DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:date:message-id:subject:from:to
         :cc:content-type:content-transfer-encoding;
        b=Hs9ZRE1rFQhcIsR9aFKox7gq5xsK99kyADA80pTI3tOlv4abI8hvibB1DZygt/aBAv
         fNDDyQDd8Ul89035swkxFwK8WxyTxpRcl7i3XbbOeZiicCEhqgtqMYf6eCy293EoJn6M
         nEGIIRpHRrzGHOUGQgG87znQ7W1wvvqs+7NOc=
MIME-Version: 1.0
In-Reply-To: <1244408607.9064.8.camel@Maple>
References: <19f34abd0905301323k1498ca3fv31b271de65d60afc@mail.gmail.com>
	 <1244408607.9064.8.camel@Maple>
Date: Mon, 8 Jun 2009 12:00:47 +0200
Message-ID: <19f34abd0906080300w796c6b65o6b537064cac917b0@mail.gmail.com>
Subject: Re: net: uninitialized loopback addr leaks to userspace
From: Vegard Nossum <vegard.nossum@gmail.com>
To: John Dykstra <john.dykstra1@gmail.com>
Cc: Linux Netdev List <netdev@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1896
Lines: 53

2009/6/7 John Dykstra <john.dykstra1@gmail.com>:
> On Sat, 2009-05-30 at 22:23 +0200, Vegard Nossum wrote:
>> It seems that loopback's hardware address is never initialized by the
>> kernel. So if userspace attempts to read this address before it has
>> been set, the kernel will return some uninitialized data (only 6
>> bytes, though).
>
> Thank you for the report, Vegard.
>
> I've been unable to reproduce the problem you describe, using
> 2.6-30-rc8, this test program and a couple of kernel builds for system
> load:
[...]
> ------------------------------------------------------------------
>
> Looking at the kernel code, it appears that all bytes of struct
> net_device, including the L2 address, are initialized to zeros at
> interface creation time.
>
> Can you spot a difference between your test procedures and mine that
> would enable me to reproduce the problem?

Hi,

I just tried your test program on a linux-next kernel, it works beautifully :-)

(I made one change: The stack grows downwards on x86, so I think you
should put child_stack + 16386 as the stack to clone()?)

As I wrote in reply to Stephen Hemminger, this problem seems to be
caused by a particular patch in linux-next:

commit f001fde5eadd915f4858d22ed70d7040f48767cf
Author: Jiri Pirko <jpirko@redhat.com>
Date:   Tue May 5 02:48:28 2009 +0000

   net: introduce a list of device addresses dev_addr_list (v6)

Thanks for testing.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/