Subject: Re: [Bugme-new] [Bug 27212] New: Warning kmemcheck: Caught 64-bit read from uninitialized memory in netlink_broadcast_filtered

From: Pekka Enberg <[email-masked]>
Date: Fri, 21 Jan 2011 09:49:45 +0200

On 1/20/11 10:41 PM, Eric Dumazet wrote:
> Le jeudi 20 janvier 2011 à 12:25 -0800, Andrew Morton a écrit :
>> (switched to email.  Please respond via emailed reply-to-all, not via the
>> bugzilla web interface).
>>
>> On Thu, 20 Jan 2011 20:08:32 GMT
>> [email-masked] wrote:
>>
>>> https://bugzilla.kernel.org/show_bug.cgi?id=27212
>>>
>>>             Summary: Warning kmemcheck: Caught 64-bit read from
>>>                      uninitialized memory in netlink_broadcast_filtered
>>>             Product: Other
>>>             Version: 2.5
>>>      Kernel Version: 2.6.38-rc1
>>>            Platform: All
>>>          OS/Version: Linux
>>>                Tree: Mainline
>>>              Status: NEW
>>>            Severity: normal
>>>            Priority: P1
>>>           Component: Other
>>>          AssignedTo: [email-masked]
>>>          ReportedBy: [email-masked]
>>>          Regression: Yes
>>>
>>>
>>> Athlon 64 X2 3000 in 64bits
>>> Slackware64 13.1
>>> Kernel compiled with kmemcheck and other debug options
>>>
>>> At boot I got the following warning:
>>>
>>> PCI: Using ACPI for IRQ routing
>>> PCI: pci_cache_line_size set to 64 bytes
>>> pci 0000:00:00.0: address space collision: [mem 0xe0000000-0xefffffff pref]
>>> conflicts with GART [mem 0x
>>> e0000000-0xefffffff]
>>> reserve RAM buffer: 000000000009fc00 - 000000000009ffff
>>> reserve RAM buffer: 000000003ffb0000 - 000000003fffffff
>>> WARNING: kmemcheck: Caught 64-bit read from uninitialized memory
>>> (ffff88003e170eb0)
>>> 0000000000000000010000000000000000000000000000000000000000000000
>>>   i i i i i i i i i i i i u u u u u u u u u u u u u u u u u u u u
>>>                                   ^
>>>
>>> Pid: 1, comm: swapper Not tainted 2.6.38-rc1 #2 K8 Combo-Z/K8 Combo-Z
>>> RIP: 0010:[<ffffffff8127ad72>]  [<ffffffff8127ad72>] memmove+0x122/0x1a0
>>> RSP: 0018:ffff88003e0b3c60  EFLAGS: 00010202
>>> RAX: ffff88003e170080 RBX: ffff88003e27b500 RCX: 0000000000000020
>>> RDX: 0000000000000018 RSI: ffff88003e170ea0 RDI: ffff88003e1700a0
>>> RBP: ffff88003e0b3c60 R08: 0000000000000001 R09: 0000000000000001
>>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>>> R13: 0000000000000080 R14: 0000000000000000 R15: 0000000000000001
>>> FS:  0000000000000000(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>> CR2: ffff88003e018abc CR3: 0000000001a1c000 CR4: 00000000000006f0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
>>>   [<ffffffff814741c2>] pskb_expand_head+0xc2/0x2a0
>>>   [<ffffffff81498fa7>] netlink_broadcast_filtered+0xa7/0x4a0
>>>   [<ffffffff814993b8>] netlink_broadcast+0x18/0x20
>>>   [<ffffffff8149b884>] genlmsg_mcast+0x144/0x180
>>>   [<ffffffff8149bc4a>] genl_ctrl_event+0xca/0x450
>>>   [<ffffffff8149c75d>] genl_register_mc_group+0x10d/0x2a0
>>>   [<ffffffff81ad9da4>] genl_init+0x6c/0x84
>>>   [<ffffffff810001de>] do_one_initcall+0x3e/0x170
>>>   [<ffffffff81aae6ea>] kernel_init+0x197/0x21b
>>>   [<ffffffff81003254>] kernel_thread_helper+0x4/0x10
>>>   [<ffffffffffffffff>] 0xffffffffffffffff
>>> pnp: PnP ACPI init
>>> ACPI: bus type pnp registered
>>> pnp 00:00: [bus 00-ff]
>>> pnp 00:00: [io  0x0cf8-0x0cff]
>>>
>>> This is specific to 2.6.38-rc1.
>>>
> Likely a false positive after commit ca44ac38
> (net: don't reallocate skb->head unless the current one hasn't the
> needed extra size or is shared)
>
> ksize() allows us to use a bit more than what was asked at kmalloc()
> time, because of discrete kmem caches sizes.
>
> We probably need to instruct kmemcheck of this.

It actually looks like a bug in SLUB+kmemcheck. The 
kmemcheck_slab_alloc() call in slab_post_alloc_hook() should use ksize() 
instead of s->objsize. SLAB seems to do the right thing already. Anyone 
care to send a patch my way?

             Pekka