kernel/
security.rs

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}
kernel/security.rs

kernel/
security.rs
