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CAP_ENTER(2) FreeBSD 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.
RUN-TIME SETTINGS
If the kern.trap_enotcap sysctl MIB is set to a non-zero value, then for
any process executing in a capability mode sandbox, any syscall which
results in either an ENOTCAPABLE or ECAPMODE error also generates the
synchronous SIGTRAP signal to the thread on the syscall return. On
signal delivery, the si_errno member of the siginfo signal handler
parameter is set to the syscall error value, and the si_code member is
set to TRAP_CAP.
See also the PROC_TRAPCAP_CTL and PROC_TRAPCAP_STATUS operations of the
procctl(2) function for similar per-process functionality.
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.
When the process is in capability mode, cap_getmode() sets the flag to a
non-zero value. A zero value means the process is not in capability
mode.
ERRORS
The cap_enter() and cap_getmode() system calls will fail if:
[ENOSYS] The running kernel was compiled without options
SEE ALSO
cap_fcntls_limit(2), cap_ioctls_limit(2), cap_rights_limit(2),
fexecve(2), procctl(2), cap_sandboxed(3), capsicum(4), sysctl(9)
HISTORY
The cap_getmode() system call first appeared in FreeBSD 8.3. 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 support
from a grant from Google, Inc.
CAVEATS
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.
FreeBSD 14.0-RELEASE-p6 March 9, 2023 FreeBSD 14.0-RELEASE-p6