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References: <20240208-alice-mm-v2-0-d821250204a6@google.com> <20240208-alice-mm-v2-1-d821250204a6@google.com>
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From: Alice Ryhl <aliceryhl@google.com>
Date: Wed, 21 Feb 2024 12:47:18 +0100
Message-ID: <CAH5fLgj--WrkLJLG69P59mxBjZvMqTMHjVCcbk3Q4z7ZFTeTRQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] rust: uaccess: add userspace pointers
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>, 
	=?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, 
	Benno Lossin <benno.lossin@proton.me>, Andreas Hindborg <a.hindborg@samsung.com>, 
	Kees Cook <keescook@chromium.org>, Al Viro <viro@zeniv.linux.org.uk>, 
	Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <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>, Arnd Bergmann <arnd@arndb.de>, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, 
	Christian Brauner <brauner@kernel.org>
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On Thu, Feb 8, 2024 at 4:48=E2=80=AFPM Alice Ryhl <aliceryhl@google.com> wr=
ote:
> +    /// 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 spar=
e
> +        // capacity is at least `self.length` bytes long.
> +        unsafe { self.read_raw(buf.spare_capacity_mut().as_mut_ptr().cas=
t(), self.length)? };
> +
> +        // SAFETY: Since the call to `read_raw` was successful, so the n=
ext
> +        // `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