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rust: pin-init: make [pin_]chain unwind safe

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Add a drop guard before the call to the chained closure so that the value
initialized by the first stage is dropped if the closure errors or panics;
`mem::forget` the guard on success.

The previous code only ran cleanup on the explicit error path, leaking the
first-stage value if the chained closure panicked.

Reported-by: Gary Guo <gary@garyguo.net>
Closes: https://github.com/Rust-for-Linux/pin-init/issues/136
Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Mirko Adzic <adzicmirko97@gmail.com>
Link: https://patch.msgid.link/20260710-pin-init-sync-v1-7-8fa16cde87ae@garyguo.net
[ Fix Clippy missing safety comment false positive when `slot` and `guard`
  creation are merged in a single line. - Gary ]
Signed-off-by: Gary Guo <gary@garyguo.net>
This commit is contained in:
Mirko Adzic
2026-07-10 17:20:37 +01:00
committed by Gary Guo
parent 7e4d9c946d
commit 0c20f77a26
1 changed files with 10 additions and 12 deletions
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22
rust/pin-init/src/lib.rs
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@@ -959,13 +959,11 @@ unsafe impl<T: ?Sized, E, I, F> PinInit<T, E> for ChainPinInit<I, F, T, E>
{
unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
// SAFETY: All requirements fulfilled since this function is `__pinned_init`.
unsafe { self.0.__pinned_init(slot)? };
// SAFETY: The above call initialized `slot` and we still have unique access.
let val = unsafe { &mut *slot };
// SAFETY: `slot` is considered pinned.
let val = unsafe { Pin::new_unchecked(val) };
// SAFETY: `slot` was initialized above.
(self.1)(val).inspect_err(|_| unsafe { core::ptr::drop_in_place(slot) })
let slot = unsafe { __internal::Slot::<__internal::Pinned, _>::new(slot) };
let mut guard = slot.init(self.0)?;
(self.1)(guard.let_binding())?;
core::mem::forget(guard);
Ok(())
}
}
@@ -1065,11 +1063,11 @@ unsafe impl<T: ?Sized, E, I, F> Init<T, E> for ChainInit<I, F, T, E>
{
unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
// SAFETY: All requirements fulfilled since this function is `__init`.
unsafe { self.0.__pinned_init(slot)? };
// SAFETY: The above call initialized `slot` and we still have unique access.
(self.1)(unsafe { &mut *slot }).inspect_err(|_|
// SAFETY: `slot` was initialized above.
unsafe { core::ptr::drop_in_place(slot) })
let slot = unsafe { __internal::Slot::<__internal::Unpinned, _>::new(slot) };
let mut guard = slot.init(self.0)?;
(self.1)(guard.let_binding())?;
core::mem::forget(guard);
Ok(())
}
}