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    cred::Credential,
12    error::{to_result, Result},
13    fs::File,
14};
15
16/// Calls the security modules to determine if the given task can become the manager of a binder
17/// context.
18#[inline]
19pub fn binder_set_context_mgr(mgr: &Credential) -> Result {
20    // SAFETY: `mrg.0` is valid because the shared reference guarantees a nonzero refcount.
21    to_result(unsafe { bindings::security_binder_set_context_mgr(mgr.as_ptr()) })
22}
23
24/// Calls the security modules to determine if binder transactions are allowed from task `from` to
25/// task `to`.
26#[inline]
27pub fn binder_transaction(from: &Credential, to: &Credential) -> Result {
28    // SAFETY: `from` and `to` are valid because the shared references guarantee nonzero refcounts.
29    to_result(unsafe { bindings::security_binder_transaction(from.as_ptr(), to.as_ptr()) })
30}
31
32/// Calls the security modules to determine if task `from` is allowed to send binder objects
33/// (owned by itself or other processes) to task `to` through a binder transaction.
34#[inline]
35pub fn binder_transfer_binder(from: &Credential, to: &Credential) -> Result {
36    // SAFETY: `from` and `to` are valid because the shared references guarantee nonzero refcounts.
37    to_result(unsafe { bindings::security_binder_transfer_binder(from.as_ptr(), to.as_ptr()) })
38}
39
40/// Calls the security modules to determine if task `from` is allowed to send the given file to
41/// task `to` (which would get its own file descriptor) through a binder transaction.
42#[inline]
43pub fn binder_transfer_file(from: &Credential, to: &Credential, file: &File) -> Result {
44    // SAFETY: `from`, `to` and `file` are valid because the shared references guarantee nonzero
45    // refcounts.
46    to_result(unsafe {
47        bindings::security_binder_transfer_file(from.as_ptr(), to.as_ptr(), file.as_ptr())
48    })
49}
50
51/// A security context string.
52///
53/// # Invariants
54///
55/// The `ctx` field corresponds to a valid security context as returned by a successful call to
56/// `security_secid_to_secctx`, that has not yet been released by `security_release_secctx`.
57pub struct SecurityCtx {
58    ctx: bindings::lsm_context,
59}
60
61impl SecurityCtx {
62    /// Get the security context given its id.
63    #[inline]
64    pub fn from_secid(secid: u32) -> Result<Self> {
65        let mut ctx: bindings::lsm_context = pin_init::zeroed();
66
67        // SAFETY: Just a C FFI call. The pointer is valid for writes.
68        to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut ctx) })?;
69
70        // INVARIANT: If the above call did not fail, then we have a valid security context.
71        Ok(Self { ctx })
72    }
73
74    /// Returns whether the security context is empty.
75    #[inline]
76    pub fn is_empty(&self) -> bool {
77        self.ctx.len == 0
78    }
79
80    /// Returns the length of this security context.
81    #[inline]
82    pub fn len(&self) -> usize {
83        self.ctx.len as usize
84    }
85
86    /// Returns the bytes for this security context.
87    #[inline]
88    pub fn as_bytes(&self) -> &[u8] {
89        let ptr = self.ctx.context;
90        if ptr.is_null() {
91            debug_assert_eq!(self.len(), 0);
92            // We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.
93            return &[];
94        }
95
96        // SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for
97        // `self.len()` bytes. Furthermore, if the length is zero, then we have ensured that the
98        // pointer is not null.
99        unsafe { core::slice::from_raw_parts(ptr.cast(), self.len()) }
100    }
101}
102
103impl Drop for SecurityCtx {
104    #[inline]
105    fn drop(&mut self) {
106        // SAFETY: By the invariant of `Self`, this releases an lsm context that came from a
107        // successful call to `security_secid_to_secctx` and has not yet been released.
108        unsafe { bindings::security_release_secctx(&mut self.ctx) };
109    }
110}
kernel/security.rs

kernel/
security.rs
