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

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Message-Id: <20241123-rust-fix-arraylayout-v1-1-197e64c95bd4@asahilina.net>
Date: Sat, 23 Nov 2024 19:29:38 +0900
From: Asahi Lina <lina@...hilina.net>
To: 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>
Cc: Janne Grunau <j@...nau.net>, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, asahi@...ts.linux.dev, 
 Asahi Lina <lina@...hilina.net>
Subject: [PATCH] rust: alloc: Fix `ArrayLayout` allocations

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