1.\" 2.\" Copyright (c) 2008-2009 Robert N. M. Watson 3.\" All rights reserved. 4.\" 5.\" This software was developed at the University of Cambridge Computer 6.\" Laboratory with support from a grant from Google, Inc. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd February 25, 2012 32.Dt CAP_ENTER 2 33.Os 34.Sh NAME 35.Nm cap_enter , 36.Nm cap_getmode 37.Nd Capability mode system calls 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/capability.h 42.Ft int 43.Fn cap_enter "void" 44.Ft int 45.Fn cap_getmode "u_int *modep" 46.Sh DESCRIPTION 47.Fn cap_enter 48places the current process into capability mode, a mode of execution in which 49processes may only issue system calls operating on file descriptors or 50reading limited global system state. 51Access to global name spaces, such as file system or IPC name spaces, is 52prevented. 53If the process is already in a capability mode sandbox, the system call is a 54no-op. 55Future process descendants create with 56.Xr fork 2 57or 58.Xr pdfork 2 59will be placed in capability mode from inception. 60.Pp 61When combined with capabilities created with 62.Xr cap_new 2 , 63.Fn cap_enter 64may be used to create kernel-enforced sandboxes in which 65appropriately-crafted applications or application components may be run. 66.Pp 67.Fn cap_getmode 68returns a flag indicating whether or not the process is in a capability mode 69sandbox. 70.Sh CAVEAT 71Creating effective process sandboxes is a tricky process that involves 72identifying the least possible rights required by the process and then 73passing those rights into the process in a safe manner. 74See the CAVEAT 75section of 76.Xr cap_new 2 77for why this is particularly tricky with UNIX file descriptors as the 78canonical representation of a right. 79Consumers of 80.Fn cap_enter 81should also be aware of other inherited rights, such as access to VM 82resources, memory contents, and other process properties that should be 83considered. 84It is advisable to use 85.Xr fexecve 2 86to create a runtime environment inside the sandbox that has as few implicitly 87acquired rights as possible. 88.Sh RETURN VALUES 89.Rv -std cap_enter cap_getmode 90.Sh SEE ALSO 91.Xr cap_new 2 , 92.Xr fexecve 2 , 93.Xr capsicum 4 94.Sh HISTORY 95Support for capabilities and capabilities mode was developed as part of the 96.Tn TrustedBSD 97Project. 98.Sh AUTHORS 99These functions and the capability facility were created by 100.An "Robert N. M. Watson" 101at the University of Cambridge Computer Laboratory with support from a grant 102from Google, Inc. 103