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

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Message-ID: <aAtZq4KX79TaKEIf@google.com>
Date: Fri, 25 Apr 2025 09:45:15 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.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>, 
	Danilo Krummrich <dakr@...nel.org>, 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 06:38:52PM +0200, Miguel Ojeda wrote:
> On Thu, Apr 24, 2025 at 5:18 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > +    if res < 0 {
> > +        Err(Error::from_errno(res as i32))
> > +    } else {
> > +        #[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]
> > +        assert!(res <= len);
> > +        Ok(res as usize)
> > +    }
> 
> What about:
> 
>     if res < 0 {
>         return Err(...);
>     }
> 
>     overflow_assert!(res <= len);
>     Ok(res as usize)
> 
> That follows a bit better what is usually done on the C side, in using
> early returns (especially for error paths) and in avoiding local
> `#ifdef`s.

Sure, that looks good to me.

> Of course, we can leave this `overflow_assert!` to a different patch
> later on with this code as an example use case, or a good first issue
> etc. It also allows to document it etc. Happy to send it or create the
> issue.
> 
> (I wrote that instead of `assert_overflow!` because it follows the
> `{static,debug}_assert!` patterns, i.e. it changes more the "kind" of
> assert rather than asserting a particular thing, like `_eq!` or
> `_same_type!`).

Sounds like a good good-first-issue.

Alice