table of contents
CAP_ENTER(2) | 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 ofcap_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¶
Thecap_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¶
Thecap_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 support from a grant from Google, Inc.March 27, 2014 | Linux 4.9.0-9-amd64 |