GHSA-rxhx-9fj6-6h2m enum_map macro can cause UB when `Enum` trait is incorrectly implemented

• crates.io enum-map: >= 2.0.0-2, < 2.0.2 → fixed in 2.0.2

Affected versions of this crate did not properly check the length of an enum when using `enum_map!` macro, trusting user-provided length. When the `LENGTH` in the `Enum` trait does not match the array length in the `EnumArray` trait, this can result in the initialization of the enum map with uninitialized types, which in turn can allow an attacker to execute arbitrary code. This problem can only occur with a manual implementation of the Enum trait, it will never occur for enums that use `#[derive(Enum)]`. Example code that triggers this vulnerability looks like this: ```rust enum E { A, B, C, } impl Enum for E { const LENGTH: usize = 2; fn from_usize(value: usize) -> E { match value { 0 => E::A, 1 => E::B, 2 => E::C, _ => unimplemented!(), } } fn into_usize(self) -> usize { self as usize } } impl EnumArray for E { type Array = [V; 3]; } let _map: EnumMap = enum_map! { _ => "Hello, world!".into() }; ``` The flaw was corrected in commit b824e23 by putting `LENGTH` property on sealed trait for macro to read.