starry-kernel 0.10.0

A Linux-compatible OS kernel built on ArceOS unikernel
Documentation 
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//! Linux IPC permission records shared by in-kernel IPC objects.

use bytemuck::AnyBitPattern;
use linux_raw_sys::{
    ctypes::{c_long, c_ushort},
    general::*,
};

// Permission bits
const USER_READ: u32 = 0o400;
const USER_WRITE: u32 = 0o200;
const GROUP_READ: u32 = 0o040;
const GROUP_WRITE: u32 = 0o020;
const OTHER_READ: u32 = 0o004;
const OTHER_WRITE: u32 = 0o002;

/// Data structure used to pass permission information to IPC operations.
#[repr(C)]
#[derive(Clone, Copy, AnyBitPattern, bytemuck::NoUninit)]
pub struct IpcPerm {
    /// Key supplied to msgget(2)
    pub key: __kernel_key_t,
    /// Effective UID of owner
    pub uid: __kernel_uid_t,
    /// Effective GID of owner
    pub gid: __kernel_gid_t,
    /// Effective UID of creator
    pub cuid: __kernel_uid_t,
    /// Effective GID of creator
    pub cgid: __kernel_gid_t,
    /// Permissions (least significant 9 bits define access permissions)
    pub mode: __kernel_mode_t,
    /// Sequence number
    pub seq: c_ushort,
    /// Padding
    pub pad: c_ushort,
    /// Explicitly initialized ABI alignment bytes before the 64-bit fields.
    pub alignment_pad: u32,
    /// Unused field
    pub unused0: c_long,
    /// Unused field
    pub unused1: c_long,
}

impl IpcPerm {
    /// Applies the fields that Linux permits userspace to change via IPC_SET.
    pub(crate) fn update_from_user(&mut self, requested: &Self) {
        const PERMISSION_BITS: __kernel_mode_t = 0o777;

        self.uid = requested.uid;
        self.gid = requested.gid;
        self.mode = (self.mode & !PERMISSION_BITS) | (requested.mode & PERMISSION_BITS);
    }
}

// add a helper function to check IPC permissions
pub(crate) fn has_ipc_permission(
    perm: &IpcPerm,
    current_uid: u32,
    current_gid: u32,
    is_write: bool,
) -> bool {
    // root user has all permissions
    if current_uid == 0 {
        return true;
    }

    if perm.uid == current_uid {
        (perm.mode & if is_write { USER_WRITE } else { USER_READ }) != 0
    } else if perm.gid == current_gid {
        (perm.mode & if is_write { GROUP_WRITE } else { GROUP_READ }) != 0
    } else {
        (perm.mode & if is_write { OTHER_WRITE } else { OTHER_READ }) != 0
    }
}