linux-kernel - Re: [patch 7/8] fdmap v2

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Message-ID: <20070609165454.GE4095@ftp.linux.org.uk>
Date:	Sat, 9 Jun 2007 17:54:54 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>,
	Eric Dumazet <dada1@...mosbay.com>,
	Kyle Moffett <mrmacman_g4@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

On Sat, Jun 09, 2007 at 09:26:34AM -0700, Ulrich Drepper wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Al Viro wrote:
> > So which code is supposed to do that open/write in your example?  Library?
> > Unmodified application?  Application specifically modified to make *that*
> > open() randomized?
> 
> Why should that matter?  All of the above.

I asked for real-world example.  Can I have one, please?

> In whatever way you look at it, there currently is a problem which
> cannot be solved except with truly horrible, horrible hack (open N
> descriptors and randomly select one to use; yep, horrible, I said so).

That's simply not true.  On the current kernel nothing stops you from e.g.
picking a random number and using F_DUPFD.  Voila - there's your randomized
descriptor.  Portable to earlier kernels.

Moreover, nonsense^H^H^Hq_fd() can be implemented in userland just fine
if we allow F_DUPFD to arbitrary number - just pass it a random one *or*
base chosen like davedel is doing (constant + 20bit random chosen at start
time).
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