Re: [PATCH 2/2] rust: alloc: add missing invariant in Vec::set_len()

[Danilo Krummrich <dakr@kernel.org>]

On Sat, Mar 15, 2025 at 04:43:02PM +0100, Danilo Krummrich wrote:
> When setting a new length, we have to justify that the set length
> represents the exact number of elements stored in the vector.
> 
> Fixes: 2aac4cd7dae3 ("rust: alloc: implement kernel `Vec` type")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

[1] probably justifies

	Reported-by: Alice Ryhl <aliceryhl@google.com>

[1] https://lore.kernel.org/rust-for-linux/20250311-iov-iter-v1-4-f6c9134ea824@google.com/

> ---
>  rust/kernel/alloc/kvec.rs | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index 8540d9e2b717..0a4681ad4ce9 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -195,6 +195,9 @@ pub fn len(&self) -> usize {
>      #[inline]
>      pub unsafe fn set_len(&mut self, new_len: usize) {
>          debug_assert!(new_len <= self.capacity());
> +
> +        // INVARIANT: By the safety requirements of this method `new_len` represents the exact
> +        // number of elements stored within `self`.
>          self.len = new_len;
>      }
>  
> -- 
> 2.48.1
>