Re: [PATCH] ovl: do not ignore disk quota if current task is not privileged

[Konstantin Khlebnikov]

On 10.01.2017 21:11, Amir Goldstein wrote:
> On Tue, Jan 10, 2017 at 6:34 PM, Konstantin Khlebnikov
> <khlebnikov@xxxxxxxxxxxxxx> wrote:
> > On 10.01.2017 18:57, Miklos Szeredi wrote:
> > > On Tue, Jan 10, 2017 at 3:46 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> > > > On Tue, Jan 10, 2017 at 02:26:48PM +0300, Konstantin Khlebnikov wrote:
> > > > > If overlay was mounted by root then quota set for upper layer does not work
> > > > > because overlay now always use mounter's credentials for operations.
> > > > >
> > > > > This patch adds second copy of credentials without CAP_SYS_RESOURCE and
> > > > > use it if current task doesn't have this capability in mounter's user-ns.
> > > > > This affects creation new files, whiteouts, and copy-up operations.
> > > > >
> > > > > Now quota limits are ignored only if both mounter and current task have
> > > > > capability CAP_SYS_RESOURCE in root user namespace.
> > > >
> > > >
> > > > This makes sense to me. I too would like quota to take effect for
> > > > containers on overlay.
> > >
> > >
> > > At first sight I hated this patch.  It breaks the nice concept that
> > > underlying filesystems are just storage for the overlay and don't care
> > > about caller's privileges (as a block device wouldn't care about
> > > caller's privileges when allocating space).
> > >
> > > However I don't see a good way around this, so...
> >
> >
> > Another solution: just always drop CAP_SYS_RESOURCE from capabilities.
>
> That sounds like a better (and simpler) solution.
>
> Let overlayfs support mount options noquota|quota (default configurable
> from Kconfig and module param) and 'quota' means drop CAP_SYS_RESOURCE.

Too complicated for me. Let's drop it unconditionally. See v2 patch.

> > > Looks like this also has effect on reserving space in ext4, not sure
> > > what that entails.
> >
> >
> > Yes, CAP_SYS_RESOURCE allows to use reserved space and inodes.
>
> That's really not good. It's beyond disobeying user quotas, because
> file system may get to unrecoverable state when corruption is detected
> and already filled the root reserved space.
>
> Amir.


--
Konstantin