linux-kernel - Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

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Message-ID: <alpine.LFD.2.00.1004061630410.3487@i5.linux-foundation.org>
Date:	Tue, 6 Apr 2010 16:37:51 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux
 2.6.34-rc3)

On Wed, 7 Apr 2010, Borislav Petkov wrote:
> +
> +	if (!anon_vma->head.next) {
> +		printk(KERN_ERR "NULL anon_vma->head.next, page %lu\n",
> +				page_to_pfn(page));
> +
> +		object_err(anon_vma_cachep, page, (u8 *)anon_vma, "NULL next");

Oh, and since the debugging code never triggered ('head.next' wasn't 
actually NULL), you never got here, but the 'page' you passed in to 
object_error() should be the page of the slab allocation, not the page 
associated with the anon_vma.

So it should be something like "virt_to_head_page(anon_vma)" that you pass 
in to object_err().

Not that it matters. I assume it is the fact that SLAB debugging is on 
that actually turns the NULL into a non-NULL thing. Poisoning is not 
active for SLUb's with constructors or RCU-freeing, but things like 
redzoning still are. So enabling SLUB debugging will change the offsets 
within the pages of all the SLUB allocations.  I wonder if that's just 
what caused it to now have that 0x002e2e2e002e2e2e instead of NULL.

		Linus
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