linux-kernel - Re: [PATCH] rust: uaccess: use to

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Message-ID: <CAH5fLggt4YJe93xo9KTr=hTQoj28=jjJtaxo=gFmnTbWmm8SRg@mail.gmail.com>
Date: Thu, 21 Aug 2025 13:04:18 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Onur Özkan <work@...rozkan.dev>
Cc: rust-for-linux@...r.kernel.org, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	lossin@...nel.org, a.hindborg@...nel.org, tmgross@...ch.edu, dakr@...nel.org, 
	tamird@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: uaccess: use to_result for error handling

On Thu, Aug 21, 2025 at 11:19 AM Onur Özkan <work@...rozkan.dev> wrote:
>
> Simplifies error handling by replacing the manual check
> of the return value with the `to_result` helper.
>
> Signed-off-by: Onur Özkan <work@...rozkan.dev>
> ---
>  rust/kernel/uaccess.rs | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index a8fb4764185a..9992eece2694 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -7,7 +7,7 @@
>  use crate::{
>      alloc::{Allocator, Flags},
>      bindings,
> -    error::Result,
> +    error::{to_result, Result},
>      ffi::{c_char, c_void},
>      prelude::*,
>      transmute::{AsBytes, FromBytes},
> @@ -495,9 +495,7 @@ fn raw_strncpy_from_user(dst: &mut [MaybeUninit<u8>], src: UserPtr) -> Result<us
>          )
>      };
>
> -    if res < 0 {
> -        return Err(Error::from_errno(res as i32));
> -    }
> +    to_result(res as i32)?;

This is wrong. The type of `res` is isize, and casting a positive
isize to i32 can result in a negative number and incorrectly trigger
this error. For example: 2147483650i64 as i32 is -2147483646.

Alice