From: Alice Ryhl <aliceryhl@google.com>
To: "Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <benno.lossin@proton.me>,
"Andreas Hindborg" <a.hindborg@samsung.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Christian Brauner" <brauner@kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Martijn Coenen" <maco@android.com>,
"Joel Fernandes" <joel@joelfernandes.org>,
"Carlos Llamas" <cmllamas@google.com>,
"Suren Baghdasaryan" <surenb@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Kees Cook <keescook@chromium.org>,
Matthew Wilcox <willy@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>, Daniel Xu <dxu@dxuuu.xyz>,
linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
linux-fsdevel@vger.kernel.org, Alice Ryhl <aliceryhl@google.com>,
Trevor Gross <tmgross@umich.edu>,
Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Subject: [PATCH v6 4/8] rust: cred: add Rust abstraction for `struct cred`
Date: Fri, 17 May 2024 09:30:37 +0000 [thread overview]
Message-ID: <20240517-alice-file-v6-4-b25bafdc9b97@google.com> (raw)
In-Reply-To: <20240517-alice-file-v6-0-b25bafdc9b97@google.com>
From: Wedson Almeida Filho <wedsonaf@gmail.com>
Add a wrapper around `struct cred` called `Credential`, and provide
functionality to get the `Credential` associated with a `File`.
Rust Binder must check the credentials of processes when they attempt to
perform various operations, and these checks usually take a
`&Credential` as parameter. The security_binder_set_context_mgr function
would be one example. This patch is necessary to access these security_*
methods from Rust.
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Co-developed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 13 ++++++++
rust/kernel/cred.rs | 74 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/file.rs | 13 ++++++++
rust/kernel/lib.rs | 1 +
5 files changed, 102 insertions(+)
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 541afef7ddc4..94091cb337e9 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
*/
#include <kunit/test.h>
+#include <linux/cred.h>
#include <linux/errname.h>
#include <linux/ethtool.h>
#include <linux/file.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 5545a00560d1..56415bce8af0 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -23,6 +23,7 @@
#include <kunit/test-bug.h>
#include <linux/bug.h>
#include <linux/build_bug.h>
+#include <linux/cred.h>
#include <linux/err.h>
#include <linux/errname.h>
#include <linux/fs.h>
@@ -164,6 +165,18 @@ struct file *rust_helper_get_file(struct file *f)
}
EXPORT_SYMBOL_GPL(rust_helper_get_file);
+const struct cred *rust_helper_get_cred(const struct cred *cred)
+{
+ return get_cred(cred);
+}
+EXPORT_SYMBOL_GPL(rust_helper_get_cred);
+
+void rust_helper_put_cred(const struct cred *cred)
+{
+ put_cred(cred);
+}
+EXPORT_SYMBOL_GPL(rust_helper_put_cred);
+
/*
* `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
* use it in contexts where Rust expects a `usize` like slice (array) indices.
diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs
new file mode 100644
index 000000000000..360d6fdbe5e7
--- /dev/null
+++ b/rust/kernel/cred.rs
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Credentials management.
+//!
+//! C header: [`include/linux/cred.h`](srctree/include/linux/cred.h).
+//!
+//! Reference: <https://www.kernel.org/doc/html/latest/security/credentials.html>
+
+use crate::{
+ bindings,
+ types::{AlwaysRefCounted, Opaque},
+};
+
+/// Wraps the kernel's `struct cred`.
+///
+/// Credentials are used for various security checks in the kernel.
+///
+/// Most fields of credentials are immutable. When things have their credentials changed, that
+/// happens by replacing the credential instead of changing an existing credential. See the [kernel
+/// documentation][ref] for more info on this.
+///
+/// # Invariants
+///
+/// Instances of this type are always ref-counted, that is, a call to `get_cred` ensures that the
+/// allocation remains valid at least until the matching call to `put_cred`.
+///
+/// [ref]: https://www.kernel.org/doc/html/latest/security/credentials.html
+#[repr(transparent)]
+pub struct Credential(Opaque<bindings::cred>);
+
+// SAFETY:
+// - `Credential::dec_ref` can be called from any thread.
+// - It is okay to send ownership of `Credential` across thread boundaries.
+unsafe impl Send for Credential {}
+
+// SAFETY: It's OK to access `Credential` through shared references from other threads because
+// we're either accessing properties that don't change or that are properly synchronised by C code.
+unsafe impl Sync for Credential {}
+
+impl Credential {
+ /// Creates a reference to a [`Credential`] from a valid pointer.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the
+ /// returned [`Credential`] reference.
+ pub unsafe fn from_ptr<'a>(ptr: *const bindings::cred) -> &'a Credential {
+ // SAFETY: The safety requirements guarantee the validity of the dereference, while the
+ // `Credential` type being transparent makes the cast ok.
+ unsafe { &*ptr.cast() }
+ }
+
+ /// Returns the effective UID of the given credential.
+ pub fn euid(&self) -> bindings::kuid_t {
+ // SAFETY: By the type invariant, we know that `self.0` is valid. Furthermore, the `euid`
+ // field of a credential is never changed after initialization, so there is no potential
+ // for data races.
+ unsafe { (*self.0.get()).euid }
+ }
+}
+
+// SAFETY: The type invariants guarantee that `Credential` is always ref-counted.
+unsafe impl AlwaysRefCounted for Credential {
+ fn inc_ref(&self) {
+ // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+ unsafe { bindings::get_cred(self.0.get()) };
+ }
+
+ unsafe fn dec_ref(obj: core::ptr::NonNull<Credential>) {
+ // SAFETY: The safety requirements guarantee that the refcount is nonzero. The cast is okay
+ // because `Credential` has the same representation as `struct cred`.
+ unsafe { bindings::put_cred(obj.cast().as_ptr()) };
+ }
+}
diff --git a/rust/kernel/file.rs b/rust/kernel/file.rs
index ad881e67084c..755816eb38ef 100644
--- a/rust/kernel/file.rs
+++ b/rust/kernel/file.rs
@@ -7,6 +7,7 @@
use crate::{
bindings,
+ cred::Credential,
error::{code::*, Error, Result},
types::{ARef, AlwaysRefCounted, Opaque},
};
@@ -283,6 +284,18 @@ pub fn as_ptr(&self) -> *mut bindings::file {
self.inner.get()
}
+ /// Returns the credentials of the task that originally opened the file.
+ pub fn cred(&self) -> &Credential {
+ // SAFETY: It's okay to read the `f_cred` field without synchronization because `f_cred` is
+ // never changed after initialization of the file.
+ let ptr = unsafe { (*self.as_ptr()).f_cred };
+
+ // SAFETY: The signature of this function ensures that the caller will only access the
+ // returned credential while the file is still valid, and the C side ensures that the
+ // credential stays valid at least as long as the file.
+ unsafe { Credential::from_ptr(ptr) }
+ }
+
/// Returns the flags associated with the file.
///
/// The flags are a combination of the constants in [`flags`].
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index c583fd27736d..cc629a74137f 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -28,6 +28,7 @@
pub mod alloc;
mod build_assert;
+pub mod cred;
pub mod error;
pub mod file;
pub mod init;
--
2.45.0.rc1.225.g2a3ae87e7f-goog
next prev parent reply other threads:[~2024-05-17 9:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-17 9:30 [PATCH v6 0/8] File abstractions needed by Rust Binder Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 1/8] rust: types: add `NotThreadSafe` Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 2/8] rust: task: add `Task::current_raw` Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 3/8] rust: file: add Rust abstraction for `struct file` Alice Ryhl
2024-05-24 16:12 ` Christian Brauner
2024-05-24 19:17 ` Alice Ryhl
2024-05-24 21:32 ` Al Viro
2024-05-27 16:03 ` Alice Ryhl
2024-05-28 19:36 ` Al Viro
2024-05-28 20:29 ` Alice Ryhl
2024-05-28 20:59 ` Al Viro
2024-05-24 22:56 ` Al Viro
2024-05-25 0:33 ` Al Viro
2024-05-25 15:40 ` Al Viro
2024-05-25 11:53 ` Christian Brauner
2024-05-27 16:05 ` Alice Ryhl
2024-05-29 8:17 ` Christian Brauner
2024-05-29 12:58 ` Alice Ryhl
2024-05-17 9:30 ` Alice Ryhl [this message]
2024-05-17 9:30 ` [PATCH v6 5/8] rust: security: add abstraction for secctx Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 6/8] rust: file: add `FileDescriptorReservation` Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 7/8] rust: file: add `Kuid` wrapper Alice Ryhl
2024-05-17 9:30 ` [PATCH v6 8/8] rust: file: add abstraction for `poll_table` Alice Ryhl
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240517-alice-file-v6-4-b25bafdc9b97@google.com \
--to=aliceryhl@google.com \
--cc=a.hindborg@samsung.com \
--cc=alex.gaynor@gmail.com \
--cc=arve@android.com \
--cc=benno.lossin@proton.me \
--cc=bjorn3_gh@protonmail.com \
--cc=boqun.feng@gmail.com \
--cc=brauner@kernel.org \
--cc=cmllamas@google.com \
--cc=dan.j.williams@intel.com \
--cc=dxu@dxuuu.xyz \
--cc=gary@garyguo.net \
--cc=gregkh@linuxfoundation.org \
--cc=joel@joelfernandes.org \
--cc=keescook@chromium.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maco@android.com \
--cc=ojeda@kernel.org \
--cc=peterz@infradead.org \
--cc=rust-for-linux@vger.kernel.org \
--cc=surenb@google.com \
--cc=tglx@linutronix.de \
--cc=tkjos@android.com \
--cc=tmgross@umich.edu \
--cc=viro@zeniv.linux.org.uk \
--cc=wedsonaf@gmail.com \
--cc=willy@infradead.org \
--cc=yakoyoku@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).