Scroll to navigation

CAP_RIGHTS_LIMIT(2) System Calls Manual CAP_RIGHTS_LIMIT(2)

NAME

cap_rights_limit —
limit capability rights

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/capability.h>
int
cap_rights_limit(int fd, const cap_rights_t *rights);

DESCRIPTION

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.

RETURN VALUES

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.

EXAMPLES

The following example demonstrates how to limit file descriptor capability rights to allow reading only. 
cap_rights_t rights; 
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");

ERRORS

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.

SEE ALSO

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)

HISTORY

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

AUTHORS

This function was created by Pawel Jakub Dawidek ⟨pawel@dawidek.net⟩ under sponsorship of the FreeBSD Foundation.
February 23, 2013 Debian