GHSA-pg9f-39pc-qf8g crossbeam-channel Vulnerable to Double Free on Drop

• crates.io crossbeam-channel: >= 0.5.12, < 0.5.15 → fixed in 0.5.15

The internal `Channel` type's `Drop` method has a race which could, in some circumstances, lead to a double-free. This could result in memory corruption. Quoting from the upstream description in merge request \#1187: > The problem lies in the fact that `dicard_all_messages` contained two paths that could lead to `head.block` being read but only one of them would swap the value. This meant that `dicard_all_messages` could end up observing a non-null block pointer (and therefore attempting to free it) without setting `head.block` to null. This would then lead to `Channel::drop` making a second attempt at dropping the same pointer. The bug was introduced while fixing a memory leak, in upstream MR \#1084, first published in 0.5.12. The fix is in upstream MR \#1187 and has been published in 0.5.15