Dd April 19, 2022 30.Dt CAPSICUM 4 31.Os 32.Sh NAME 33.Nm Capsicum 34.Nd lightweight OS capability and sandbox framework 35.Sh SYNOPSIS 36.Cd "options CAPABILITY_MODE" 37.Cd "options CAPABILITIES" 38.Sh DESCRIPTION 39.Nm 40is a lightweight OS capability and sandbox framework implementing a hybrid 41capability system model. 42Capabilities are unforgeable tokens of authority that can be delegated and must 43be presented to perform an action. 44.Nm 45makes file descriptors into capabilities. 46.Pp 47.Nm 48can be used for application and library compartmentalisation, the 49decomposition of larger bodies of software into isolated (sandboxed) 50components in order to implement security policies and limit the impact of 51software vulnerabilities. 52.Pp 53.Nm 54provides two core kernel primitives: 55.Bl -tag -width indent 56.It capability mode 57A process mode, entered by invoking 58.Xr cap_enter 2 , 59in which access to global OS namespaces (such as the file system and PID 60namespaces) is restricted; only explicitly delegated rights, referenced by 61memory mappings or file descriptors, may be used. 62Once set, the flag is inherited by future children processes, and may not be 63cleared. 64.It capabilities 65Limit operations that can be called on file descriptors. 66For example, a file descriptor returned by 67.Xr open 2 68may be refined using 69.Xr cap_rights_limit 2 70so that only 71.Xr read 2 72and 73.Xr write 2 74can be called, but not 75.Xr fchmod 2 . 76The complete list of the capability rights can be found in the 77.Xr rights 4 78manual page. 79.El 80.Pp 81In some cases, 82.Nm 83requires use of alternatives to traditional POSIX APIs in order to name 84objects using capabilities rather than global namespaces: 85.Bl -tag -width indent 86.It process descriptors 87File descriptors representing processes, allowing parent processes to manage 88child processes without requiring access to the PID namespace; described in 89greater detail in 90.Xr procdesc 4 . 91.It anonymous shared memory 92An extension to the POSIX shared memory API to support anonymous swap objects 93associated with file descriptors; described in greater detail in 94.Xr shm_open 2 . 95.El 96.Pp 97In some cases, 98.Nm 99limits the valid values of some parameters to traditional APIs in order to 100restrict access to global namespaces: 101.Bl -tag -width indent 102.It process IDs 103Processes can only act upon their own process ID with syscalls such as 104.Xr cpuset_setaffinity 2 . 105.El 106.Sh SEE ALSO 107.Xr cap_enter 2 , 108.Xr cap_fcntls_limit 2 , 109.Xr cap_getmode 2 , 110.Xr cap_ioctls_limit 2 , 111.Xr cap_rights_limit 2 , 112.Xr fchmod 2 , 113.Xr open 2 , 114.Xr pdfork 2 , 115.Xr pdgetpid 2 , 116.Xr pdkill 2 , 117.Xr pdwait4 2 , 118.Xr read 2 , 119.Xr shm_open 2 , 120.Xr write 2 , 121.Xr cap_rights_get 3 , 122.Xr libcasper 3 , 123.Xr procdesc 4 124.Sh HISTORY 125.Nm 126first appeared in 127.Fx 9.0 , 128and was developed at the University of Cambridge. 129.Sh AUTHORS 130.Nm 131was developed by 132.An -nosplit 133.An Robert Watson Aq Mt rwatson@FreeBSD.org 134and 135.An Jonathan Anderson Aq Mt jonathan@FreeBSD.org 136at the University of Cambridge, and 137.An Ben Laurie Aq Mt benl@FreeBSD.org 138and 139.An Kris Kennaway Aq Mt kris@FreeBSD.org 140at Google, Inc., and 141.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net . 142