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FuturesUnordered: fix partial iteration #2574

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wfraser
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@wfraser wfraser commented Feb 23, 2022

The IntoIter impl advances the head pointer every iteration, but this breaks the linked list invariant that the head's prev should be null.

If the iteration is not done to completion (which sets head to null), on subsequent drop, FuturesUnordered::unlink relies on this broken invariant and ends up panicking.

The fix is to maintain the head->prev == null invariant while iterating.

Fixes #2573

@wfraser wfraser requested a review from taiki-e as a code owner February 23, 2022 08:13
@wfraser wfraser force-pushed the futuresunordered-partial-iter-bugfix branch from 904ac08 to d76b9f8 Compare February 23, 2022 08:18
The IntoIter impl advances the head pointer every iteration, but this breaks the linked list invariant that the head's prev should be null.

If the iteration is not done to completion, on subsequent drop, FuturesUnordered::unlink relies on this broken invariant and ends up panicking.

The fix is to maintain the `head->prev == null` invariant while iterating. Also added a test for this bug.
@wfraser wfraser force-pushed the futuresunordered-partial-iter-bugfix branch from d76b9f8 to 108e569 Compare February 23, 2022 08:33
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Thanks!

@taiki-e taiki-e added 0.3-backport: pending The maintainer accepted to backport this to the 0.3 branch, but backport has not been done yet. A-stream Area: futures::stream labels Feb 23, 2022
@taiki-e taiki-e merged commit 391d89e into rust-lang:master Feb 23, 2022
taiki-e pushed a commit that referenced this pull request Aug 14, 2022
The IntoIter impl advances the head pointer every iteration, but this breaks the linked list invariant that the head's prev should be null.

If the iteration is not done to completion, on subsequent drop, FuturesUnordered::unlink relies on this broken invariant and ends up panicking.

The fix is to maintain the `head->prev == null` invariant while iterating. Also added a test for this bug.
@taiki-e taiki-e mentioned this pull request Aug 14, 2022
@taiki-e taiki-e added 0.3-backport: completed and removed 0.3-backport: pending The maintainer accepted to backport this to the 0.3 branch, but backport has not been done yet. labels Aug 14, 2022
taiki-e pushed a commit that referenced this pull request Aug 14, 2022
The IntoIter impl advances the head pointer every iteration, but this breaks the linked list invariant that the head's prev should be null.

If the iteration is not done to completion, on subsequent drop, FuturesUnordered::unlink relies on this broken invariant and ends up panicking.

The fix is to maintain the `head->prev == null` invariant while iterating. Also added a test for this bug.
@taiki-e taiki-e mentioned this pull request Aug 14, 2022
crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Aug 23, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [futures](https://github.com/rust-lang/futures-rs) | dependencies | patch | `0.3.21` -> `0.3.23` |

---

### Release Notes

<details>
<summary>rust-lang/futures-rs</summary>

### [`v0.3.23`](https://github.com/rust-lang/futures-rs/blob/HEAD/CHANGELOG.md#&#8203;0323---2022-08-14)

[Compare Source](rust-lang/futures-rs@0.3.22...0.3.23)

-   Work around MSRV increase due to a cargo bug.

### [`v0.3.22`](https://github.com/rust-lang/futures-rs/blob/HEAD/CHANGELOG.md#&#8203;0322---2022-08-14)

[Compare Source](rust-lang/futures-rs@0.3.21...0.3.22)

-   Fix `Sync` impl of `BiLockGuard` ([#&#8203;2570](rust-lang/futures-rs#2570))
-   Fix partial iteration in `FuturesUnordered` ([#&#8203;2574](rust-lang/futures-rs#2574))
-   Fix false detection of inner panics in `Shared` ([#&#8203;2576](rust-lang/futures-rs#2576))
-   Add `Mutex::lock_owned` and `Mutex::try_lock_owned` ([#&#8203;2571](rust-lang/futures-rs#2571))
-   Add `io::copy_buf_abortable` ([#&#8203;2507](rust-lang/futures-rs#2507))
-   Remove `Unpin` bound from `TryStreamExt::into_async_read` ([#&#8203;2599](rust-lang/futures-rs#2599))
-   Make `run_until_stalled` handle self-waking futures ([#&#8203;2593](rust-lang/futures-rs#2593))
-   Use `FuturesOrdered` in `try_join_all` ([#&#8203;2556](rust-lang/futures-rs#2556))
-   Fix orderings in `LocalPool` waker ([#&#8203;2608](rust-lang/futures-rs#2608))
-   Fix `stream::Chunk` adapters size hints ([#&#8203;2611](rust-lang/futures-rs#2611))
-   Add `push_front` and `push_back` to `FuturesOrdered` ([#&#8203;2591](rust-lang/futures-rs#2591))
-   Deprecate `FuturesOrdered::push` in favor of `FuturesOrdered::push_back` ([#&#8203;2591](rust-lang/futures-rs#2591))
-   Performance improvements ([#&#8203;2583](rust-lang/futures-rs#2583), [#&#8203;2626](rust-lang/futures-rs#2626))
-   Documentation improvements ([#&#8203;2579](rust-lang/futures-rs#2579), [#&#8203;2604](rust-lang/futures-rs#2604), [#&#8203;2613](rust-lang/futures-rs#2613))

</details>

---

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🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

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---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzMi4xNTYuMSIsInVwZGF0ZWRJblZlciI6IjMyLjE1Ni4xIn0=-->

Co-authored-by: cabr2-bot <cabr2.help@gmail.com>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1507
Reviewed-by: crapStone <crapstone@noreply.codeberg.org>
Co-authored-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
Co-committed-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
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Attempt to subtract with overflow in FuturesUnordered's IntoIter after calling .take(n)
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