Capsicum is an implementation of

capability-based security Capability-based security is a concept in the design of secure computing systems, one of the existing security models. A capability (known in some systems as a key) is a communicable, unforgeable token of authority. It refers to a value that refe ...

for

UNIX Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

and similar systems. Presented at USENIX 2010, the system is part of

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

since its 9.0 release. It has also been adapted to

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

and

DragonflyBSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in Jun ...

in the form of kernel patches. The system works by chunking the normal permissions up into very small pieces. When a process enters capsicum mode, it loses all permissions normally associated with its controlling user, with the exception of "capabilities" it already has in the form of

file descriptor In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have ...

s. A process can also receive capabilities via

Unix socket Unix (; trademarked as UNIX) is a family of Computer multitasking, multitasking, multiuser computer operating systems that derive from the original AT&T Corporation, AT&T Unix, whose development started in 1969 at the Bell Labs research center ...

s. These file descriptors not only control access to the

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

, but also to other devices like the network sockets.

Flags A flag is a piece of textile, fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term ''flag'' is also used to refer to the graphic desi ...

are also used to control more fine-grained access like reads and writes.

CloudABI

CloudABI is an

application binary interface In computer software, an application binary interface (ABI) is an interface between two binary program modules. Often, one of these modules is a library or operating system facility, and the other is a program that is being run by a user. An ' ...

based on capsicum. It keeps the overall capsicum permission model, but uses it to redesign a simplified environment for processes (system calls, C library, etc.) to run on, so that programs become portable to any platform supporting the ABI on the same

instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ' ...

. The interface it offers is roughly

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...

minus parts that do not work with capability-based security. , CloudABI is natively a part of

, and it can be run on other systems either via a Capsicum-based patch or using a non-secure

system call In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, acc ...

emulator. As of October 2020, CloudABI has been deprecated in favor of WebAssembly System Interface for lack of interest.

References

External links

* * {{Object-capability security Computer security models Access control Capability systems