linux-kernel - Re: [PATCH] rust: alloc: Fix `ArrayLayout` allocations

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Message-ID: <CAEg-Je-rfJkPsR71W-ppcxZg+JJ_qZerx6rjOwMKXBUdKC7V5Q@mail.gmail.com>
Date: Sat, 23 Nov 2024 05:47:42 -0500
From: Neal Gompa <neal@...pa.dev>
To: Asahi Lina <lina@...hilina.net>
Cc: Danilo Krummrich <dakr@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, 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>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Janne Grunau <j@...nau.net>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	asahi@...ts.linux.dev
Subject: Re: [PATCH] rust: alloc: Fix `ArrayLayout` allocations

On Sat, Nov 23, 2024 at 5:30 AM Asahi Lina <lina@...hilina.net> wrote:
>
> We were accidentally allocating a layout for the *square* of the object
> size due to a variable shadowing mishap.
>
> Fixes memory bloat and page allocation failures in drm/asahi.
>
> Reported-by: Janne Grunau <j@...nau.net>
> Fixes: 9e7bbfa18276 ("rust: alloc: introduce `ArrayLayout`")
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---
>  rust/kernel/alloc/layout.rs | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/rust/kernel/alloc/layout.rs b/rust/kernel/alloc/layout.rs
> index 7e0c2f46157b772248450a77ff445091e17fdfd7..4b3cd7fdc816c158e63ac74014cbfc0794547e81 100644
> --- a/rust/kernel/alloc/layout.rs
> +++ b/rust/kernel/alloc/layout.rs
> @@ -45,7 +45,7 @@ pub const fn empty() -> Self {
>      /// When `len * size_of::<T>()` overflows or when `len * size_of::<T>() > isize::MAX`.
>      pub const fn new(len: usize) -> Result<Self, LayoutError> {
>          match len.checked_mul(core::mem::size_of::<T>()) {
> -            Some(len) if len <= ISIZE_MAX => {
> +            Some(size) if size <= ISIZE_MAX => {
>                  // INVARIANT: We checked above that `len * size_of::<T>() <= isize::MAX`.
>                  Ok(Self {
>                      len,
>
> ---
> base-commit: b2603f8ac8217bc59f5c7f248ac248423b9b99cb
> change-id: 20241123-rust-fix-arraylayout-0b1009d89fb7
>
> Cheers,
> ~~ Lina
>
>

The joy of logic bugs. :(

Reviewed-by: Neal Gompa <neal@...pa.dev>


-- 
真実はいつも一つ！/ Always, there's only one truth!