linux-kernel - Re: [PATCH] uaccess: rust: add strncpy_from

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Message-ID: <aApniKYrVaDsu60S@pollux>
Date: Thu, 24 Apr 2025 18:32:08 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uaccess: rust: add strncpy_from_user

On Thu, Apr 24, 2025 at 03:17:48PM +0000, Alice Ryhl wrote:
> 
> +/// Reads a nul-terminated string into `buf` and returns the length.
> +///
> +/// Fails with [`EFAULT`] if the read happens on a bad address. If the end of `buf` is reached,
> +/// then the buffer will not be nul-terminated.
> +#[inline]
> +pub fn strncpy_from_user(ptr: UserPtr, buf: &mut [u8]) -> Result<usize> {

Should probably be named strcpy_from_user() instead.

> +    // CAST: Slice lengths are guaranteed to be `<= isize::MAX`.
> +    let len = buf.len() as isize;
> +
> +    // SAFETY: `buf` is valid for writing `buf.len()` bytes.
> +    let res = unsafe {
> +        bindings::strncpy_from_user(
> +            buf.as_mut_ptr(),
> +            ptr as *const u8,

kernel::ffi::c_char should always match u8, but should we use the FFI type
regardless?