[v12] fix: avoid inadvertent deletion of active HSM keys #25208
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This is a partial fix for #25017 The latest version of the YubiHSM2 SDK has changed the behavior for keys longer than 2 bytes, which used to be silently truncated for all operations. This causes an unfortunate interaction with `DeleteUnusedKeys` when the SDK is upgraded in an active Teleport cluster. Because none of the active keys can be queried from the HSM individually by their ID, but they can be listed by their label, all of the active keys end up being deleted. Yeah that's bad. `DeleteUnusedKeys` is written this way in an attempt to be "stateless". Trying to synchronously delete keys at the instant they are rotated out during a CA rotation would be error-prone. If the auth server were to restart or crash at the wrong moment, you could be left with an orphaned key on your HSM forever, with no reference to it stored by Teleport or anywhere else. Instead, the Auth server labels all keys it creates with its own host UUID. Then periodically (during startup) it lists all keys in the HSM that are labeled with its own UUID, and if they are not currently active, deletes them. This goes catastrophically wrong when individual lookup operations fail, but list operations succeed. The fix here is to avoid deleting any keys if any single lookup fails. The YubiHSM2 SDK version 2023.1 is still not supported, but with this fix at least we won't delete any active keys.
AntonAM
approved these changes
Apr 26, 2023
codingllama
approved these changes
Apr 26, 2023
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Backport #25025 to branch/v12