CAP_RIGHTS_LIMIT(2)					      BSD System Calls Manual					       CAP_RIGHTS_LIMIT(2)

NAME

     cap_rights_limit -- limit capability rights

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/capsicum.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 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");

ERRORS

     cap_rights_limit() succeeds unless:

     [EBADF]		The fd argument is not a valid active descriptor.

     [EINVAL]		An invalid right has been requested in rights.

     [ENOTCAPABLE]	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.

BSD
								  March 27, 2014							       BSD