projects/linux·blob v6.13 · refs

74 lines · 2.3 KiB

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 `secdata` and `seclen` fields correspond to a valid security context as returned by a
19/// successful call to `security_secid_to_secctx`, that has not yet been destroyed by calling
20/// `security_release_secctx`.
21pub struct SecurityCtx {
22 secdata: *mut core::ffi::c_char,
23 seclen: usize,
24}
25
26impl SecurityCtx {
27 /// Get the security context given its id.
28 pub fn from_secid(secid: u32) -> Result<Self> {
29 let mut secdata = core::ptr::null_mut();
30 let mut seclen = 0u32;
31 // SAFETY: Just a C FFI call. The pointers are valid for writes.
32 to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut secdata, &mut seclen) })?;
33
34 // INVARIANT: If the above call did not fail, then we have a valid security context.
35 Ok(Self {
36 secdata,
37 seclen: seclen as usize,
38 })
39 }
40
41 /// Returns whether the security context is empty.
42 pub fn is_empty(&self) -> bool {
43 self.seclen == 0
44 }
45
46 /// Returns the length of this security context.
47 pub fn len(&self) -> usize {
48 self.seclen
49 }
50
51 /// Returns the bytes for this security context.
52 pub fn as_bytes(&self) -> &[u8] {
53 let ptr = self.secdata;
54 if ptr.is_null() {
55 debug_assert_eq!(self.seclen, 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 // `seclen` 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.seclen) }
64 }
65}
66
67impl Drop for SecurityCtx {
68 fn drop(&mut self) {
69 // SAFETY: By the invariant of `Self`, this frees a pointer that came from a successful
70 // call to `security_secid_to_secctx` and has not yet been destroyed by
71 // `security_release_secctx`.
72 unsafe { bindings::security_release_secctx(self.secdata, self.seclen as u32) };
73 }
74}