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A layer normalizes what it captures, but a layer travels through Buck as a directory artifact, and Buck stores no mode beyond the executable bit. A layer materialized from the cache therefore has every directory in the mode the host's umask allows: 0775 under a developer's 0002, 0755 under CI's 0022. sshd refuses a group-writable /usr/share/empty.sshd, so an image built from cached layers on such a host boots without a working SSH server, while CI never sees it. finalize.image() restored /tmp's 1777 as the one mode a layer cannot carry, but left the rest to the layers. Normalize the whole mounted stack there, the last point before the image is written, and only chmod what differs so the overlay copies up nothing it need not. The sysext driver writes /opt and the extension-release after that point, so it normalizes what it creates. layer.py uses the shared function; its test moves to finalize_test.py.
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I have only lightly reviewed this, most is claude. I think this means we can also drop the special case for /tmp, /var/tmp but I leave that to you I wanted to be conservative here.
A layer normalizes what it captures, but a layer travels through Buck as a directory artifact, and Buck stores no mode beyond the executable bit. A layer materialized from the cache therefore has every directory in the mode the host's umask allows: 0775 under a developer's 0002, 0755 under CI's 0022. sshd refuses a group-writable /usr/share/empty.sshd, so an image built from cached layers on such a host boots without a working SSH server, while CI never sees it.
finalize.image() restored /tmp's 1777 as the one mode a layer cannot carry, but left the rest to the layers. Normalize the whole mounted stack there, the last point before the image is written, and only chmod what differs so the overlay copies up nothing it need not. The sysext driver writes /opt and the extension-release after that point, so it normalizes what it creates.
layer.py uses the shared function; its test moves to finalize_test.py.