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Date: Tue, 6 Aug 2002 10:10:59 +0200
From: "Udo A. Steinberg" <us15@os.inf.tu-dresden.de>
To: Jeff Dike <jdike@karaya.com>
Cc: rz@linux-m68k.org, alan@redhat.com, mingo@elte.hu,
       linux-kernel@vger.kernel.org
Subject: Re: context switch vs. signal delivery [was: Re: Accelerating user mode
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	<200208060255.VAA04809@ccure.karaya.com>
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On Mon, 05 Aug 2002 21:55:05 -0500
> 
> > If you have one process per task and a kernel process, the kernel
> > process cannot change socket ownership over to the next task's
> > process, because it's not allowed to.
> 
> Why not?  I see nothing at all in the implementation of F_SETOWN that requires
> that it be called by the current owner:
> 
> 		case F_SETOWN:
> 			lock_kernel();
> 			filp->f_owner.pid = arg;
> 			filp->f_owner.uid = current->uid;
> 			filp->f_owner.euid = current->euid;
> 			...

Ok, I was looking at sockets and not tty's and that has the following in
net/core/sock.c
                   case F_SETOWN:
                        /*
                         * This is a little restrictive, but it's the only
                         * way to make sure that you can't send a sigurg to
                         * another process.
                         */
                        if (current->pgrp != -arg &&
                                current->pid != arg &&
                                !capable(CAP_KILL)) return(-EPERM);
                        sk->proc = arg;
                        return(0);

So it wouldn't work with socketpairs, but with tty's it should.

-Udo.
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