RUSTSEC-2020-0048: Use-after-free in BodyStream due to lack of pinning

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Use-after-free in BodyStream due to lack of pinning

Details
Package	actix-http
Version	3.0.0-beta.5
URL	actix/actix-web#1321
Date	2020-01-24
Patched versions	>=2.0.0-alpha.1

Affected versions of this crate did not require the buffer wrapped in BodyStream to be pinned,
but treated it as if it had a fixed location in memory. This may result in a use-after-free.

The flaw was corrected by making the trait MessageBody require Unpin
and making poll_next() function accept Pin<&mut Self> instead of &mut self.

See advisory page for additional details.