Re: [PATCH v3] vfs: new O_NODE open flag

[Miklos Szeredi]

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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