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CAPSICUM(4)	       FreeBSD Kernel Interfaces Manual		   CAPSICUM(4)

     Capsicum -- lightweight OS	capability and sandbox framework

     options CAPABILITY_MODE
     options CAPABILITIES

     Capsicum is a lightweight OS capability and sandbox framework implement-
     ing a hybrid capability system model.  Capabilities are unforgeable to-
     kens of authority that can	be delegated and must be presented to perform
     an	action.	 Capsicum makes	file descriptors into capabilities.

     Capsicum can be used for application and library compartmentalisation,
     the decomposition of larger bodies	of software into isolated (sandboxed)
     components	in order to implement security policies	and limit the impact
     of	software vulnerabilities.

     Capsicum provides two core	kernel primitives:

     capability	mode
	     A process mode, entered by	invoking cap_enter(2), in which	access
	     to	global OS namespaces (such as the file system and PID name-
	     spaces) is	restricted; only explicitly delegated rights, refer-
	     enced by memory mappings or file descriptors, may be used.	 Once
	     set, the flag is inherited	by future children processes, and may
	     not be cleared.

	     Limit operations that can be called on file descriptors.  For ex-
	     ample, a file descriptor returned by open(2) may be refined using
	     cap_rights_limit(2) so that only read(2) and write(2) can be
	     called, but not fchmod(2).	 The complete list of the capability
	     rights can	be found in the	rights(4) manual page.

     In	some cases, Capsicum requires use of alternatives to traditional POSIX
     APIs in order to name objects using capabilities rather than global name-

     process descriptors
	     File descriptors representing processes, allowing parent pro-
	     cesses to manage child processes without requiring	access to the
	     PID namespace; described in greater detail	in procdesc(4).

     anonymous shared memory
	     An	extension to the POSIX shared memory API to support anonymous
	     swap objects associated with file descriptors; described in
	     greater detail in shm_open(2).

     In	some cases, Capsicum limits the	valid values of	some parameters	to
     traditional APIs in order to restrict access to global namespaces:

     process IDs
	     Processes can only	act upon their own process ID with syscalls
	     such as cpuset_setaffinity(2).

     cap_enter(2), cap_fcntls_limit(2),	cap_getmode(2),	cap_ioctls_limit(2),
     cap_rights_limit(2), fchmod(2), open(2), pdfork(2), pdgetpid(2),
     pdkill(2),	pdwait4(2), read(2), shm_open(2), write(2), cap_rights_get(3),
     libcasper(3), procdesc(4)

     Capsicum first appeared in	FreeBSD	9.0, and was developed at the Univer-
     sity of Cambridge.

     Capsicum was developed by Robert Watson <> and
     Jonathan Anderson <> at the University	of Cambridge,
     and Ben Laurie <> and Kris	Kennaway <> at
     Google, Inc., and Pawel Jakub Dawidek <>.

FreeBSD	13.0			April 19, 2022			  FreeBSD 13.0


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