Re: [RFC] Privilege escalation in filesystems

From: Josef Sipek
Date: Wed Aug 09 2006 - 18:36:04 EST

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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