1// SPDX-License-Identifier: GPL-2.0
2
3// Copyright (C) 2024 Google LLC.
4
5//! Linux Security Modules (LSM).
6//!
7//! C header: [`include/linux/security.h`](srctree/include/linux/security.h).
8
9use crate::{
10 bindings,
11 error::{to_result, Result},
12};
13
14/// A security context string.
15///
16/// # Invariants
17///
18/// The `ctx` field corresponds to a valid security context as returned by a successful call to
19/// `security_secid_to_secctx`, that has not yet been released by `security_release_secctx`.
20pub struct SecurityCtx {
21 ctx: bindings::lsm_context,
22}
23
24impl SecurityCtx {
25 /// Get the security context given its id.
26 #[inline]
27 pub fn from_secid(secid: u32) -> Result<Self> {
28 // SAFETY: `struct lsm_context` can be initialized to all zeros.
29 let mut ctx: bindings::lsm_context = unsafe { core::mem::zeroed() };
30
31 // SAFETY: Just a C FFI call. The pointer is valid for writes.
32 to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut ctx) })?;
33
34 // INVARIANT: If the above call did not fail, then we have a valid security context.
35 Ok(Self { ctx })
36 }
37
38 /// Returns whether the security context is empty.
39 #[inline]
40 pub fn is_empty(&self) -> bool {
41 self.ctx.len == 0
42 }
43
44 /// Returns the length of this security context.
45 #[inline]
46 pub fn len(&self) -> usize {
47 self.ctx.len as usize
48 }
49
50 /// Returns the bytes for this security context.
51 #[inline]
52 pub fn as_bytes(&self) -> &[u8] {
53 let ptr = self.ctx.context;
54 if ptr.is_null() {
55 debug_assert_eq!(self.len(), 0);
56 // We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.
57 return &[];
58 }
59
60 // SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for
61 // `self.len()` bytes. Furthermore, if the length is zero, then we have ensured that the
62 // pointer is not null.
63 unsafe { core::slice::from_raw_parts(ptr.cast(), self.len()) }
64 }
65}
66
67impl Drop for SecurityCtx {
68 #[inline]
69 fn drop(&mut self) {
70 // SAFETY: By the invariant of `Self`, this releases an lsm context that came from a
71 // successful call to `security_secid_to_secctx` and has not yet been released.
72 unsafe { bindings::security_release_secctx(&mut self.ctx) };
73 }
74}
75

source code of linux/rust/kernel/security.rs