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.
[ENOSYS] The running kernel was compiled without options
CAPABILITY_MODE.
[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 <
[email protected]>
under sponsorship of the FreeBSD Foundation.
FreeBSD 14.1-RELEASE-p8 March 9, 2023 FreeBSD 14.1-RELEASE-p8