xref: /freebsd/share/man/man4/capsicum.4 (revision c3786ca8bc5ba471edae059393bb7bac6400ac2a)

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.Dd January 3, 2024
.Dt CAPSICUM 4
.Os
.Sh NAME
.Nm Capsicum
.Nd lightweight OS capability and sandbox framework
.Sh SYNOPSIS
.Cd "options CAPABILITY_MODE"
.Cd "options CAPABILITIES"
.Sh DESCRIPTION
.Nm
is a lightweight OS capability and sandbox framework implementing a hybrid
capability system model.
Capabilities are unforgeable tokens of authority that can be delegated and must
be presented to perform an action.
.Nm
makes file descriptors into capabilities.
.Pp
.Nm
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.
.Pp
.Nm
provides two core kernel primitives:
.Bl -tag -width indent
.It capability mode
A process mode, entered by invoking
.Xr cap_enter 2 ,
in which access to global OS namespaces (such as the file system and PID
namespaces) is restricted; only explicitly delegated rights, referenced by
memory mappings or file descriptors, may be used.
Once set, the flag is inherited by future children processes, and may not be
cleared.
.It capabilities
Limit operations that can be called on file descriptors.
For example, a file descriptor returned by
.Xr open 2
may be refined using
.Xr cap_rights_limit 2
so that only
.Xr read 2
and
.Xr write 2
can be called, but not
.Xr fchmod 2 .
The complete list of the capability rights can be found in the
.Xr rights 4
manual page.
.El
.Pp
In some cases,
.Nm
requires use of alternatives to traditional POSIX APIs in order to name
objects using capabilities rather than global namespaces:
.Bl -tag -width indent
.It process descriptors
File descriptors representing processes, allowing parent processes to manage
child processes without requiring access to the PID namespace; described in
greater detail in
.Xr procdesc 4 .
.It 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
.Xr shm_open 2 .
.El
.Pp
In some cases,
.Nm
limits the valid values of some parameters to traditional APIs in order to
restrict access to global namespaces:
.Bl -tag -width indent
.It process IDs
Processes can only act upon their own process ID with syscalls such as
.Xr cpuset_setaffinity 2 .
.El
.Sh SEE ALSO
.Xr cap_enter 2 ,
.Xr cap_fcntls_limit 2 ,
.Xr cap_getmode 2 ,
.Xr cap_ioctls_limit 2 ,
.Xr cap_rights_limit 2 ,
.Xr fchmod 2 ,
.Xr open 2 ,
.Xr pdfork 2 ,
.Xr pdgetpid 2 ,
.Xr pdkill 2 ,
.Xr pdwait4 2 ,
.Xr read 2 ,
.Xr shm_open 2 ,
.Xr write 2 ,
.Xr cap_rights_get 3 ,
.Xr capsicum_helpers 3 ,
.Xr libcasper 3 ,
.Xr procdesc 4
.Sh HISTORY
.Nm
first appeared in
.Fx 9.0 ,
and was developed at the University of Cambridge.
.Sh AUTHORS
.Nm
was developed by
.An -nosplit
.An Robert Watson Aq Mt rwatson@FreeBSD.org
and
.An Jonathan Anderson Aq Mt jonathan@FreeBSD.org
at the University of Cambridge, and
.An Ben Laurie Aq Mt benl@FreeBSD.org
and
.An Kris Kennaway Aq Mt kris@FreeBSD.org
at Google, Inc., and
.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net .