linux-kernel - Re: [RFC] Privilege escalation in filesystems

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Message-ID: <20060809223755.GD1882@filer.fsl.cs.sunysb.edu>
Date:	Wed, 9 Aug 2006 18:37:55 -0400
From:	Josef Sipek <jsipek@....cs.sunysb.edu>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@....linux.org.uk>, ezk@...sunysb.edu,
	dquigley@...sunysb.edu, dpquigl@...ho.nsa.gov
Subject: Re: [RFC] Privilege escalation in filesystems

On Wed, Aug 09, 2006 at 06:17:32PM -0400, Trond Myklebust wrote:
> On Wed, 2006-08-09 at 17:52 -0400, Josef Sipek wrote:
...
> > (fs/nfs/nfs4recover.c:nfs4_save_user)
> > current->fsuid = 0;
> > current->fsgid = 0;
> 
> This sort of thing can be defeated by selinux.

I was affraid of that.

> The right way to perform privileged operations is normally to give the
> task to a kernel thread that has the required privileges (for instance a
> work_queue like keventd).

This makes sense. So, I suppose it would make sense to have a per-mount or
per-superblock pdflush-like thread that gets instantiated on mount.

> Ugh. Having the kernel interpret magic directory entries is just evil.
> Having the kernel magically create and remove said entries on behalf of
> the user ought to be punishable by death.

I'd like to hear about anything that is as portable, but not as "evil" :)

> Why can't you use something like an xattr to label opaqueness (or
> visibility!) instead?

The goal is to have as few restrictions as possible - not every file system
supports xattr.

Josef "Jeff" Sipek.

-- 
Bus Error: passangers dumped.
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