Ubuntu's Server Installer Leaked Encrypted Storage Passphrase to Its Log

https://github.com/CanonicalLtd/subiquity/commit/7db70650fea...

I was a little surprised by how it did so just by adding a function, so I looked briefly into how the serialization seems to work.

The FileSystemModel holds a numbers of actions, which it renders[0] into a config for the Curtin program. Part of this process consists of converting instances of various classes into dicts[1] (which presumably become JSON later on). This config is written to various files in /var/log/installer/ during setup.

The conversion into dicts is highly dynamic: it looks up all the fields of the object to be converted, and for each field looks for a "serialize_<field_name>" function on the object. If such a function is present, it is used to serialize the field. If not, the field is typically serialized using its literal value.

One such action class is DM_Crypt[2], which has a "key" field containing the secret. With this commit, the serialize_key() function will be used to write the key itself into a temporary file, and only store the location of the file into the config.

0: https://github.com/CanonicalLtd/subiquity/blob/7db70650feaf5...

1: https://github.com/CanonicalLtd/subiquity/blob/7db70650feaf5...

2: https://github.com/CanonicalLtd/subiquity/blob/7db70650feaf5...