google / OpenSK / 38760844894

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github

Improves CTAPHID channel handling (#803)

We solve two issues related to channel ID handling:

- The maximum channel ID problem.
- Incoming messages on the wrong channel ID were rejected late.

Before, channel ID related code was distributed between `mod.rs` and
`receive.rs`. For the above fixes, we would have needed to parse packets
twice. Instead, a small refactoring made responsibilities clearer:
Channel allocation and locking are in `mod.rs` only. This simplifies
some logic in `receive.rs`.

Returning early for invalid channels also improves the error codes.
Now `ERR_INVALID_CHANNEL` does not compete with other potential errors
anymore.

To fix the channel ID overflow problem, we explicitly make allocated
channel IDs wrap now. Maximum channel ID is one before broadcast.
When wrapping happens, we reject all channels until they get
re-initialized. An older channel not timing out client-side and
interfering with a new allocation is unlikely given the number of
possible channels, and could in theory also happen after a reboot, so
this behavior should be acceptible.

277 of 277 new or added lines in 2 files covered. (100.0%)

14016 of 14406 relevant lines covered (97.29%)

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