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Restrict MaybeUninit trait impls to fix soundness #309

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Sep 2, 2023
Merged

Restrict MaybeUninit trait impls to fix soundness #309

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4 changes: 2 additions & 2 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@
[package]
edition = "2021"
name = "zerocopy"
version = "0.6.3"
version = "0.6.4"
authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
description = "Utilities for zero-copy parsing and serialization"
license = "BSD-2-Clause"
Expand All @@ -38,7 +38,7 @@ simd-nightly = ["simd"]
__internal_use_only_features_that_work_on_stable = ["alloc", "simd"]

[dependencies]
zerocopy-derive = { version = "=0.6.3", path = "zerocopy-derive" }
zerocopy-derive = { version = "=0.6.4", path = "zerocopy-derive" }

[dependencies.byteorder]
version = "1.3"
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14 changes: 12 additions & 2 deletions src/lib.rs
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Expand Up @@ -870,11 +870,21 @@ safety_comment! {
//
/// SAFETY:
/// - `FromBytes`: `MaybeUninit<T>` has no restrictions on its contents.
/// Unfortunately, in addition to bit validity, `FromZeroes` and
/// `FromBytes` also require that implementers contain no `UnsafeCell`s.
/// Thus, we require `T: FromZeroes` and `T: FromBytes` in order to ensure
/// that `T` - and thus `MaybeUninit<T>` - contains to `UnsafeCell`s.
/// Thus, requiring that `T` implement each of these traits is sufficient
/// - `Unaligned`: `MaybeUninit<T>` is guaranteed by its documentation [1]
/// to have the same alignment as `T`.
///
/// [1] https://doc.rust-lang.org/nightly/core/mem/union.MaybeUninit.html#layout-1
unsafe_impl!(T => FromBytes for MaybeUninit<T>);
///
/// TODO(https://github.com/google/zerocopy/issues/251): If we split
/// `FromBytes` and `RefFromBytes`, or if we introduce a separate
/// `NoCell`/`Freeze` trait, we can relax the trait bounds for `FromZeroes`
/// and `FromBytes`.
unsafe_impl!(T: FromBytes => FromBytes for MaybeUninit<T>);
unsafe_impl!(T: Unaligned => Unaligned for MaybeUninit<T>);
assert_unaligned!(MaybeUninit<()>, MaybeUninit<u8>);
}
Expand Down Expand Up @@ -4008,7 +4018,7 @@ mod tests {
assert_impls!(ManuallyDrop<[NotZerocopy]>: !FromBytes, !AsBytes, !Unaligned);

assert_impls!(MaybeUninit<u8>: FromBytes, Unaligned, !AsBytes);
assert_impls!(MaybeUninit<NotZerocopy>: FromBytes, !AsBytes, !Unaligned);
assert_impls!(MaybeUninit<NotZerocopy>: !FromBytes, !AsBytes, !Unaligned);

assert_impls!(Wrapping<u8>: FromBytes, AsBytes, Unaligned);
assert_impls!(Wrapping<NotZerocopy>: !FromBytes, !AsBytes, !Unaligned);
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2 changes: 1 addition & 1 deletion zerocopy-derive/Cargo.toml
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Expand Up @@ -5,7 +5,7 @@
[package]
edition = "2021"
name = "zerocopy-derive"
version = "0.6.3"
version = "0.6.4"
authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
description = "Custom derive for traits from the zerocopy crate"
license = "BSD-2-Clause"
Expand Down