Re: [PATCH v5 10/15] rust: init: add `stack_pin_init!` macro

Alice Ryhl
2023-04-03T17:58:01Z

On 4/3/23 18:05, Benno Lossin wrote:
> The `stack_pin_init!` macro allows pin-initializing a value on the
> stack. It accepts a `impl PinInit<T, E>` to initialize a `T`. It allows
> propagating any errors via `?` or handling it normally via `match`.
>
> Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
> Cc: Alice Ryhl <aliceryhl@google.com>
> Cc: Andreas Hindborg <a.hindborg@samsung.com>
> Cc: Gary Guo <gary@garyguo.net>
> ---

If you fix the issue below, then you may add
Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> + /// Initializes the contents and returns the result.
> + #[inline]
> + pub fn init<E>(self: Pin<&mut Self>, init: impl PinInit<T, E>) -> Result<Pin<&mut T>, E> {
> + // SAFETY: We never move out of `this`.
> + let this = unsafe { Pin::into_inner_unchecked(self) };
> + // The value is currently initialized, so it needs to be dropped before we can reuse
> + // the memory (this is a safety guarantee of `Pin`).
> + if this.1 {
> + // SAFETY: `this.1` is true and we set it to false after this.
> + unsafe { this.0.assume_init_drop() };
> + this.1 = false;
> + }

This would double-free the value if `assume_init_drop` panics. I know
that we configure panics to abort the kernel, but someone could copy
this into another codebase and then they would have this issue.

You can fix it by setting `this.1` to false *before* calling
`assume_init_drop`.