Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poison overwritten
From: Pekka Enberg
Date: Mon Jul 21 2008 - 05:52:59 EST
Hi Ingo,
On Mon, Jul 21, 2008 at 12:41 PM, Ingo Molnar <mingo@xxxxxxx> 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 kkkkkkkkkkkkkkkï
Rest of the object looks correct.
> Redzone 0xf7ccc1b0: bb bb bb bb ïïïï
> 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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