Re: Why not make kdbus use CUSE?

From: Greg Kroah-Hartman
Date: Tue Dec 02 2014 - 12:26:18 EST

On Tue, Dec 02, 2014 at 07:22:11AM -0500, Richard Yao wrote:
> Assuming that this dance succeeds, the FUSE process could then make a
> readonly file in itself, open it read only, unlink it, put the data into
> the file and send the file descriptor via UNIX domain socket while
> refusing further writes. If it has its own user/group, the file should
> be safe from prying eyes.
> This is not as good as a memfd and also suffers from the race that
> O_TMPFILE was meant to close, but it should be able to function as a
> decent fallback.

We can't knowingly create and advocate for broken code, sorry.

> This would preserve portability across not only
> different versions of Linux, but also other POSIX systems.

I honestly do not care about any other system than Linux, so I don't see
why this would ever be an issue.

> Keeping the code in userspace would allow us to apply SELinux policies
> to it, which is something that we would lose if it were go to into the
> kernel.

On the contrary, the kdbusfs implementation gives you better security
model support than before, it ties directly into the LSM hooks, see the
add-on patches from some other developers that bring full support of LSM
to the codebase.

> That said, it is still not clear to me that dbus must be inside the
> kernel to be able to perform multicast and zero copy using memfd.

It seems you have yet to read my introductory email for the patch

greg k-h
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