A verity signature partition carries a JSON object that must be followed by
NUL bytes only, up to the end of the partition (dissect refuses anything
else). The split-out artifact repart generates for it however is trimmed of
that padding since b54ef83414, so that it is a plain JSON text file (which
jq nowadays insists on).
sysupdate installs such a file into a partition by simply writing it at the
partition's offset, leaving whatever follows in place. Hence, once a shorter
signature (e.g. after rotating to a different key type) is installed into a
partition that previously held a longer one, the tail of the old signature
survives right after the new JSON object, and the partition becomes
unparsable.
Add a new PartitionZeroFill= boolean setting to the [Target] section, which
makes the importer continue writing zeroes up to the end of the partition
once the payload has been written, by passing --zero-fill= to systemd-import
and systemd-pull. It defaults to off, except for verity signature partitions
(which are tiny, hence this is cheap) where it defaults to on.
Fixes: #43567
(cherry picked from commit d3b6d765a5b320d6d864591c6a7b87e1047d0c78)
Lennart Poettering
2c4e3b9a6b