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From: Miklos Szeredi <miklos@szeredi.hu>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: fsnotify events for overlayfs real file
Date: Mon, 31 May 2021 17:18:48 +0200	[thread overview]
Message-ID: <CAJfpegsqqwMgtDKESNVXvtYU=fsu2pZ_nE8UdXQSLudKqK8Xmw@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxhsxmzWp+YMRBA3xFDzJ1ov--n=f+VAnBsJZ_4DyHoYXw@mail.gmail.com>

On Tue, 18 May 2021 at 19:56, Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Tue, May 18, 2021 at 5:43 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Mon, 10 May 2021 at 18:32, Amir Goldstein <amir73il@gmail.com> wrote:

> > > My thinking was that we can change d_real() to provide the real path:
> > >
> > > static inline struct path d_real_path(struct path *path,
> > >                                     const struct inode *inode)
> > > {
> > >         struct realpath = {};
> > >         if (!unlikely(dentry->d_flags & DCACHE_OP_REAL))
> > >                return *path;
> > >         dentry->d_op->d_real(path->dentry, inode, &realpath);
> > >         return realpath;
> > > }

Real paths are internal, we can't pass them (as fd in permission
events) to userspace.

> > >
> > >
> > > Another option, instead of getting the realpath, just detect the
> > > mismatch of file_inode(file) != d_inode(path->dentry) in
> > > fanotify_file() and pass FSNOTIFY_EVENT_DENTRY data type
> > > with d_real() dentry to backend instead of FSNOTIFY_EVENT_PATH.
> > >
> > > For inotify it should be enough and for fanotify it is enough for
> > > FAN_REPORT_FID and legacy fanotify can report FAN_NOFD,
> > > so at least permission events listeners can identify the situation and
> > > be able to block access to unknown paths.

That sounds like a good short term solution.


>
> Is there a reason for the fake path besides the displayed path in
> /proc/self/maps?

I'm not aware of any.

>
> Does it make sense to keep one realfile with fake path for mmaped
> files along side a realfile with private/detached path used for all the
> other operations?

This should work, but it would add more open files, so needs some good
justifications.

> While at it, we can also cache both upper and lower realfiles in case
> file was copied up after open.

Right, although this doesn't seem to be an issue (it's a rare corner
case that is being cared for).

Thanks,
Miklos

  reply	other threads:[~2021-05-31 17:08 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 16:31 fsnotify events for overlayfs real file Amir Goldstein
2021-05-18 14:43 ` Miklos Szeredi
2021-05-18 17:56   ` Amir Goldstein
2021-05-31 15:18     ` Miklos Szeredi [this message]
2021-05-31 18:26       ` Amir Goldstein
2021-06-01  9:08         ` Christian Brauner
2021-06-08 12:05         ` Marko Rauhamaa

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