Re: [PATCH v4] rust: num: restrict bool conversion to unsigned Bounded

On Sat, Aug 22, 2026 at 10:45 AM Younes Akhouayri via B4 Relay
<[email protected]> wrote:
>
> From: Younes Akhouayri <[email protected]>
>
> From<bool> turns true into 1. A signed Bounded with N = 1 can hold
> only -1 and 0. The current implementation can therefore create a value
> that breaks Bounded's invariant. Deref relies on that invariant and
> calls unreachable_unchecked() when it is broken, so safe Rust can reach
> undefined behavior.
>
> The other primitive conversions require the source and destination to
> have the same signedness. Treat bool as an unsigned one-bit value and
> allow conversions between bool and Bounded only when the backing integer
> type is unsigned.
>
> Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
> Closes: https://lore.kernel.org/rust-for-linux/[email protected]/
> Cc: [email protected]
> Suggested-by: Alexandre Courbot <[email protected]>
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Younes Akhouayri <[email protected]>

Applied to `rust-fixes` -- thanks everyone!

Reviewing this with an LLM made me notice that we should probably seal
`Integer` or make it `unsafe`, because currently someone can
buggily/maliciously implement it to still trigger UB regardless of
this fix.

Cheers,
Miguel