// 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 `secdata` and `seclen` fields correspond to a valid security context as returned by a/// successful call to `security_secid_to_secctx`, that has not yet been destroyed by calling/// `security_release_secctx`.pub struct SecurityCtx {    secdata: *mut core::ffi::c_char,    seclen: usize,} impl SecurityCtx {    /// Get the security context given its id.    pub fn from_secid(secid: u32) -> Result<Self> {        let mut secdata = core::ptr::null_mut();        let mut seclen = 0u32;        // SAFETY: Just a C FFI call. The pointers are valid for writes.        to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut secdata, &mut seclen) })?;         // INVARIANT: If the above call did not fail, then we have a valid security context.        Ok(Self {            secdata,            seclen: seclen as usize,        })    }     /// Returns whether the security context is empty.    pub fn is_empty(&self) -> bool {        self.seclen == 0    }     /// Returns the length of this security context.    pub fn len(&self) -> usize {        self.seclen    }     /// Returns the bytes for this security context.    pub fn as_bytes(&self) -> &[u8] {        let ptr = self.secdata;        if ptr.is_null() {            debug_assert_eq!(self.seclen, 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        // `seclen` 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.seclen) }    }} impl Drop for SecurityCtx {    fn drop(&mut self) {        // SAFETY: By the invariant of `Self`, this frees a pointer that came from a successful        // call to `security_secid_to_secctx` and has not yet been destroyed by        // `security_release_secctx`.        unsafe { bindings::security_release_secctx(self.secdata, self.seclen as u32) };    }}