Subject: Re: [RFC/PATCH] revoke/frevoke system calls V2
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: David Wagner <daw-usenet@taverner.cs.berkeley.edu>
Cc: linux-kernel@vger.kernel.org
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Date: Tue, 08 Aug 2006 13:13:20 +0100
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Ar Llu, 2006-08-07 am 22:52 +0000, ysgrifennodd David Wagner:
> I'm still trying to understand the semantics of this proposed
> frevoke() implementation.  Can an attacker use this to forcibly
> close some other processes' file descriptor?  Suppose the target

No.

> process has fd 0 open and the attacker revokes the file corresponding
> to fd 0; what is the state of fd 0 in the target process?  Is it
> closed?  If the target process then open()s another file, does it

No its revoked. Just like a tty hangup

> get bound to fd 0?  (Recall that open() always binds to the lowest
> unused fd.)  If the answers are "yes", then the security consequences
> seem very scary.

Of course it doesn't. The BSD folk who added revoke were security people
not idiots.

Alan

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