Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL pointer dereference

Dieter Ries
2008-07-25T08:02:29Z

Pekka Enberg schrieb:
> On Thu, 2008-07-24 at 11:51 -0700, Andrew Morton wrote:
>> On Thu, 24 Jul 2008 16:34:36 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote:
>>
>>>>>> Your patch introduced a use-after-free and double-free.
>>>>>> krealloc() frees the old pointer, but it is still used
>>>>>> for the ->move operations, then freed again.
>>>>>>
>>>>>> To fix this I think we need a __krealloc() that doesn't
>>>>>> free the old memory, especially since it must not be
>>>>>> freed immediately because it may still be used in a RCU
>>>>>> read side (see the last part in the patch attached to
>>>>>> this mail (based on a kernel without your patch)).
>>>>> Agreed. Something like this, perhaps?
>>>>>
>>>>> [PATCH] netfilter: fix double-free and use-after free
>>>>>
>>>>> As suggested by Patrick McHardy, introduce a __krealloc() that doesn't
>>>>> free the original buffer to fix a double-free and use-after-free bug
>>>>> introduced by me in netfilter that uses RCU.
>>>>>
>>>>> Reported-by: Patrick McHardy <kaber@trash.net>
>>>>> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
>>>> Looks good to me, thanks.
>>> Ingo, can you please test this? Andrew, I'm at OLS so can you pick up
>>> the patch in your tree?
>> Sure. Or Patrick can do so and it can be merged via the net tree.
>>
>> Ingo, did this patch actually fix something over there?
>
> Apparently it didn't but it did fix Dieter's problem:
>
> http://lkml.org/lkml/2008/7/24/337
>
> Dieter, can we add a Tested-by tag from you to this patch?
>

Yes, it definitely fixed my issue and I have not encountered
further problems with the patch. The machine
is running fine with it.

Do I have to explicitly add my
Tested-by: Dieter Ries <clip2@gmx.de>
tag somewhere (if yes, where?) or is this enough for you?

cu
Dieter