linux-kernel - Re: [PATCH v2 1/4] rust: uaccess: add userspace pointers

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Date: Wed, 21 Feb 2024 12:47:18 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: 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>, 
	Kees Cook <keescook@...omium.org>, Al Viro <viro@...iv.linux.org.uk>, 
	Andrew Morton <akpm@...ux-foundation.org>
Cc: 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>, Arnd Bergmann <arnd@...db.de>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v2 1/4] rust: uaccess: add userspace pointers

On Thu, Feb 8, 2024 at 4:48 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> +    /// Reads the entirety of the user slice, appending it to the end of the
> +    /// provided buffer.
> +    ///
> +    /// Fails with `EFAULT` if the read encounters a page fault.
> +    pub fn read_all(mut self, buf: &mut Vec<u8>) -> Result<()> {
> +        buf.try_reserve(self.length)?;
> +
> +        // SAFETY: The call to `try_reserve` was successful, so the spare
> +        // capacity is at least `self.length` bytes long.
> +        unsafe { self.read_raw(buf.spare_capacity_mut().as_mut_ptr().cast(), self.length)? };
> +
> +        // SAFETY: Since the call to `read_raw` was successful, so the next
> +        // `len` bytes of the vector have been initialized.
> +        unsafe { buf.set_len(buf.len() + self.length) };
> +        Ok(())
> +    }

There's a bug here, since read_raw changes self.length. It will be
fixed in the next version.

Alice