cap_getmode(2) [freebsd man page]

CAP_ENTER(2)						      BSD System Calls Manual						      CAP_ENTER(2)

NAME

     cap_enter, cap_getmode -- Capability mode system calls

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/capsicum.h>

     int
     cap_enter(void);

     int
     cap_getmode(u_int *modep);

DESCRIPTION

     cap_enter() places the current process into capability mode, a mode of execution in which processes may only issue system calls operating on
     file descriptors or reading limited global system state.  Access to global name spaces, such as file system or IPC name spaces, is prevented.
     If the process is already in a capability mode sandbox, the system call is a no-op.  Future process descendants created with fork(2) or
     pdfork(2) will be placed in capability mode from inception.

     When combined with cap_rights_limit(2), cap_ioctls_limit(2), cap_fcntls_limit(2), cap_enter() may be used to create kernel-enforced sandboxes
     in which appropriately-crafted applications or application components may be run.

     cap_getmode() returns a flag indicating whether or not the process is in a capability mode sandbox.

CAVEAT

     Creating effective process sandboxes is a tricky process that involves identifying the least possible rights required by the process and then
     passing those rights into the process in a safe manner.  Consumers of cap_enter() should also be aware of other inherited rights, such as
     access to VM resources, memory contents, and other process properties that should be considered.  It is advisable to use fexecve(2) to create
     a runtime environment inside the sandbox that has as few implicitly acquired rights as possible.

RETURN VALUES

     The cap_enter() and cap_getmode() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

ERRORS

     The cap_enter() and cap_getmode() system calls will fail if:

     [ENOSYS]		The kernel is compiled without:

			options CAPABILITY_MODE

     The cap_getmode() system call may also return the following error:

     [EFAULT]		Pointer modep points outside the process's allocated address space.

SEE ALSO

     cap_fcntls_limit(2), cap_ioctls_limit(2), cap_rights_limit(2), fexecve(2), cap_sandboxed(3), capsicum(4)

HISTORY

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

AUTHORS

     These functions and the capability facility were created by Robert N. M. Watson at the University of Cambridge Computer Laboratory with sup-
     port from a grant from Google, Inc.

BSD
								  March 27, 2014							       BSD

Check Out this Related Man Page

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

Linux and UNIX Man Pages

cap_getmode(2) [freebsd man page]

Check Out this Related Man Page