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Date: Tue, 3 Mar 2020 12:56:51 +0100
From: Christian Brauner <christian.brauner@...ntu.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: David Howells <dhowells@...hat.com>, Ian Kent <raven@...maw.net>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Steven Whitehouse <swhiteho@...hat.com>,
Miklos Szeredi <mszeredi@...hat.com>,
viro <viro@...iv.linux.org.uk>,
Christian Brauner <christian@...uner.io>,
Jann Horn <jannh@...gle.com>,
"Darrick J. Wong" <darrick.wong@...cle.com>,
Linux API <linux-api@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
lkml <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver
#17]
On Tue, Mar 03, 2020 at 12:33:48PM +0100, Miklos Szeredi wrote:
> On Tue, Mar 3, 2020 at 11:25 AM Christian Brauner
> <christian.brauner@...ntu.com> wrote:
> >
> > On Tue, Mar 03, 2020 at 11:13:50AM +0100, Miklos Szeredi wrote:
> > > On Tue, Mar 3, 2020 at 11:00 AM Christian Brauner
> > > <christian.brauner@...ntu.com> wrote:
>
> > > > More magic links to beam you around sounds like a bad idea. We had a
> > > > bunch of CVEs around them in containers and they were one of the major
> > > > reasons behind us pushing for openat2(). That's why it has a
> > > > RESOLVE_NO_MAGICLINKS flag.
> > >
> > > No, that link wouldn't beam you around at all, it would end up in an
> > > internally mounted instance of a mountfs, a safe place where no
> >
> > Even if it is a magic link to a safe place it's a magic link. They
> > aren't a great solution to this problem. fsinfo() is cleaner and
> > simpler as it creates a context for a supervised mount which gives the a
> > managing application fine-grained control and makes it easily
> > extendable.
>
> Yeah, it's a nice and clean interface in the ioctl(2) sense. Sure,
> fsinfo() is way better than ioctl(), but it at the core it's still the
> same syscall multiplexer, do everything hack.
In contrast to a generic ioctl() it's a domain-specific separate
syscall. You can't suddenly set kvm options through fsinfo() I would
hope. I find it at least debatable that a new filesystem is preferable.
And - feel free to simply dismiss the concerns I expressed - so far
there has not been a lot of excitement about this idea.
>
> > Also, we're apparently at the point where it seems were suggesting
> > another (pseudo)filesystem to get information about filesystems.
>
> Implementation detail. Why would you care?
I wouldn't call this an implementation detail. That's quite a big
design choice; it's a separate fileystem. In addition, implementation
details need to be maintained.
Christian
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