A fresh chroot download failed with mmdebstrap unable to copy the
keyrings: its unshare-mode hooks run under an identity that cannot
read the invoking user's private directories, so the 0700 cache
directory the module created broke the trusted.gpg.d setup hook with
'Permission denied' (builds reusing an already-cached tarball never
hit the path).
Create the cache 0755 and chmod the keyrings 0644 instead. The
planting guard does not weaken: cached keyrings are trusted as-is,
and validate_keyring_dir keeps refusing directories that are not
owned by the current user or are writable by group or others — read
access for the bootstrap tool is not a planting vector. Legacy 0700
cache directories are validated as before, then widened.
vhaudiquet
bb719e7c80