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        // SAFETY: `struct lsm_context` can be initialized to all zeros.
 66        let mut ctx: bindings::lsm_context = unsafe { core::mem::zeroed() };
 67
 68        // SAFETY: Just a C FFI call. The pointer is valid for writes.
 69        to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut ctx) })?;
 70
 71        // INVARIANT: If the above call did not fail, then we have a valid security context.
 72        Ok(Self { ctx })
 73    }
 74
 75    /// Returns whether the security context is empty.
 76    #[inline]
 77    pub fn is_empty(&self) -> bool {
 78        self.ctx.len == 0
 79    }
 80
 81    /// Returns the length of this security context.
 82    #[inline]
 83    pub fn len(&self) -> usize {
 84        self.ctx.len as usize
 85    }
 86
 87    /// Returns the bytes for this security context.
 88    #[inline]
 89    pub fn as_bytes(&self) -> &[u8] {
 90        let ptr = self.ctx.context;
 91        if ptr.is_null() {
 92            debug_assert_eq!(self.len(), 0);
 93            // We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.
 94            return &[];
 95        }
 96
 97        // SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for
 98        // `self.len()` bytes. Furthermore, if the length is zero, then we have ensured that the
 99        // pointer is not null.
100        unsafe { core::slice::from_raw_parts(ptr.cast(), self.len()) }
101    }
102}
103
104impl Drop for SecurityCtx {
105    #[inline]
106    fn drop(&mut self) {
107        // SAFETY: By the invariant of `Self`, this releases an lsm context that came from a
108        // successful call to `security_secid_to_secctx` and has not yet been released.
109        unsafe { bindings::security_release_secctx(&mut self.ctx) };
110    }
111}