linux-kernel - Re: [RFC 2/2] fanotify: emit FAN_MODIFY

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Date:   Tue, 21 Mar 2017 17:41:22 +0100
From:   Jan Kara <jack@...e.cz>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        Filip Štědronský <r.lklm@...narg.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Marko Rauhamaa <marko.rauhamaa@...ecure.com>
Subject: Re: [RFC 2/2] fanotify: emit FAN_MODIFY_DIR on filesystem changes

On Tue 21-03-17 11:38:49, J. Bruce Fields wrote:
> On Sun, Mar 19, 2017 at 11:19:43AM +0100, Jan Kara wrote:
> > On Tue 14-03-17 13:18:01, Amir Goldstein wrote:
> > > On Tue, Mar 14, 2017 at 1:03 AM, Filip Štědronský <r.lklm@...narg.cz> wrote:
> > > > Besause fanotify requires `struct path`, the event cannot be generated
> > > > directly in `fsnotify_move` and friends because they only get the inode
> > > > (and their callers, `vfs_rename`&co. cannot supply any better info).
> > > > So instead it needs to be generated higher in the call chain, i.e. in
> > > > the callers of functions like `vfs_rename`.
> > > >
> > > > This leads to some code duplication. Currently, there are several places
> > > > whence functions like `vfs_rename` or `vfs_unlink` are called:
> > > >
> > > >   * syscall handlers (done)
> > > >   * NFS server (done)
> > > >   * stacked filesystems
> > > >       - ecryptfs (done)
> > > >       - overlayfs
> > > >         (Currently doesn't report even ordinary fanotify events, because
> > > >          it internally clones the upper mount; not sure about the
> > > >          rationale.  One can always watch the overlay mount instead.)
> > > >   * few rather minor things
> > > >       - devtmpfs
> > > >         (its internal changes are not tied to any vfsmount so it cannot
> > > >          emit mount-scoped events)
> > > >       - cachefiles (done)
> > > >       - ipc/mqueue.c (done)
> > > >       - fs/nfsd/nfs4recover.c (done)
> > > >       - kernel/bpf/inode.c (done)
> > > >         net/unix/af_unix.c (done)
> > > >
> > > > (grep -rE '\bvfs_(rename|unlink|mknod|whiteout|create|mkdir|rmdir|symlink|link)\(')
> > > >
> > > > Signed-off-by: Filip Štědronský <r.lkml@...narg.cz>
> > > >
> > > > ---
> > > >
> > > > An alternative might be to create wrapper functions like
> > > > vfs_path_(rename|unlink|...). They could also take care of calling
> > > > security_path_(rename|unlink|...), which is currently also up to
> > > > the indvidual callers (possibly with a flag because it might not
> > > > be always desired).
> > > 
> > > That's an interesting idea. There is some duplicity between security/audit
> > > hook and fsnotify hooks. It should be interesting to try and deduplicate
> > > some of this code.
> > 
> > Yeah, but ecryptfs or nfsd don't actually call these security hooks AFAICT.
> 
> We don't?  E.g. nfsd_unlink calls vfs_unlink which calls
> security_inode_unlink().

OK, I have not been specific enough :). ecryptfs or nfsd don't call *path*
security hooks AFAICT - e.g. security_path_unlink() from nfsd_unlink().

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR