linux-kernel - [PATCH 07/12] rust: pin-init: add `?Sized` bounds to traits in `#[pin

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Message-ID: <20260108135127.3153925-8-lossin@kernel.org>
Date: Thu,  8 Jan 2026 14:50:45 +0100
From: Benno Lossin <lossin@...nel.org>
To: Benno Lossin <lossin@...nel.org>,
	Gary Guo <gary@...yguo.net>,
	Miguel Ojeda <ojeda@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Fiona Behrens <me@...enk.dev>
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 07/12] rust: pin-init: add `?Sized` bounds to traits in `#[pin_data]` macro

The `#[pin_data]` macro uses some auxiliary traits to ensure that a user
does not implement `Drop` for the annotated struct, as that is unsound
and can lead to UB. However, if the struct that is annotated is
`!Sized`, the current bounds do not work, because `Sized` is an implicit
bound for generics.

This is *not* a soundness hole of pin-init, as it currently is
impossible to construct an unsized struct using pin-init.

Signed-off-by: Benno Lossin <lossin@...nel.org>
---
 rust/pin-init/internal/src/pin_data.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/pin-init/internal/src/pin_data.rs b/rust/pin-init/internal/src/pin_data.rs
index d1e7ed121860..0fc0ce5fd4e4 100644
--- a/rust/pin-init/internal/src/pin_data.rs
+++ b/rust/pin-init/internal/src/pin_data.rs
@@ -236,7 +236,7 @@ fn drop(&mut self) {
             // if it also implements `Drop`
             trait MustNotImplDrop {}
             #[expect(drop_bounds)]
-            impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
+            impl<T: ::core::ops::Drop + ?::core::marker::Sized> MustNotImplDrop for T {}
             impl #impl_generics MustNotImplDrop for #ident #ty_generics
                 #whr
             {}
@@ -245,7 +245,7 @@ impl #impl_generics MustNotImplDrop for #ident #ty_generics
             // `PinnedDrop` as the parameter to `#[pin_data]`.
             #[expect(non_camel_case_types)]
             trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
-            impl<T: ::pin_init::PinnedDrop>
+            impl<T: ::pin_init::PinnedDrop + ?::core::marker::Sized>
                 UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
             impl #impl_generics
                 UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for #ident #ty_generics
-- 
2.51.2