cap_rights_limit — limit capability rights

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

Debian                                             May 5, 2020                               CAP_RIGHTS_LIMIT(2)

       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.

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.

       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");

       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.

       Standard C Library (libc, -lc)

       cap_rights_limit — limit capability rights

       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.

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)

#include<sys/capsicum.h>intcap_rights_limit(intfd, constcap_rights_t*rights);