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Date: Sat, 9 Apr 2016 07:08:30 -0700
From: lazytyped <lazytyped@...il.com>
To: kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v2] mm: SLAB freelist randomization



On 4/8/16 11:03 AM, Thomas Garnier wrote:
> For example this attack against SLUB (also applicable against SLAB)
> would be affected:
> https://jon.oberheide.org/blog/2010/09/10/linux-kernel-can-slub-overflow/

would it?

- allocate a ton of shmid_kernel until you get a fresh page
- free one of such objects (here is where your randomization comes into
play)
- allocate the "vulnerable" object
- trigger the overflow
- start "freeing" the others - one will work

This doesn't work only in the case in which you are the last object in
the SLUB. So what you are achieving is a 1/(pagesize/sizeof_objects)
chance of making the attack less reliable. But I can free yet another
object and retry, if the previous overflow didn't kill me (simplest way
to guarantee that is to not completely fill the newly allocated SLUB page).


       -   twiz

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