NAME

     cap_enter, cap_getmode — Capability mode system calls

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/capability.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 create with fork(2) or pdfork(2) will be placed in
     capability mode from inception.

     When combined with capabilities created with cap_new(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.  See the CAVEAT section of cap_new(2) for why this is particularly tricky with
     UNIX file descriptors as the canonical representation of a right.  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.

SEE ALSO

     cap_new(2), fexecve(2), 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.