Re: [PATCH v2] fs/ceph/quota: ignore quota with CAP_SYS_RESOURCE

[Xiubo Li]

On 9/12/24 04:14, Patrick Donnelly wrote:
> On Wed, Sep 11, 2024 at 3:21 PM Max Kellermann <max.kellermann@xxxxxxxxx> wrote:
> > On Wed, Sep 11, 2024 at 8:04 PM Patrick Donnelly <pdonnell@xxxxxxxxxx> wrote:
> > > CephFS has many components that are cooperatively maintained by the
> > > MDS **and** the clients; i.e. the clients are trusted to follow the
> > > protocols and restrictions in the file system. For example,
> > > capabilities grant a client read/write permissions on an inode but a
> > > client could easily just open any file and write to it at will. There
> > > is no barrier preventing that misbehavior.
> > To me, that sounds like you confirm my assumption on how Ceph works -
> > both file permissions and quotas. As a superuser (CAP_DAC_OVERRIDE), I
> > can write arbitrary files, and just as well CAP_SYS_RESOURCE should
> > allow me to exceed quotas - that's how both capabilities are
> > documented.
> >
> > > Having root on a client does not extend to arbitrary superuser
> > > permissions on the distributed file system. Down that path lies chaos
> > > and inconsistency.
> > Fine for me - I'll keep my patch in our kernel fork (because we need
> > the feature), together with the other Ceph patches that were rejected.
> If you want to upstream this, the appropriate change would go in
> ceph.git as a new cephx capability (not cephfs capability) for the
> "mds" auth cap that would allow a client with root (or
> CAP_SYS_RESOURCE) to bypass quotas. I would support merging such a
> patch (and the corresponding userspace / kernel client changes).
Yeah, Patrick is correct. This really will by pass the protocols and 
restrictions in cephfs and introduces inconsistency. By adding a new 
cephx caps we can broadcast this to all the users or clients.

Thanks