Re: [RFC/PATCH] revoke/frevoke system calls V2

From: Chase Venters
Date: Mon Aug 07 2006 - 19:10:59 EST

On Monday 07 August 2006 17:56, Daniel Jacobowitz wrote:
> On Mon, Aug 07, 2006 at 10:52:59PM +0000, David Wagner wrote:
> > 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
> > 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
> > 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.
> No, that's already been answered at least once. The file remains open,
> but returns EBADF on various operations.

IIRC, it returns EBADF because the file actually gets closed. The file
descriptor, on the other hand, is permanently leaked.

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