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

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Message-Id: <20060809200019.0bd5eecd.froese@gmx.de>
Date:	Wed, 9 Aug 2006 20:00:19 +0200
From:	Edgar Toernig <froese@....de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, Pavel Machek <pavel@....cz>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...l.org, viro@...iv.linux.org.uk, tytso@....edu,
	tigran@...itas.com
Subject: Re: [RFC/PATCH] revoke/frevoke system calls V2

Alan Cox wrote:
>
> Ar Mer, 2006-08-09 am 10:41 +0200, ysgrifennodd Edgar Toernig:
> > > If I own the file I can make it a symlink to a pty/tty pair
> > > I can revoke a pty/tty pair
> > 
> > With the EIO/EOF behaviour that's not a problem - apps that deal
> > with ttys have to expect that condition.
> 
> Think about it a moment - I can symlink any file to a tty/pty pair so
> any file I own you open might be a tty.

Yes, OK.  The EIO/EOF behaviour is fine.  Even for regular files it's
not something extraordinary.

> > Hmm... which apps have an open fd on block devices?  Usually a
> 
> cdrecord, cd audio players, eject, ....

And killing them is not OK?  "fuser -km /dev/cdrom" already covers both
cases, mounted somewhere and opened for special access.

Sorry if I sound a little bit anal.  IMO, a generic revoke is a pretty
sharp sword which is given to ordinary users and I have a very uneasy
feeling.  They can dig in the innards of other people's processes - a
clean headshot by root is something different ...

Ciao, ET.
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