Re: [PATCH 0/6] shmem: Add user and group quota support for tmpfs

[Carlos Maiolino <cem@kernel.org>]

On Wed, Apr 05, 2023 at 03:11:22PM +0200, Christian Brauner wrote:
> On Wed, Apr 05, 2023 at 12:44:27PM +0200, Carlos Maiolino wrote:
> > Hi Christian.
> >
> > On Wed, Apr 05, 2023 at 10:52:44AM +0200, Christian Brauner wrote:
> > > On Mon, Apr 03, 2023 at 10:47:53AM +0200, cem@kernel.org wrote:
> > > > From: Carlos Maiolino <cmaiolino@redhat.com>
> > > >
> > > > Hi folks. this work has been done originally by Lukas, but he left the company,
> > > > so I'm taking over his work from where he left it of. This series is virtually
> > > > done, and he had updated it with comments from the last version, but, I'm
> > >
> > > I've commented on the last version:
> > >
> > > https://lore.kernel.org/linux-fsdevel/20221129112133.rrpoywlwdw45k3qa@wittgenstein
> > >
> > > trying to point out that tmpfs can be mounted in user namespaces. Which
> > > means that the quota uids and gids need to take the idmapping of the
> > > user namespace in which the tmpfs instances is mounted in into account;
> > > not the one on the host.
> > >
> > > See the link above for some details. Before we can merge this it would
> > > be very good if we could get tests that verify tmpfs being mounted
> > > inside a userns with quotas enabled because I don't think this is
> > > covered yet by xfstests. Or you punt on it for now and restricted quotas
> > > to tmpfs instances mounted on the host.
> > >
> >
> > Thanks for the link, I've read it before, and this is by now a limitation I'd
> > like to keep in this series. I can extend it to be namespace aware later on, but
> > the current goal of this series is to be able tmpfs mounts on the host to limit
> > the amount of memory consumed by users. Being namespace aware is something I
> 
> This is fine with me. But please point the restriction out in the
> documentation and in the commit message. This is especially important
> because the check is hidden in the bowls of dquot_load_quota_sb().

Sounds reasonable, I'll work on the comments I received and re-send this series
next week if nothing urgent comes up.

> 
> Ideally we'd probably check for fc->user_ns == &init_user_ns directly
> when parsing the quota mount options instead of waiting until
> fill_super.

-- 
Carlos Maiolino