tail head cat sleep
QR code linking to this page

Manual Pages  — CAP_RIGHTS_LIMIT


cap_rights_limit – limit capability rights



Standard C Library (libc, -lc)


#include <sys/capsicum.h>

cap_rights_limit(int fd, const cap_rights_t *rights);


When a file descriptor is created by a function such as accept(2), accept4(2), fhopen(2), kqueue(2), mq_open(2), open(2), openat(2), pdfork(2), pipe(2), shm_open(2), socket(2) or socketpair(2), it is assigned all capability rights. Those rights can be reduced (but never expanded) by using the cap_rights_limit() system call. Once capability rights are reduced, operations on the file descriptor will be limited to those permitted by rights.

The rights argument should be prepared using cap_rights_init(3) family of functions.

Capability rights assigned to a file descriptor can be obtained with the cap_rights_get(3) function.

The complete list of the capability rights can be found in the rights(4) manual page.


Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.


The following example demonstrates how to limit file descriptor capability rights to allow reading only.
cap_rights_t setrights;
char buf[1];
int fd;

fd = open("/tmp/foo", O_RDWR); if (fd < 0)         err(1, "open() failed");

if (cap_enter() < 0)         err(1, "cap_enter() failed");

cap_rights_init(&setrights, CAP_READ); if (cap_rights_limit(fd, &setrights) < 0)         err(1, "cap_rights_limit() failed");

buf[0] = 'X';

if (write(fd, buf, sizeof(buf)) > 0)         errx(1, "write() succeeded!");

if (read(fd, buf, sizeof(buf)) < 0)         err(1, "read() failed");


cap_rights_limit() succeeds unless:
  The fd argument is not a valid active descriptor.
  An invalid right has been requested in rights.
  The rights argument contains capability rights not present for the given file descriptor. Capability rights list can only be reduced, never expanded.


accept(2), accept4(2), cap_enter(2), fhopen(2), kqueue(2), mq_open(2), open(2), openat(2), pdfork(2), pipe(2), read(2), shm_open(2), socket(2), socketpair(2), write(2), cap_rights_get(3), cap_rights_init(3), err(3), capsicum(4), rights(4)


Support for capabilities and capabilities mode was developed as part of the TrustedBSD Project.


This function was created by Pawel Jakub Dawidek <Mt pawel@dawidek.net> under sponsorship of the FreeBSD Foundation.

CAP_RIGHTS_LIMIT (2) March 27, 2014

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

C is a language that combines all the elegance and power of assembly language with all the readability and maintainability of assembly language.