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// 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) };
}
}
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