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Subject: Re: slab corruption with current -git
From: David Miller <davem@davemloft.net>
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From: David Miller <davem@davemloft.net>
Date: Sun, 09 Oct 2016 23:57:45 -0400 (EDT)

> From: Linus Torvalds <torvalds@linux-foundation.org>
> Date: Sun, 9 Oct 2016 20:41:17 -0700
> 
>> Note that the "correct way" of doing list operations also almost
>> inevitably is the shortest way by far, since it gets rid of all the
>> special cases. So the patch looks nice. It gets rid of the magic
>> "nf_set_hooks_head()" thing too, because once you do list following
>> right, the head is no different from any other pointer in the list.
> 
> Perhaps we should have some "slist" primitives added to
> include/linux/list.h but since the comparison differs for each user I
> guess it's hard to abstract in a way that's generic and inlines
> properly.
> 
> I'll start taking a look at your patch and this stuff as well, thanks
> Linus.

So I've been reviewing this patch and it looks fine, but I also want
to figure out what is actually causing the OOPS and I can't spot it
yet.

One possible way to see that oops is to free the head entry of the
chain without unlinking it.  The next unregister will dereference a
POISON pointer.

Actually...

The POISON value comes not from a hook entry, but from the array of
pointers in the per-netns datastructure.

This means that the netns is possibly getting freed up before we
unregister the netfilter hooks.