$ARCH-repodata is currently not protected by a signature. While most of
the package metadata is also embedded into the .xbps files, which are
protected by a signature, xbps-install ignores it
(1670ff000d/lib/package_unpack.c (L123))
and relies entirely on $ARCH-repodata.
This enables anyone who is able to modify the $ARCH-repodata to
substitute packages. This patch adds a check that verifies the signed
pkgver matches the one in the repodata, so at least downgrades posing as
updates are detected.
This is an incomplete fix as the whole transaction is still set up with
the unsigned repodata and other issues surely exist. The real fix is
signing $ARCH-repodata.
4aae026615