linux-kernel - Re: [bug, netconsole, SLUB] BUG skbuff_head

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Message-ID: <84144f020807210252k68d5cf65i8c7ae3c11cecc046@mail.gmail.com>
Date:	Mon, 21 Jul 2008 12:52:45 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"Vegard Nossum" <vegard.nossum@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, cl@...ux-foundation.org,
	davem@...emloft.net, johnpol@....mipt.ru
Subject: Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poison overwritten

Hi Ingo,

On Mon, Jul 21, 2008 at 12:41 PM, Ingo Molnar <mingo@...e.hu> wrote:
> update about this problem: just triggered another colorful crash, see
> below. This was with the 4K object dump patch already, maybe the dump
> gives a clue?

...to point out the obvious:

> =============================================================================
> BUG skbuff_head_cache: Poison overwritten
> -----------------------------------------------------------------------------
>
> INFO: 0xf7ccc100-0xf7ccc103. First byte 0x0 instead of 0x6b
> INFO: Allocated in __alloc_skb+0x30/0x10e age=1 cpu=1 pid=1
> INFO: Freed in __kfree_skb+0x63/0x66 age=1 cpu=0 pid=0
> INFO: Slab 0xc1c34ca0 objects=16 used=1 fp=0xf7ccc100 flags=0x400000c3
> INFO: Object 0xf7ccc100 @offset=256 fp=0xf7ccc200
>
> Bytes b4 0xf7ccc0f0:  5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
>  Object 0xf7ccc100:  00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b ....kkkkkkkkkkkk

Use after free where first four bytes are zeroed.

>  Object 0xf7ccc110:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc120:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc130:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc140:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc150:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc160:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc170:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc180:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc190:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xf7ccc1a0:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk�

Rest of the object looks correct.

>  Redzone 0xf7ccc1b0:  bb bb bb bb                                     ����
>  Padding 0xf7ccc1d8:  5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
>  Padding 0xf7ccc1e8:  5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
>  Padding 0xf7ccc1f8:  5a 5a 5a 5a 5a 5a 5a 5a                         ZZZZZZZZ
> Pid: 1, comm: swapper Not tainted 2.6.26-tip #3261
>  [<c01673ad>] print_trailer+0xd1/0xd9
>  [<c0167428>] check_bytes_and_report+0x73/0x8f
>  [<c0167664>] check_object+0xa5/0x15a
>  [<c016824c>] __slab_alloc+0x2fb/0x3c8
>  [<c0168364>] kmem_cache_alloc+0x4b/0xa8
>  [<c0497376>] ? __alloc_skb+0x30/0x10e
>  [<c0497376>] ? __alloc_skb+0x30/0x10e
>  [<c0497376>] __alloc_skb+0x30/0x10e
>  [<c04a6678>] alloc_skb+0xc/0xe
>  [<c04a6ce5>] find_skb+0x28/0x66
>  [<c04a6f5f>] netpoll_send_udp+0x2b/0x1cf
>  [<c058800f>] ? _spin_lock_irqsave+0x4b/0x55
>  [<c03db399>] write_msg+0x79/0xac
>  [<c03db320>] ? write_msg+0x0/0xac
>  [<c0122f96>] __call_console_drivers+0x56/0x63
>  [<c0122ffa>] _call_console_drivers+0x57/0x5b
>  [<c0123386>] release_console_sem+0x112/0x1a5
>  [<c01238f3>] vprintk+0x344/0x35e
> --
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