Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux2.6.34-rc3)

From: Linus Torvalds
Date: Tue Apr 06 2010 - 19:42:25 EST

On Wed, 7 Apr 2010, Borislav Petkov wrote:
> +
> + if (!anon_vma-> {
> + printk(KERN_ERR "NULL anon_vma->, 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 ('' 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.

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