Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755090Ab3EPGT1 (ORCPT ); Thu, 16 May 2013 02:19:27 -0400 Received: from mail-ia0-f172.google.com ([209.85.210.172]:54873 "EHLO mail-ia0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752738Ab3EPGTW (ORCPT ); Thu, 16 May 2013 02:19:22 -0400 MIME-Version: 1.0 In-Reply-To: <20130514105119.66a5bc3f@corrin.poochiereds.net> References: <20130510102754.184cd90d@corrin.poochiereds.net> <20130514105119.66a5bc3f@corrin.poochiereds.net> Date: Thu, 16 May 2013 10:19:22 +0400 Message-ID: Subject: Re: Mount failure due to restricted access to a point along the mount path From: Pavel Shilovsky To: Jeff Layton Cc: Miklos Szeredi , linux-cifs , Steve French , Kernel Mailing List , sjayaraman@novell.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3169 Lines: 81 2013/5/14 Jeff Layton : > On Fri, 10 May 2013 10:27:54 -0400 > Jeff Layton wrote: > >> On Fri, 10 May 2013 16:13:30 +0200 >> Miklos Szeredi wrote: >> >> > Hi, >> > >> > A while ago this was discussed: >> > >> > http://thread.gmane.org/gmane.linux.kernel.cifs/7779 >> > >> > This is essentially a regression introduced by the shared superblock >> > changes in 3.0 and several SUSE customers are complaining about it. >> > I've created a temporary fix which reverts 29 commits related to the >> > shared superblock changes. It works, but it's obviously not a >> > permanent fix, especially since we definitely don't want to diverge >> > from mainline. >> > >> > Is this issue being worked on? Don't other distros have similar reports? >> > >> > Thanks, >> > Miklos >> >> I don't know of anyone currently working on it. There are a couple of >> possible approaches to fixing it, I think: >> >> 1) if the dentries to get down to the root of the mount don't already >> exist, then attach some sort of "placeholder" inode that can be fleshed >> out later if and when the dentry is accessed via other means. >> >> 2) do something like what NFS does (see commit 54ceac45). This becomes >> a bit more complicated due to the fact that the server may not hand out >> real inode numbers and we sometimes have to fake them up. >> >> #1 is probably simpler to implement, but I'll confess that I haven't >> thought through all of the potential problems with it. >> > > So, giving this some more thought, I think #2 is really the correct way > to fix this. Here's the main problem though: > > Suppose someone mounts: > > //server/share/foo/bar/baz > > We make the sb->s_root point to the top level share, and then create a > disconnected dentry for "baz" to return from ->mount. > > Then, a little while later, //server/share gets mounted separately and > a user walks down to /foo/bar/baz within the same share. > > How do we ensure that we don't end up with two "baz" dentries in this > situation? With NFS, we can be reasonably sure that there's a 1:1 > correspondance of filehandle to inode. > > Under CIFS, it's possible that it's faking up inode numbers if the > server doesn't provide them via a UniqueID field. The only real > identifying info we have for the inode in that case is the pathname. > > Perhaps we'd be best off to just rip out the sb sharing after all. > Getting all of the corner cases right when the protocol and server > implementations are so problematic is really, really difficult. > > If we do go that route, then the fscache code will need some work since > it uses the sharename as a sb cookie. Another option is to add mount options shared and nonshared (default) like NFS already has and let users use sharing capability if the permissions on server allow walking through a share path to a mount root. -- Best regards, Pavel Shilovsky. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/