Re: [PATCH v4 2/5] fuse: Support fuse filesystems outside of init_user_ns

[Seth Forshee]

On Wed, Oct 15, 2014 at 07:49:39AM -0700, Andy Lutomirski wrote:
> On 10/14/2014 07:25 AM, Seth Forshee wrote:
> > Update fuse to translate uids and gids to/from the user namspace
> > of the process servicing requests on /dev/fuse. Any ids which do
> > not map into the namespace will result in errors. inodes will
> > also be marked bad when unmappable ids are received from
> > userspace.
> > 
> > Due to security concerns the namespace used should be fixed,
> > otherwise a user might be able to gain elevated privileges or
> > influence processes that the user would otherwise be unable to
> > manipulate. Thus the namespace of the mounting process is used
> > for all translations, and this namespace is required to be the
> > same as the one in use when /dev/fuse was opened.
> > 
> 
> I'm not sure that this is necessary if my nosuid patch goes in, but I
> also don't think it makes any sense to hold this up while we find a
> perfect solution.
> 
> Is there a decent way to extend this to different translation schemes in
> the future (e.g. a flag at fs setup that could be used)?

I think it would be possible to relax the translation scheme
restrictions in the future, certainly that's easier than tightening down
a looser restriction. I still favor picking one namespace to use for
translation (surely that's how it would work with other filesystems
anyway) rather than using the current namespace during /dev/fuse I/O. I
did an implementation using the latter technique, and it's far more
complex with no benefits that I can see.

Thanks,
Seth
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