Re: [PATCH v2 2/2] namespaces: add transparent user namespaces

From: MickaÃl SalaÃn
Date: Tue Jul 12 2016 - 16:19:07 EST


I have been looking for this kind of feature for StemJail [1]. One of the main idea is to being able to create mount points inside a jail as an unprivileged user but to keep as much as possible the same environment from outside the jail. For now, I can only create a mapping for the current user, so when a process list any files belonging to another user/group it get "nobody", which seems weird from a user point of view :)



On 27/06/2016 17:09, Eric W. Biederman wrote:
> Added a few more relevant cc's.
> Jann Horn <jannh@xxxxxxxxxx> writes:
>> This allows the admin of a user namespace to mark the namespace as
>> transparent. All other namespaces, by default, are opaque.
> I have just skimmed through this and at a high level this doesn't seem
> too scary. Having an identity mapped user namespace that just limits
> you to using a subset of uids and gids while allowing displaying the
> full range of uids and gids.
> I don't quite get the use case and I would like to a little better
> but in the long term this shouldn't cause any significant maintenance
> issues, so I don't have any objects.
> At the same time this isn't quite the time to merge this. I am in the
> process of slowly going through Seth's vfs changes to support things
> such as truly unprivileged fuse support. Those changes alter which
> places can always be assumed to be init_user_ns (many fewer), and also
> slightly change the set of from_kuid calls being made.
> The changes that have made it through my review currently reside at:
> git:// for-next
> Those vfs changes make it conceivable and simple from an infrastructure
> standpoint to transition fileystems to unprivileged user namespace
> mounts, with perhaps as little work as just setting FS_USER_NS. At the
> same time that won't be recommend because of the difficulty verifying
> evil filesystem contents can't cause fs implementations to do bad things
> is difficult.
> That change means your first patch that just zaps all from_kuid_munged
> users in init_user_ns isn't a particularly good idea. I don't think it
> is a good idea to have one set of rules for things that will always be
> init_user_ns and another set of rules for code that will change.
> The long and short of this is I am asking you to wait a week or so and
> rebase this on my for-next branch so that we can confirm this change
> interacts nicely will all of the other on-going work.
> Thank you,
> Eric Biederman
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