linux-kernel - Re: [PATCH v4 4/9] rust: cred: add Rust abstraction for `struct cred`

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Message-ID: <aa0f46bc-6bed-4a4e-9dcd-e34cc2563a37@gmail.com>
Date: Wed, 7 Feb 2024 15:58:41 -0300
From: Martin Rodriguez Reboredo <yakoyoku@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng
 <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...sung.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Arve Hjønnevåg <arve@...roid.com>,
 Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
 Joel Fernandes <joel@...lfernandes.org>, Carlos Llamas
 <cmllamas@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>,
 Dan Williams <dan.j.williams@...el.com>, Kees Cook <keescook@...omium.org>,
 Matthew Wilcox <willy@...radead.org>, Thomas Gleixner <tglx@...utronix.de>
Cc: Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 4/9] rust: cred: add Rust abstraction for `struct cred`

On 2/2/24 07:55, Alice Ryhl wrote:
> From: Wedson Almeida Filho <wedsonaf@...il.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@...il.com>
> Co-developed-by: Alice Ryhl <aliceryhl@...gle.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> [...]
> +    /// 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 };

 From what I can see `file.f_cred` is valid from the moment `file` was
initialized, worth to notice too IMO.

> +
> +        // 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) }
> +    }
> [...]

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>