Make the download() function save the package into a temporary space and
move to the target location only after checking the signature. This is
safer option than requiring all callers to explicitly verify the
signature. Also, make the download() function verify if the template
name inside the package matches what was requested.
Especially, make `qvm-template download` action verify the signature
too.
On `qvm-template install` avoid checking the signature again for
downloaded packages, by passing extra argument to the verify_rpm()
function. But still verify signature of packages loaded from disk.
This makes the package verified against _only_ the key specified in the
repo config, not all the trusted keys.
If repo does not specify a key, use the default one (change this to a
single file, instead of the whole directory). Existing 'gpgkey' entry
pointing at non-existing file will result in an error.
Use fcntl.flock() instead of just file existence check, so it won't fail
on a stale lock file. While at it, move locking to a function decorator,
to de-clutter the install function a bit. This will allow reducing
indentation level, but don't do it yet, to make the patch readable.
Move lock testing into a separate test, and remove it from install
tests.
QubesOS/qubes-issues#2534
Avoid risk of conflicting downloads to the same directory, reusing
partial downloads, leaving broken files etc. Move template package out
of temporary directory only after its verified.
QubesOS/qubes-issues#2534
RPM API is confusing and it's easy to get it wrong when verifying
package signatures.
Call 'rpmkeys --checksig' which is more rebust here - RPM authors should
know how to use their API.
QubesOS/qubes-issues#2534
