Re: [PATCH] private mounts

[Pavel Machek]

Hi!

> > > Is it possible to limit all these from kernelspace?  Probably yes,
> > > although a timeout for operations is something that cuts either way.
> > > And the compexity of these checks would probably be orders of
> > > magnitude higher then the check we are currently discussing.
> > 
> > Yes ... but does the check we are discussing really solve the
> > problem?
> > 
> > Let's say that you attempt to export home directories of users by a
> > user-space NFS daemon. This daemon probably changes its fsuid to
> > match the remote user, so the check happily accepts the access and
> > the user is able to lock up the daemon.
> 
> Valid point.  The only defense is that when a program set's fsuid,
> it's performing the operation "on behalf of the user".  So the user is
> actually doing DoS against himself.
> 
> Of course this is not strictly true.  E.g. in the userspace NFS case
> it's probably a DoS against all users of the mount.

Exactly. So can we simply merge root-only fuse, and then worry
how to make it safe with user-mounted fuse. See your own unfsd example
why user-mounting is bad.

One possible solution would be to have root-owned fused that
talks to user-owned fused-s and checks they are behaving correctly?

Second is somehow improving those two lines this long thread is all about...

				Pavel
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