>From 86f4f1f6deb76849e00c761fa30eeb479f789c35 Mon Sep 17 00:00:00 2001 From: Alexander Popov <alex.po...@linux.com> Date: Mon, 24 Jul 2017 23:16:28 +0300 Subject: [PATCH 2/2] mm/slub.c: add a naive detection of double free or corruption
On 25.07.2017 00:17, Alexander Popov wrote: > On 06.07.2017 03:27, Kees Cook wrote: >> This SLUB free list pointer obfuscation code is modified from Brad >> Spengler/PaX Team's code in the last public patch of grsecurity/PaX based >> on my understanding of the code. Changes or omissions from the original >> code are mine and don't reflect the original grsecurity/PaX code. >> >> This adds a per-cache random value to SLUB caches that is XORed with >> their freelist pointer address and value. This adds nearly zero overhead >> and frustrates the very common heap overflow exploitation method of >> overwriting freelist pointers. A recent example of the attack is written >> up here: http://cyseclabs.com/blog/cve-2016-6187-heap-off-by-one-exploit >> >> This is based on patches by Daniel Micay, and refactored to minimize the >> use of #ifdef. > > Hello! > > This is an addition to the SLAB_FREELIST_HARDENED feature. I'm sending it > according the discussion here: > http://www.openwall.com/lists/kernel-hardening/2017/07/17/9 In my previous message my email client wrapped one line and corrupted the patch. Excuse me for that. See the fixed patch below. -- >8 -- Add an assertion similar to "fasttop" check in GNU C Library allocator as a part of SLAB_FREELIST_HARDENED feature. An object added to a singly linked freelist should not point to itself. That helps to detect some double free errors (e.g. CVE-2017-2636) without slub_debug and KASAN. Signed-off-by: Alexander Popov <alex.po...@linux.com> --- mm/slub.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index c92d636..f39d06e 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -290,6 +290,10 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) { unsigned long freeptr_addr = (unsigned long)object + s->offset; +#ifdef CONFIG_SLAB_FREELIST_HARDENED + BUG_ON(object == fp); /* naive detection of double free or corruption */ +#endif + *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr); } -- 2.7.4
