[PATCH proxmox-backup 0/2] Fix Undefined Behavior in Tape Block Header Deallocation

["Max R. Carrara" <m.carrara@proxmox.com>]

Fix Undefined Behavior in Tape Block Header Deallocation - v1
=============================================================

We allocate `BlockHeader` in `pbs-tape` with an alignment equal
to the page size, but because it uses packed / 1-byte alignment
(`#[repr(C, packed)]` to be precise), the compiler will treat it as if
it was allocated with 1-byte alignment.

Miri [0] will flag this as undefined behavior:

    error: Undefined Behavior: incorrect layout on deallocation:
    alloc46398 has size 262144 and alignment 4096, but gave size 262144
    and alignment 1

This is because Rust cares about a memory region's alignment on
deallocation, even if the underlying allocator does not -- hence why
this hasn't actually been a problem for us. Still, there is no guarantee
that this will not change at some point in the future.

This is fixed in patch #1. Patch #2 just renames variables to fit the
new implementation better, which I didn't want to include in patch #1,
as it didn't really fit (and it would make the diff ugly). If you feel
like patch #2 is superfluous, feel free to drop it.

Special thanks to @Robert, who brought this to my attention and totally
managed to nerd-snipe me with this. I have added a respective git
trailer in patch #1.

Testing
-------

Would be great if somebody with a working tape storage could give this a
spin -- miri does not report any UB anymore and the tests we have pass,
but some smoke-testing would nevertheless be appreciated. My virtual
tape library has unfortunately borked itself, and I haven't come around
to un-borking it yet.

[0]: https://github.com/rust-lang/miri

Summary of Changes
------------------


proxmox-backup:

Max R. Carrara (2):
  pbs-tape: fix undefined behavior in block header deallocation
  pbs-tape: rename `buffer` to `header`

 pbs-tape/src/blocked_reader.rs |  58 +++---
 pbs-tape/src/blocked_writer.rs |  47 ++---
 pbs-tape/src/lib.rs            | 352 +++++++++++++++++++++++++++------
 3 files changed, 346 insertions(+), 111 deletions(-)


Summary over all repositories:
  3 files changed, 346 insertions(+), 111 deletions(-)

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