Messages in this thread | | | Subject | Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3) | From | Peter Zijlstra <> | Date | Wed, 07 Apr 2010 10:36:43 +0200 |
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On Tue, 2010-04-06 at 11:28 -0700, Linus Torvalds wrote: > Just as an example of the kind of code that makes me worry: > > void unlink_anon_vmas(struct vm_area_struct *vma) > { > struct anon_vma_chain *avc, *next; > > /* Unlink each anon_vma chained to the VMA. */ > list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) { > anon_vma_unlink(avc); > list_del(&avc->same_vma); > anon_vma_chain_free(avc); > } > } > > Now, think about what happens for the *last* entry in that avc chain. It > will call that "anon_vma_unlink()" thing, which will delete perhaps the > last entry in the "same_anon_vma" one, and then it does > > if (empty) > anon_vma_free(anon_vma); > > *before* unlink_anon_vma's has actually does that > > list_del(&avc->same_vma); > > and what we essentially have is a stale anon_vma_chain entry that still > exists on that same_vma list, and points to an anon_vma that already got > deleted. > > Does it matter? I really can't see that it does.
I think it does, the anon_vma thing has an RCU destroyed slab, but that doesn't mean the anon_vma object itself is rcu delayed. The moment we free it it can be re-used. So the above use after free is a bug.
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