HWPX MIME type is recognized as 'application/zip' with current version of file command (file-5.44).
It will be recognized as 'application/hwp+zip' when new version of file is released.
For a temporary fix, when MIME type of file is 'application/zip',
check the file type again (without the MIME option).
And then check if it's 'Zip data (MIME type "application/hwp+zip"?)' or not.
Only load the LibreOffice extension for opening hwp/hwpx when it is
actually needed. Adding an extension to libreoffice may allow for it to
run arbitrary code. This makes it trust more scalable by trusting
LibreOffice extensions only for the filetypes which they target.
Reasoning
---------
Assuming a malicious `.oxt` extension this means that the extension has
arbitrary code execution in the container. While this is not an
existential threat in itself, we should not expose every Dangerzone user
to it. This is achieved by dynamically loading the extension at runtime
only when needed.
This ensures that a compromised extension will in its least malicious
form be able to modify the visual content of any hancom office files but
not *every file*. In the more malicious version, if the code execution
manages to do a container escape, this will only affect users that have
converted a Hancom office file.
It seems that there are at least two Python libraries with libmagic
support:
* PyPI: python-magic (https://pypi.org/project/python-magic/)
On Fedora it's `python3-magic`
* PyPI: filemagic (https://pypi.org/project/filemagic/)
On Fedora it's `python3-file-magic`
The first package corresponds to the `py3-magic` package on Alpine
Linux, and it's the one we install in the container. The second package
uses a different API, and it's the only one we can use on Qubes.
To make matters worse, we:
* Can't install the first package on Fedora, because it installs the
second under the hood:
https://bugzilla.redhat.com/show_bug.cgi?id=1899279
* Can't install the second package on Alpine Linux (untested), due to
Musl being used instead of libC:
https://stackoverflow.com/a/53936722
Ultimately, we need to support both, by trying the first API, and on
failure using the other API.
The files in `container/` no longer make sense to have that name since
the "document to pixels" part will run in Qubes OS in its own virtual
machine.
To adapt to this, this PR does the following:
- Moves all the files in `container` to `dangerzone/conversion`
- Splits the old `container/dangerzone.py` into its two components
`dangerzone/conversion/{doc_to_pixels,pixels_to_pdf}.py` with a
`common.py` file for shared functions
- Moves the Dockerfile to the project root and adapts it to the new
container code location
- Updates the CircleCI config to properly cache Docker images.
- Updates our install scripts to properly build Docker images.
- Adds the new conversion module to the container image, so that it can
be imported as a package.
- Adapts the container isolation provider to use the new way of calling
the code.
NOTE: We have made zero changes to the conversion code in this commit,
except for necessary imports in order to factor out some common parts.
Any changes necessary for Qubes integration follow in the subsequent
commits.
