From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AB837374E64; Mon, 20 Apr 2026 17:23:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776705795; cv=none; b=u7+8n4H5+rWT7SBaSc/2pMpIdD7R2CU/GFTM9SSt8sCfzR3FRWH552c+rYQ/Ou7ODUwiN1rsAPwe/k57ydzQVVWoNvJB2AUKtXh7qGO8Pr4679hDnoZMjP3vA4OoX3YfFQcOj0UKQBgc9ighsgM23CGFNL0qn6MF9epNWtGjJio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776705795; c=relaxed/simple; bh=RDw+2/yrSekeZqbdwCFumgPFmQPYUffjovp3DYsv3LA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RBVLNOkHT+00++viQV6LJHxPR4kYisREccIHMGhV2CLxPfCD1XhoRiI+GxdIord3dDfYjEQXZHa0cSk39SRf+9CGqd9kfyZ++0gAckWT19g+bnnCZkrjrQpFYjyd47M72cTYPpW9f/bNRUrzpTC9zMQWRba3OS5sO80FObD5XlM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mmzgYtfM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mmzgYtfM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DAE3C19425; Mon, 20 Apr 2026 17:23:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776705795; bh=RDw+2/yrSekeZqbdwCFumgPFmQPYUffjovp3DYsv3LA=; h=From:To:Cc:Subject:Date:Reply-To:From; b=mmzgYtfMfQWefte3Gx+pNWc6RTWzzxAbVPRmRXNPwGd8Sx+K4S67fwftWeAcWYAQR 9PERlPaKyLne2YYld69YVjagqD4jUJKXVNXJUgrGvsfkAjCkyKFAi99OJAzwAIc0tz O2yY1p6y1EuSaRQPXGZE4U+NAsGT2Fh9vpBWSVnCAMQnk7zn4L9zhoA+10D4hobne5 V81eaIBKB33xnPldWVisID2++egQ1VLWQn3ka130345uWaxSd7hbNtYDhwboKFZqCk 6vPApVO33r8WZbkTl5kyvj6rN+LcD2zsqgghbclfzQBD9zeTJCKOawHvIF4FvDrLWz LxC7bPQ4t+tTQ== From: Gary Guo To: Benno Lossin , Gary Guo , Miguel Ojeda , Boqun Feng , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich Cc: stable@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] rust: pin-init: fix incorrect accessor reference lifetime Date: Mon, 20 Apr 2026 18:23:01 +0100 Message-ID: <20260420172302.1843752-1-gary@kernel.org> X-Mailer: git-send-email 2.51.2 Reply-To: Gary Guo Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Gary Guo When a field has been initialized, `init!`/`pin_init!` create a reference or pinned reference to the field so it can be accessed later during the initialization of other fields. However, the reference it created is incorrectly `&'static` rather than just the scope of the initializer. This means that you can do init!(Foo { a: 1, _: { let b: &'static u32 = a; } }) which is unsound. This is caused by `&mut (*#slot).#ident`, which actually allows arbitrary lifetime, so this is effectively `'static`. Somewhat ironically, the safety justification of creating the accessor is.. "SAFETY: TODO". Fix it by adding `Deref`/`DerefMut` implementation to `DropGuard` and derive the reference from dereferencing `DropGuard` instead. The lifetime of `DropGuard` is exactly what we want for these accessors. The old accessor creation code also has a purpose of preventing unaligned fields. So a `let _ = &(*#slot).#ident` still needs to be present, but this no longer has to care about pinning, so it is moved to just before the guard generation. Fixes: 42415d163e5d ("rust: pin-init: add references to previously initialized fields") Cc: stable@vger.kernel.org Signed-off-by: Gary Guo --- The patch is also available at https://github.com/Rust-for-Linux/pin-init/pull/132 which has regression tests added and runs through pin-init's test suite. --- rust/pin-init/internal/src/init.rs | 107 +++++++++++++---------------- rust/pin-init/src/__internal.rs | 27 +++++++- 2 files changed, 73 insertions(+), 61 deletions(-) diff --git a/rust/pin-init/internal/src/init.rs b/rust/pin-init/internal/src/init.rs index daa3f1c6466e..c5f848103c92 100644 --- a/rust/pin-init/internal/src/init.rs +++ b/rust/pin-init/internal/src/init.rs @@ -249,22 +249,6 @@ fn init_fields( }); // Again span for better diagnostics let write = quote_spanned!(ident.span()=> ::core::ptr::write); - // NOTE: the field accessor ensures that the initialized field is properly aligned. - // Unaligned fields will cause the compiler to emit E0793. We do not support - // unaligned fields since `Init::__init` requires an aligned pointer; the call to - // `ptr::write` below has the same requirement. - let accessor = if pinned { - let project_ident = format_ident!("__project_{ident}"); - quote! { - // SAFETY: TODO - unsafe { #data.#project_ident(&mut (*#slot).#ident) } - } - } else { - quote! { - // SAFETY: TODO - unsafe { &mut (*#slot).#ident } - } - }; quote! { #(#attrs)* { @@ -272,51 +256,31 @@ fn init_fields( // SAFETY: TODO unsafe { #write(&raw mut (*#slot).#ident, #value_ident) }; } - #(#cfgs)* - #[allow(unused_variables)] - let #ident = #accessor; } } InitializerKind::Init { ident, value, .. } => { // Again span for better diagnostics let init = format_ident!("init", span = value.span()); - // NOTE: the field accessor ensures that the initialized field is properly aligned. - // Unaligned fields will cause the compiler to emit E0793. We do not support - // unaligned fields since `Init::__init` requires an aligned pointer; the call to - // `ptr::write` below has the same requirement. - let (value_init, accessor) = if pinned { - let project_ident = format_ident!("__project_{ident}"); - ( - quote! { - // SAFETY: - // - `slot` is valid, because we are inside of an initializer closure, we - // return when an error/panic occurs. - // - We also use `#data` to require the correct trait (`Init` or `PinInit`) - // for `#ident`. - unsafe { #data.#ident(&raw mut (*#slot).#ident, #init)? }; - }, - quote! { - // SAFETY: TODO - unsafe { #data.#project_ident(&mut (*#slot).#ident) } - }, - ) + let value_init = if pinned { + quote! { + // SAFETY: + // - `slot` is valid, because we are inside of an initializer closure, we + // return when an error/panic occurs. + // - We also use `#data` to require the correct trait (`Init` or `PinInit`) + // for `#ident`. + unsafe { #data.#ident(&raw mut (*#slot).#ident, #init)? }; + } } else { - ( - quote! { - // SAFETY: `slot` is valid, because we are inside of an initializer - // closure, we return when an error/panic occurs. - unsafe { - ::pin_init::Init::__init( - #init, - &raw mut (*#slot).#ident, - )? - }; - }, - quote! { - // SAFETY: TODO - unsafe { &mut (*#slot).#ident } - }, - ) + quote! { + // SAFETY: `slot` is valid, because we are inside of an initializer + // closure, we return when an error/panic occurs. + unsafe { + ::pin_init::Init::__init( + #init, + &raw mut (*#slot).#ident, + )? + }; + } }; quote! { #(#attrs)* @@ -324,9 +288,6 @@ fn init_fields( let #init = #value; #value_init } - #(#cfgs)* - #[allow(unused_variables)] - let #ident = #accessor; } } InitializerKind::Code { block: value, .. } => quote! { @@ -339,18 +300,46 @@ fn init_fields( if let Some(ident) = kind.ident() { // `mixed_site` ensures that the guard is not accessible to the user-controlled code. let guard = format_ident!("__{ident}_guard", span = Span::mixed_site()); + + // NOTE: The reference is derived from the guard so that it only lives as long as the + // guard does and cannot escape the scope. If it's created via `&mut (*#slot).#ident` + // like the unaligned field guard, it will become effectively `'static`. + let accessor = if pinned { + let project_ident = format_ident!("__project_{ident}"); + quote! { + // SAFETY: the initialization is pinned. + unsafe { #data.#project_ident(&mut *#guard) } + } + } else { + quote! { + &mut *#guard + } + }; + res.extend(quote! { + // Take a reference of the field to ensure that the initialized field is + // properly aligned. Unaligned fields will cause the compiler to emit E0793. We + // do not support unaligned fields since `Init::__init` requires an aligned + // pointer; the call to `ptr::write` above has the same requirement. + // SAFETY: `slot` is valid. + #(#cfgs)* + let _ = unsafe { &(*#slot).#ident }; + #(#cfgs)* // Create the drop guard: // // We rely on macro hygiene to make it impossible for users to access this local // variable. // SAFETY: We forget the guard later when initialization has succeeded. - let #guard = unsafe { + let mut #guard = unsafe { ::pin_init::__internal::DropGuard::new( &raw mut (*slot).#ident ) }; + + #(#cfgs)* + #[allow(unused_variables)] + let #ident = #accessor; }); guards.push(guard); guard_attrs.push(cfgs); diff --git a/rust/pin-init/src/__internal.rs b/rust/pin-init/src/__internal.rs index 90adbdc1893b..d122ab840c44 100644 --- a/rust/pin-init/src/__internal.rs +++ b/rust/pin-init/src/__internal.rs @@ -5,6 +5,8 @@ //! These items must not be used outside of this crate and the pin-init-internal crate located at //! `../internal`. +use core::ops::{Deref, DerefMut}; + use super::*; /// See the [nomicon] for what subtyping is. See also [this table]. @@ -238,6 +240,10 @@ struct Foo { /// When a value of this type is dropped, it drops a `T`. /// /// Can be forgotten to prevent the drop. +/// +/// # Invariants +/// +/// `ptr` is convertible to a mutable reference and `*ptr` is owned by `DropGuard`. pub struct DropGuard { ptr: *mut T, } @@ -259,11 +265,28 @@ pub unsafe fn new(ptr: *mut T) -> Self { } } +impl Deref for DropGuard { + type Target = T; + + #[inline] + fn deref(&self) -> &T { + // SAFETY: `ptr` is convertible to reference + unsafe { &*self.ptr } + } +} + +impl DerefMut for DropGuard { + #[inline] + fn deref_mut(&mut self) -> &mut T { + // SAFETY: `ptr` is convertible to a mutable reference + unsafe { &mut *self.ptr } + } +} + impl Drop for DropGuard { #[inline] fn drop(&mut self) { - // SAFETY: A `DropGuard` can only be constructed using the unsafe `new` function - // ensuring that this operation is safe. + // SAFETY: `DropGuard` owns the `*ptr`. unsafe { ptr::drop_in_place(self.ptr) } } } base-commit: 1c7cc4904160c6fc6377564140062d68a3dc93a0 -- 2.51.2