Let's not make up synthetic errors if the kernel returns a useful error
to us, that tells us about key validity.
Specifically, if we try to activate a dm-verity device with a signed
root hash, it's import to know when we couldn't activate it due to the
signing key missing in the kernel keyring. The kernel reports a nice
error code in that case (ENOKEY), let's make sure this is propagated
back to clients.
To be on the safe side, this allowlists only the three key management
related error codes ENOKEY, EKEYREVOKED, EKEYEXPIRED and returns ENOKEY
for all of them. The kernel's DM stack traditionally wasn't very good
with returning useful error codes, hence the conservative approach.
This patch is not sufficient to fix this properly. There's a patch
needed to fix errno propagation also in libdevmapper:
https://gitlab.com/lvmteam/lvm2/-/merge_requests/3
With both patches applied we get correct error code reporting.
Fixes: #841
20bfec91d8