keyring: Fix a panic when decrypting aead with empty RSA block.

[jrasell]

Description

Clusters that have gone through several upgrades have be found to include keyring material which has an empty RSA block.

In more recent versions of Nomad, an empty RSA block is omitted from being written to disk. This results in the panic not being present. Older versions, however, did not have this struct tag meaning we wrote an empty JSON block which is not accounted for in the current version.

Spot check for this locally in the code:

ag "WrappedRSAKey != nil {"

ag "WrappedRSAKey != nil && "
nomad/encrypter.go
480:		if wrappedKey.WrappedRSAKey != nil && len(wrappedKey.WrappedRSAKey.Ciphertext) > 0 {
808:	if kekWrapper.WrappedRSAKey != nil && len(kekWrapper.WrappedRSAKey.Ciphertext) > 0 {

Links

closes #24441
related #24383

Contributor Checklist

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[pkazmierczak]

LGTM!

[tgross]

LGTM

[devdrik]

Is there a way to manually heal a cluster that ran into this issue?

edit: we have a workaround for this now: we build nomad 1.9.4-dev from source and inject the nomad binary to the servers. They pick up the new version and start working as expected.

[blalor]

Adding to @devdrik's workaround, I grabbed a binary artifact from the latest build action on the releases/1.9.x branch: https://github.com/hashicorp/nomad/actions/workflows/build.yml?query=branch%3Arelease%2F1.9.x (click a run, scroll to "Artifacts").