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

[Patrick Donnelly]

On Wed, Sep 11, 2024 at 11:23 AM Max Kellermann
<max.kellermann@xxxxxxxxx> wrote:
>
> On Wed, Sep 11, 2024 at 5:03 PM Patrick Donnelly <pdonnell@xxxxxxxxxx> wrote:
> > Just because the client cooperatively maintains the quota limits with
> > the MDS does not mean it can override the quota in a distributed
> > system.
>
> I thought Ceph's quotas were implemented only on the client, just like
> file permissions. Is that not correct? Is there an additional
> server-side quota check? In my tests, I never saw one; it looked like
> I could write arbitrary amounts of data with my patch.

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.

Having root on a client does not extend to arbitrary superuser
permissions on the distributed file system. Down that path lies chaos
and inconsistency.

-- 
Patrick Donnelly, Ph.D.
He / Him / His
Red Hat Partner Engineer
IBM, Inc.
GPG: 19F28A586F808C2402351B93C3301A3E258DD79D