linux-kernel - Re: [PATCH] fanotify: remove redundant capable(CAP_SYS

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Message-ID: <20190605102611.GA4546@poseidon.Home>
Date:   Wed, 5 Jun 2019 20:26:13 +1000
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Christian Brauner <christian@...uner.io>, Jan Kara <jack@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fanotify: remove redundant capable(CAP_SYS_ADMIN)s

On Thu, May 23, 2019 at 01:25:08PM +0300, Amir Goldstein wrote:

...

> > > > Interesting. When do you think the gate can be removed?
> > >
> > > Nobody is working on this AFAIK.
> > > What I posted was a simple POC, but I have no use case for this.
> > > In the patchwork link above, Jan has listed the prerequisites for
> > > removing the gate.
> > >
> > > One of the prerequisites is FAN_REPORT_FID, which is now merged.
> > > When events gets reported with fid instead of fd, unprivileged user
> > > (hopefully) cannot use fid for privilege escalation.
> > >
> > > > I was looking into switching from inotify to fanotify but since it's not usable from
> > > > non-initial userns it's a no-no
> > > > since we support nested workloads.
> > >
> > > One of Jan's questions was what is the benefit of using inotify-compatible
> > > fanotify vs. using inotify.
> > > So what was the reason you were looking into switching from inotify to fanotify?
> > > Is it because of mount/filesystem watch? Because making those available for
> >
> > Yeah. Well, I would need to look but you could probably do it safely for
> > filesystems mountable in user namespaces (which are few).
> > Can you do a bind-mount and then place a watch on the bind-mount or is
> > this superblock based?
> >
> 
> Either.
> FAN_MARK_MOUNT was there from day 1 of fanotify.
> FAN_MARK_FILESYSTEM was merged to Linux Linux 4.20.
> 
> But directory modification events that are supported since v5.1 are
> not available
> with FAN_MARK_MOUNT, see:
> https://github.com/amir73il/man-pages/blob/fanotify_fid/man2/fanotify_init.2#L97
> 
> Matthew,
> 
> Perhaps this fact is worth a mention in the linked entry for FAN_REPORT_FID
> in fanotify_init.2 in addition to the comment on the entry for FAN_MARK_MOUNT
> in fanotify_mark.2.

Sorry, a little late to the party...

The fact being that directory modification events that are supported since v5.1
are not available when used in conjunction with FAN_MARK_MOUNT?

-- 
Matthew Bobrowski