1.\" 2.\" Copyright (c) 2008-2010 Robert N. M. Watson 3.\" Copyright (c) 2012-2013 The FreeBSD Foundation 4.\" All rights reserved. 5.\" 6.\" This software was developed at the University of Cambridge Computer 7.\" Laboratory with support from a grant from Google, Inc. 8.\" 9.\" Portions of this documentation were written by Pawel Jakub Dawidek 10.\" under sponsorship from the FreeBSD Foundation. 11.\" 12.\" Redistribution and use in source and binary forms, with or without 13.\" modification, are permitted provided that the following conditions 14.\" are met: 15.\" 1. Redistributions of source code must retain the above copyright 16.\" notice, this list of conditions and the following disclaimer. 17.\" 2. Redistributions in binary form must reproduce the above copyright 18.\" notice, this list of conditions and the following disclaimer in the 19.\" documentation and/or other materials provided with the distribution. 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 22.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 25.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31.\" SUCH DAMAGE. 32.\" 33.Dd March 9, 2023 34.Dt CAP_RIGHTS_LIMIT 2 35.Os 36.Sh NAME 37.Nm cap_rights_limit 38.Nd limit capability rights 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/capsicum.h 43.Ft int 44.Fn cap_rights_limit "int fd" "const cap_rights_t *rights" 45.Sh DESCRIPTION 46When a file descriptor is created by a function such as 47.Xr accept 2 , 48.Xr accept4 2 , 49.Xr fhopen 2 , 50.Xr kqueue 2 , 51.Xr mq_open 2 , 52.Xr open 2 , 53.Xr openat 2 , 54.Xr pdfork 2 , 55.Xr pipe 2 , 56.Xr shm_open 2 , 57.Xr socket 2 58or 59.Xr socketpair 2 , 60it is assigned all capability rights. 61Those rights can be reduced (but never expanded) by using the 62.Fn cap_rights_limit 63system call. 64Once capability rights are reduced, operations on the file descriptor will be 65limited to those permitted by 66.Fa rights . 67.Pp 68The 69.Fa rights 70argument should be prepared using 71.Xr cap_rights_init 3 72family of functions. 73.Pp 74Capability rights assigned to a file descriptor can be obtained with the 75.Xr cap_rights_get 3 76function. 77.Pp 78The complete list of the capability rights can be found in the 79.Xr rights 4 80manual page. 81.Sh RETURN VALUES 82.Rv -std 83.Sh EXAMPLES 84The following example demonstrates how to limit file descriptor capability 85rights to allow reading only. 86.Bd -literal 87cap_rights_t setrights; 88char buf[1]; 89int fd; 90 91fd = open("/tmp/foo", O_RDWR); 92if (fd < 0) 93 err(1, "open() failed"); 94 95if (cap_enter() < 0) 96 err(1, "cap_enter() failed"); 97 98cap_rights_init(&setrights, CAP_READ); 99if (cap_rights_limit(fd, &setrights) < 0) 100 err(1, "cap_rights_limit() failed"); 101 102buf[0] = 'X'; 103 104if (write(fd, buf, sizeof(buf)) > 0) 105 errx(1, "write() succeeded!"); 106 107if (read(fd, buf, sizeof(buf)) < 0) 108 err(1, "read() failed"); 109.Ed 110.Sh ERRORS 111.Fn cap_rights_limit 112succeeds unless: 113.Bl -tag -width Er 114.It Bq Er EBADF 115The 116.Fa fd 117argument is not a valid active descriptor. 118.It Bq Er EINVAL 119An invalid right has been requested in 120.Fa rights . 121.It Bq Er ENOSYS 122The running kernel was compiled without 123.Cd "options CAPABILITY_MODE" . 124.It Bq Er ENOTCAPABLE 125The 126.Fa rights 127argument contains capability rights not present for the given file descriptor. 128Capability rights list can only be reduced, never expanded. 129.El 130.Sh SEE ALSO 131.Xr accept 2 , 132.Xr accept4 2 , 133.Xr cap_enter 2 , 134.Xr fhopen 2 , 135.Xr kqueue 2 , 136.Xr mq_open 2 , 137.Xr open 2 , 138.Xr openat 2 , 139.Xr pdfork 2 , 140.Xr pipe 2 , 141.Xr read 2 , 142.Xr shm_open 2 , 143.Xr socket 2 , 144.Xr socketpair 2 , 145.Xr write 2 , 146.Xr cap_rights_get 3 , 147.Xr cap_rights_init 3 , 148.Xr err 3 , 149.Xr capsicum 4 , 150.Xr rights 4 151.Sh HISTORY 152The 153.Fn cap_rights_limit 154function first appeared in 155.Fx 8.3 . 156Support for capabilities and capabilities mode was developed as part of the 157.Tn TrustedBSD 158Project. 159.Sh AUTHORS 160This function was created by 161.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net 162under sponsorship of the FreeBSD Foundation. 163