CVE-2020-15254

Crossbeam is a set of tools for concurrent programming. In
crossbeam-channel before version 0.4.4, the bounded channel incorrectly
assumes that Vec::from_iter has allocated capacity that same as the
number of iterator elements. Vec::from_iter does not actually guarantee
that and may allocate extra memory. The destructor of the bounded channel
reconstructs Vec from the raw pointer based on the incorrect assumes
described above. This is unsound and causing deallocation with the
incorrect capacity when Vec::from_iter has allocated different sizes with
the number of iterator elements. This has been fixed in crossbeam-channel
0.4.4.

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