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

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Message-Id: <200607271930.k6RJUQ6s016546@laptop13.inf.utfsm.cl>
Date:	Thu, 27 Jul 2006 15:30:26 -0400
From:	"Horst H. von Brand" <vonbrand@....utfsm.cl>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Petr Baudis <pasky@...e.cz>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, akpm@...l.org,
	viro@...iv.linux.org.uk, alan@...rguk.ukuu.org.uk, tytso@....edu,
	tigran@...itas.com
Subject: Re: [RFC/PATCH] revoke/frevoke system calls V2 

Pekka Enberg <penberg@...helsinki.fi> wrote:
> On Thu, 2006-07-27 at 20:06 +0200, Petr Baudis wrote:
> > Make that setuid root or just create log file owned by you and make root
> > run it.  Should be innocent enough, right?
> > 
> > Well, except that you can revoke the log file before the shadow file is
> > opened, at which point open() probably reuses the fd and the program
> > conveniently logs to /etc/shadow.

> No, the fd is leaked on purpose to avoid recycling. See revoke_fds for
> details.

Doesn't that violate a POSIX guarantee that the lowest unused fd is
returned? If the leakage lasts "long enough", this gives an opportunity of
a nice DoS by using up fds...
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
Departamento de Informatica                     Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria              +56 32 654239
Casilla 110-V, Valparaiso, Chile                Fax:  +56 32 797513

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