Ingo Molnar a écrit :

* Eric Dumazet [off-list ref] wrote:

quoted

Eric Dumazet a écrit :

quoted

Vegard Nossum a écrit :

quoted

2009/6/7 John Dykstra [off-list ref]:

quoted

On Sat, 2009-05-30 at 22:23 +0200, Vegard Nossum wrote:

quoted

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:

[...]

quoted

------------------------------------------------------------------

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 [off-list ref]
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 <redacted>
Signed-off-by: Eric Dumazet <redacted>

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 <redacted>
Signed-off-by: Eric Dumazet <redacted>

Could you please put the word 'kmemcheck' somewhere into the 
changelog, to make git-grepping and historic comparisons easier?

Sure I can do that, giving me opportunity to use my current email address,
since dada1@cosmosbay.com will disappear shortly.

Thank you

[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.

With kmemcheck help, Vegard found some uninitialized memory
was read and reported to user, potentialy leaking kernel data.
( thread can be found on http://lkml.org/lkml/2009/5/30/177 )

dev_addr_init() incorrectly uses sizeof() operator. We were
initializing one byte instead of MAX_ADDR_LEN bytes.

Reported-by: Vegard Nossum <redacted>
Signed-off-by: Eric Dumazet <redacted>
Acked-by: Jiri Pirko <redacted>
---

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) {
 		/*