CAP_RIGHTS_LIMIT(2)       FreeBSD 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
     The cap_rights_limit() function first appeared in FreeBSD 8.3.  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.

FreeBSD 13.1-RELEASE-p6           May 5, 2020          FreeBSD 13.1-RELEASE-p6