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ladybird/Base/usr/share/man/man2/pledge.md
Andreas Kling 95504b5850 Base: Note in pledge(2) man page which promises are extensions 
Also add a little "History" section noting that pledge() is an original
OpenBSD invention and that our implementation differs in many ways.
2020-01-23 10:41:07 +01:00

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Name

pledge - reduce process capabilities

Synopsis

#include <unistd.h>

int pledge(const char* promises, const char* execpromises);

Description

pledge() makes a promise to the kernel that from this moment on, the calling process will only use a subset of system functionality.

Functionality is divided into a curated set of promises (described below), which can be combined to cover the program's needs. Both arguments are space-separated lists of promises.

Note that pledge() can be called repeatedly to remove previously-pledged promises, but it can never regain capabilities once lost.

promises are applied to the current process, and will also be inherited by children created by fork(2).

execpromises are applied if/when a new process image is created with exec(2).

If promises or execpromises is null, the corresponding value is unchanged.

Promises

  • stdio: Basic I/O, memory allocation, information about self, various non-destructive syscalls
  • thread: The POSIX threading API (*)
  • id: Ability to change UID/GID
  • tty: TTY related functionality
  • proc: Process and scheduling related functionality
  • exec: The exec(2) syscall
  • unix: UNIX local domain sockets
  • inet: IPv4 domain sockets
  • accept: May use accept(2) to accept incoming socket connections on already listening sockets. It also allows getsockopt(2) with SOL_SOCKET and SO_PEERCRED on local sockets (*)
  • rpath: "Read" filesystem access
  • wpath: "Write" filesystem access
  • cpath: "Create" filesystem access
  • dpath: Creating new device files
  • chown: Changing file owner/group
  • fattr: Changing file attributes/permissions
  • shared_buffer: Shared memory buffers (*)
  • chroot: The chroot(2) syscall (*)
  • video: May use ioctl(2) and mmap(2) on framebuffer video devices

Promises marked with an asterisk (*) are SerenityOS specific extensions not supported by the original OpenBSD pledge().

Errors

  • EFAULT: promises and/or execpromises are not null and not in readable memory.
  • EINVAL: One or more invalid promises were specified.
  • EPERM: An attempt to increase capabilities was rejected.

History

The pledge() system call was first introduced by OpenBSD. The implementation in SerenityOS differs in many ways and is by no means final.