linux-kernel - Re: [PATCH v3] vfs: new O

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Message-Id: <E1NHeXH-0003Lb-3q@pomaz-ex.szeredi.hu>
Date:	Mon, 07 Dec 2009 15:25:59 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	miklos@...redi.hu, miklos@...redi.hu, luto@....edu,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] vfs: new O_NODE open flag

On Mon, 7 Dec 2009, Alan Cox wrote:
> > > That is *exactly* the problem, which is clearly what you are missing here.
> > 
> > I don't think so, but maybe I'm wrong.  Could you describe your attack
> > scenario in detail then, please?
> 
> First obvious attack: get an O_NODE handle to a device you have assigned
> to your ownership
> 
> 	while(1)
> 		fchmod(fd, 0666);
> 
> wait for device to unload, reload and be intended for another user
> Race udev to a real open. You have a similar problem with vhangup() and
> ttys.

If this was a udev device, the same attack is possible with a hard
link to the device.  Except the attacker simply does link() instad of
open(O_NODE) and chmod() instead of fchmod().

See?

Thanks,
Miklos
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