Re: [PATCH v5 2/4] fuse: Support fuse filesystems outside of init_user_ns

[Miklos Szeredi]

On Wed, Oct 22, 2014 at 04:24:18PM -0500, 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.

Okay.

> 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.

Maybe I'm being dense, but can someone give a concrete example of such an
attack?

That might also help me understand how exactly user/pid namespaces work...

Patch otherwise looks okay.

Thanks,
Miklos
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