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Date: Thu, 24 Apr 2025 18:32:08 +0200
From: Danilo Krummrich <dakr@kernel.org>
To: Alice Ryhl <aliceryhl@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Trevor Gross <tmgross@umich.edu>, rust-for-linux@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] uaccess: rust: add strncpy_from_user
Message-ID: <aApniKYrVaDsu60S@pollux>
References: <20250424-strncpy-from-user-v1-1-f983fe21685a@google.com>
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In-Reply-To: <20250424-strncpy-from-user-v1-1-f983fe21685a@google.com>

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?