Re: [PATCH v2] rust: num: seal Integer

[Alexandre Courbot]

On Sun Sep 6, 2026 at 12:16 AM JST, Younes Akhouayri via B4 Relay wrote:
> From: Younes Akhouayri <git@xxxxxxxxx>
>
> Bounded relies on Integer implementations to describe primitive integer
> semantics correctly. In particular, it uses Integer::BITS and Signedness
> to justify unchecked operations.
>
> Integer is currently safe and externally implementable, so an
> implementation can violate those assumptions and make safe Bounded
> operations reach undefined behavior.
>
> For example, an Integer implementation for a u8 wrapper can report
> BITS = 16. Safe code can then cast a Bounded<u16, 9> containing 256
> to that wrapper. Its TryFrom<u16> implementation returns Err, and
> Bounded::cast() calls unwrap_unchecked() on it, causing undefined
> behavior.
>
> Seal Integer so only the primitive implementations provided by the
> kernel crate can satisfy it.
>
> Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
> Reported-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
> Closes: https://lore.kernel.org/rust-for-linux/CANiq72mOfR33s4y+Ueivd5NrC5yre+Pcp57ZOBz0msw9A4AP1Q@xxxxxxxxxxxxxx/
> Cc: stable@xxxxxxxxxxxxxxx
> Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
> Signed-off-by: Younes Akhouayri <git@xxxxxxxxx>

Acked-by: Alexandre Courbot <acourbot@xxxxxxxxxx>

Thanks for taking care of this!