cap_enter (2)

Leading comments

Copyright (c) 2008-2009 Robert N. M. Watson
All rights reserved.

This software was developed at the University of Cambridge Computer
Laboratory with support from a grant from Google, Inc.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form...

(The comments found at the beginning of the groff file "man2/cap_enter.2freebsd".)

NAME

cap_enter cap_getmode - Capability mode system calls

LIBRARY

Lb libc

SYNOPSIS

In sys/capability.h Ft int Fn cap_enter void Ft int Fn cap_getmode u_int *modep

DESCRIPTION

Fn 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_limit2, cap_ioctls_limit2, cap_fcntls_limit2, Fn cap_enter may be used to create kernel-enforced sandboxes in which appropriately-crafted applications or application components may be run.

Fn 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 Fn 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

Rv -std cap_enter cap_getmode

ERRORS

The Fn cap_enter and Fn cap_getmode system calls will fail if:

Bq Er ENOSYS

The kernel is compiled without:

options CAPABILITY_MODE

The Fn cap_getmode system call may also return the following error:

Bq Er EFAULT

Pointer Fa modep points outside the process's allocated address space.

SEE ALSO

cap_fcntls_limit2, cap_ioctls_limit2, cap_rights_limit2, fexecve(2), cap_sandboxed3, 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 An Robert N. M. Watson at the University of Cambridge Computer Laboratory with support from a grant from Google, Inc.