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 ref ...

for

UNIX Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user 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, a ...

and similar systems. Presented at

USENIX USENIX is an American 501(c)(3) nonprofit membership organization based in Berkeley, California and founded in 1975 that supports advanced computing systems, operating system (OS), and computer networking research. It organizes several confe ...

2010, the system is part of

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

since its 9.0 release. It has also been adapted to DragonflyBSD in the form of kernel patches. Further technical details can be found in the Ph.D. thesis by Robert Watson. 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, except "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 h ...

s. A process can also receive capabilities via Unix sockets. These file descriptors not only control access to the file system, but also to other devices like the network sockets.

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

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

CloudABI

CloudABI is an

application binary interface An application binary interface (ABI) is an interface exposed by software that is defined for in-process machine code access. Often, the exposing software is a library, and the consumer is a program. An ABI is at a relatively low-level of a ...

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) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, ...

. 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 application programming interfaces (APIs), along with comm ...

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 (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, accessing a hard disk drive ...

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