linux-kernel - Re: [PATCH net-next-2.6] net: dev_addr

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Date:	Mon, 8 Jun 2009 14:41:59 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Vegard Nossum <vegard.nossum@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	John Dykstra <john.dykstra1@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] net: dev_addr_init() fix

Mon, Jun 08, 2009 at 02:13:32PM CEST, dada1@...mosbay.com wrote:
>Eric Dumazet a écrit :
>> Vegard Nossum a écrit :
>>> 2009/6/7 John Dykstra <john.dykstra1@...il.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@...hat.com>
>>> Date:   Tue May 5 02:48:28 2009 +0000
>>>
>>>    net: introduce a list of device addresses dev_addr_list (v6)
>>>
>> 
>> I believe following patch should fix this problem.
>> 
>> Thank you
>> 
>> [PATCH net-next-2.6] net: loopback device dev->addr_len fix
>> 
>> commit f001fde5eadd915f4858d22ed70d7040f48767cf 
>> (net: introduce a list of device addresses dev_addr_list (v6))
>> added one regression Vegard Nossum found in its testings.
>> 
>> loopback device doesnt have a hw address, we should set its
>> dev->addr_len to 0, not ETH_ALEN.
>> 
>> Reported-by: Vegard Nossum <vegard.nossum@...il.com>
>> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

oops, sorry for this...

Signed-off-by: Jiri Pirko <jpirko@...hat.com>

>
>Oh well, following is probably even more appropriate
>
>[PATCH net-next-2.6] net: dev_addr_init() fix
>
>commit f001fde5eadd915f4858d22ed70d7040f48767cf 
>(net: introduce a list of device addresses dev_addr_list (v6))
>added one regression Vegard Nossum found in its testings.
>
>dev_addr_init() incorrectly uses sizeof() operator
>
>Reported-by: Vegard Nossum <vegard.nossum@...il.com>
>Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>---
>diff --git a/net/core/dev.c b/net/core/dev.c
>index 1f38401..65387d9 100644
>--- a/net/core/dev.c
>+++ b/net/core/dev.c
>@@ -3655,8 +3655,8 @@ static int dev_addr_init(struct net_device *dev)
> 	/* rtnl_mutex must be held here */
> 
> 	INIT_LIST_HEAD(&dev->dev_addr_list);
>-	memset(addr, 0, sizeof(*addr));
>-	err = __hw_addr_add(&dev->dev_addr_list, NULL, addr, sizeof(*addr),
>+	memset(addr, 0, sizeof(addr));
>+	err = __hw_addr_add(&dev->dev_addr_list, NULL, addr, sizeof(addr),
> 			    NETDEV_HW_ADDR_T_LAN);
> 	if (!err) {
> 		/*
>
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