// SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2024 Google LLC. //! Linux Security Modules (LSM).//!//! C header: [`include/linux/security.h`](srctree/include/linux/security.h). use crate::{    bindings,    error::{to_result, Result},}; /// A security context string.////// # Invariants////// The `ctx` field corresponds to a valid security context as returned by a successful call to/// `security_secid_to_secctx`, that has not yet been released by `security_release_secctx`.pub struct SecurityCtx {    ctx: bindings::lsm_context,} impl SecurityCtx {    /// Get the security context given its id.    #[inline]    pub fn from_secid(secid: u32) -> Result<Self> {        // SAFETY: `struct lsm_context` can be initialized to all zeros.        let mut ctx: bindings::lsm_context = unsafe { core::mem::zeroed() };         // SAFETY: Just a C FFI call. The pointer is valid for writes.        to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut ctx) })?;         // INVARIANT: If the above call did not fail, then we have a valid security context.        Ok(Self { ctx })    }     /// Returns whether the security context is empty.    #[inline]    pub fn is_empty(&self) -> bool {        self.ctx.len == 0    }     /// Returns the length of this security context.    #[inline]    pub fn len(&self) -> usize {        self.ctx.len as usize    }     /// Returns the bytes for this security context.    #[inline]    pub fn as_bytes(&self) -> &[u8] {        let ptr = self.ctx.context;        if ptr.is_null() {            debug_assert_eq!(self.len(), 0);            // We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.            return &[];        }         // SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for        // `self.len()` bytes. Furthermore, if the length is zero, then we have ensured that the        // pointer is not null.        unsafe { core::slice::from_raw_parts(ptr.cast(), self.len()) }    }} impl Drop for SecurityCtx {    #[inline]    fn drop(&mut self) {        // SAFETY: By the invariant of `Self`, this releases an lsm context that came from a        // successful call to `security_secid_to_secctx` and has not yet been released.        unsafe { bindings::security_release_secctx(&mut self.ctx) };    }}