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From: Andreas Gruenbacher <agruen@suse.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
	Tony Jones <tonyj@suse.de>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	chrisw@sous-sol.org, linux-security-module@vger.kernel.org,
	viro@zeniv.linux.org.uk
Subject: Re: [RFC 0/28] Patches to pass vfsmount to LSM inode security hooks
Date: Mon, 5 Feb 2007 19:20:35 -0800	[thread overview]
Message-ID: <200702051920.36057.agruen@suse.de> (raw)
In-Reply-To: <20070205190230.GA23104@infradead.org>

On Monday 05 February 2007 11:02, Christoph Hellwig wrote:
> On Mon, Feb 05, 2007 at 10:58:26AM -0800, Trond Myklebust wrote:
> > On Mon, 2007-02-05 at 18:44 +0000, Christoph Hellwig wrote:
> > > Just FYI:  Al was very opposed to the idea of passing the vfsmount to
> > > the vfs_ helpers, so you should discuss this with him.
> > >
> > > Looking at the actual patches I see you're lazy in a lot of places.
> > > Please make sure that when you introduce a vfsmount argument somewhere
> > > that it is _always_ passed and not just when it's conveniant.  Yes,
> > > that's more work, but then again if you're not consistant anyone
> > > half-serious will laught at a security model using this infrasturcture.
> >
> > nfsd in particular tends to be a bit lazy about passing around vfsmount
> > info. Forcing it to do so should not be hard since the vfsmount is
> > already cached in the "struct export" (which can be found using the
> > filehandle). It will take a bit of re-engineering in order to pass that
> > information around inside the nfsd code, though.
>
> I actually have a patch to fix that.  It's part of a bigger series
> that's not quite ready, but I hope to finish all of it this month.

It's actually not hard to "fix", and nfsd would look a little less weird. But 
what would this add, what do pathnames mean in the context of nfsd, and would 
nfsd actually become less weird?

On the wire, nfs transmits file handles, not filenames. The file handle 
usually contains the inode numbers of the file and the containing directory.

The code in fs/exportfs/expfs.c:find_exported_dentry() shows that fh_verify() 
should return a dentry that may be connected or not, depending on the export 
options and whether it's a file or directory. Together with the vfsmount from 
the svc_export, we could compute a pathname.

But there is no way to tell different hardlinks to the same inode in the same 
directory from each other (both the file and directory inode are the same), 
and depending on the export options, we may or may not be able to distinguish 
different hardlinks across directories.

If the nohide or crossmnt export options are used, we might run into similar 
aliasing issues with mounts (I'm not sure about this).

So we could compute pathnames, but they wouldn't be very meaningful. Instead 
of going that way, it seems more reasonable to not do pathname based access 
control for the kernel kernel nfsd at all. Passing NULL as the vfsmounts does 
that. With a properly configured nfsd, the areas that remote users could 
access would still be well confined.

The focus with this whole pathname based security stuff really is to be able 
to better confine local processes. The kernel nfsd is a kernel thread, and as 
such, confining it from a security point of view cannot really work, anyway.

> > Note also that it might be nice to enforce the vfsmount argument by
> > replacing the existing dentry parameters with a struct path instead of
> > adding an extra reference to the vfsmount to existing functions.
>
> That definitly sounds like a good idea, independent of whether we want
> to pass the vfsmount in more places or not.

Note that you can still pass a NULL vfsmount in a struct path.

Thanks,
Andreas

  reply	other threads:[~2007-02-06  3:21 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-05 18:22 Tony Jones
2007-02-05 18:22 ` [RFC 1/28] Pass struct vfsmount to the inode_create LSM hook Tony Jones
2007-02-05 18:22 ` [RFC 2/28] Remove redundant check from proc_setattr() Tony Jones
2007-02-05 19:16   ` Chris Wright
2007-02-05 18:22 ` [RFC 3/28] Pass struct file down to remove_suid and children Tony Jones
2007-02-05 18:22 ` [RFC 4/28] Add a vfsmount parameter to notify_change() Tony Jones
2007-02-05 18:23 ` [RFC 5/28] Pass struct vfsmount to the inode_setattr LSM hook Tony Jones
2007-02-05 18:23 ` [RFC 6/28] Add struct vfsmount parameter to vfs_mkdir() Tony Jones
2007-02-05 18:23 ` [RFC 7/28] Pass struct vfsmount to the inode_mkdir LSM hook Tony Jones
2007-02-05 18:23 ` [RFC 8/28] Add a struct vfsmount parameter to vfs_mknod() Tony Jones
2007-02-05 18:23 ` [RFC 9/28] Pass struct vfsmount to the inode_mknod LSM hook Tony Jones
2007-02-05 18:23 ` [RFC 10/28] Add a struct vfsmount parameter to vfs_symlink() Tony Jones
2007-02-05 18:23 ` [RFC 11/28] Pass struct vfsmount to the inode_symlink LSM hook Tony Jones
2007-02-05 18:24 ` [RFC 12/28] Pass struct vfsmount to the inode_readlink " Tony Jones
2007-02-05 18:24 ` [RFC 13/28] Add struct vfsmount parameters to vfs_link() Tony Jones
2007-02-05 18:24 ` [RFC 14/28] Pass struct vfsmount to the inode_link LSM hook Tony Jones
2007-02-05 18:24 ` [RFC 15/28] Add a struct vfsmount parameter to vfs_rmdir() Tony Jones
2007-02-05 18:24 ` [RFC 16/28] Pass struct vfsmount to the inode_rmdir LSM hook Tony Jones
2007-02-05 18:24 ` [RFC 17/28] Add a struct vfsmount parameter to vfs_unlink() Tony Jones
2007-02-05 18:25 ` [RFC 18/28] Pass struct vfsmount to the inode_unlink LSM hook Tony Jones
2007-02-05 18:25 ` [RFC 19/28] Add struct vfsmount parameters to vfs_rename() Tony Jones
2007-02-05 18:25 ` [RFC 20/28] Pass struct vfsmount to the inode_rename LSM hook Tony Jones
2007-02-05 18:25 ` [RFC 21/28] Add a struct vfsmount parameter to vfs_setxattr() Tony Jones
2007-02-05 18:25 ` [RFC 22/28] Pass struct vfsmount to the inode_setxattr LSM hook Tony Jones
2007-02-05 18:25 ` [RFC 23/28] Add a struct vfsmount parameter to vfs_getxattr() Tony Jones
2007-02-05 18:25 ` [RFC 24/28] Pass struct vfsmount to the inode_getxattr LSM hook Tony Jones
2007-02-05 18:26 ` [RFC 25/28] Add a struct vfsmount parameter to vfs_listxattr() Tony Jones
2007-02-05 18:26 ` [RFC 26/28] Pass struct vfsmount to the inode_listxattr LSM hook Tony Jones
2007-02-05 18:26 ` [RFC 27/28] Add a struct vfsmount parameter to vfs_removexattr() Tony Jones
2007-02-05 18:26 ` [RFC 28/28] Pass struct vfsmount to the inode_removexattr LSM hook Tony Jones
2007-02-05 18:44 ` [RFC 0/28] Patches to pass vfsmount to LSM inode security hooks Christoph Hellwig
2007-02-05 18:58   ` Trond Myklebust
2007-02-05 19:02     ` Christoph Hellwig
2007-02-06  3:20       ` Andreas Gruenbacher [this message]
2007-02-06  8:51         ` Trond Myklebust
2007-02-06  9:48           ` Christoph Hellwig
2007-02-06 10:31             ` Neil Brown
2007-02-07  9:25           ` Andreas Gruenbacher
2007-02-06  9:47         ` Christoph Hellwig
2007-02-06 10:26           ` Neil Brown
2007-02-06 10:37             ` Christoph Hellwig
2007-02-12 18:32               ` J. Bruce Fields
2007-02-07  9:58           ` Andreas Gruenbacher
2007-02-07 12:11             ` Christoph Hellwig
2007-02-05 19:15     ` Chris Wright
2007-02-06  0:44   ` Andreas Gruenbacher
2007-02-06  2:13   ` Andreas Gruenbacher
2007-02-06  9:52     ` Christoph Hellwig
2007-02-07  9:04       ` Andreas Gruenbacher
2007-02-06 12:55     ` Stephen Smalley
2007-02-07  8:55       ` Andreas Gruenbacher
2007-02-07 15:43         ` Chris Wright
2007-02-07 16:06           ` Stephen Smalley
2007-02-07 16:25           ` Jeff Mahoney
2007-02-07 19:55             ` Andreas Gruenbacher
2007-02-05 19:26 ` Casey Schaufler
2007-02-05 19:39   ` Arjan van de Ven
2007-02-05 19:50   ` Chris Wright
2007-02-05 20:23     ` Casey Schaufler
2007-02-06  2:30     ` Andreas Gruenbacher
2007-02-06 14:20     ` Tetsuo Handa

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