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94d356c033
Add an abstraction for viewing the string representation of a security context. This is needed by Rust Binder because it has a feature where a process can view the string representation of the security context for incoming transactions. The process can use that to authenticate incoming transactions, and since the feature is provided by the kernel, the process can trust that the security context is legitimate. This abstraction makes the following assumptions about the C side: * When a call to `security_secid_to_secctx` is successful, it returns a pointer and length. The pointer references a byte string and is valid for reading for that many bytes. * The string may be referenced until `security_release_secctx` is called. * If CONFIG_SECURITY is set, then the three methods mentioned in rust/helpers are available without a helper. (That is, they are not a #define or `static inline`.) Reviewed-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Reviewed-by: Trevor Gross <tmgross@umich.edu> Reviewed-by: Gary Guo <gary@garyguo.net> Signed-off-by: Alice Ryhl <aliceryhl@google.com> Link: https://lore.kernel.org/r/20240915-alice-file-v10-5-88484f7a3dcf@google.com Acked-by: Paul Moore <paul@paul-moore.com> Reviewed-by: Kees Cook <kees@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
75 lines
2.3 KiB
Rust
75 lines
2.3 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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// Copyright (C) 2024 Google LLC.
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//! Linux Security Modules (LSM).
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//!
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//! C header: [`include/linux/security.h`](srctree/include/linux/security.h).
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use crate::{
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bindings,
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error::{to_result, Result},
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};
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/// A security context string.
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///
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/// # Invariants
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///
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/// The `secdata` and `seclen` fields correspond to a valid security context as returned by a
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/// successful call to `security_secid_to_secctx`, that has not yet been destroyed by calling
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/// `security_release_secctx`.
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pub struct SecurityCtx {
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secdata: *mut core::ffi::c_char,
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seclen: usize,
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}
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impl SecurityCtx {
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/// Get the security context given its id.
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pub fn from_secid(secid: u32) -> Result<Self> {
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let mut secdata = core::ptr::null_mut();
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let mut seclen = 0u32;
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// SAFETY: Just a C FFI call. The pointers are valid for writes.
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to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut secdata, &mut seclen) })?;
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// INVARIANT: If the above call did not fail, then we have a valid security context.
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Ok(Self {
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secdata,
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seclen: seclen as usize,
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})
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}
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/// Returns whether the security context is empty.
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pub fn is_empty(&self) -> bool {
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self.seclen == 0
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}
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/// Returns the length of this security context.
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pub fn len(&self) -> usize {
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self.seclen
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}
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/// Returns the bytes for this security context.
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pub fn as_bytes(&self) -> &[u8] {
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let ptr = self.secdata;
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if ptr.is_null() {
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debug_assert_eq!(self.seclen, 0);
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// We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.
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return &[];
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}
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// SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for
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// `seclen` bytes. Furthermore, if the length is zero, then we have ensured that the
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// pointer is not null.
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unsafe { core::slice::from_raw_parts(ptr.cast(), self.seclen) }
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}
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}
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impl Drop for SecurityCtx {
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fn drop(&mut self) {
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// SAFETY: By the invariant of `Self`, this frees a pointer that came from a successful
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// call to `security_secid_to_secctx` and has not yet been destroyed by
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// `security_release_secctx`.
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unsafe { bindings::security_release_secctx(self.secdata, self.seclen as u32) };
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}
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}
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