Date: Thu, 20 Nov 2014 10:03:56 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <a.ryabinin@samsung.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Chernenkov <dmitryc@google.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Michal Marek <mmarek@suse.cz>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>,
        Vegard Nossum <vegard.nossum@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Dave Jones <davej@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
        Joe Perches <joe@perches.com>, LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory
 debugger.
Message-ID: <20141120090356.GA6690@gmail.com>
References: <1404905415-9046-1-git-send-email-a.ryabinin@samsung.com>
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 <5461B906.1040803@samsung.com>
 <20141118125843.434c216540def495d50f3a45@linux-foundation.org>
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* Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:

> I've counted 16:
> 
> aab515d (fib_trie: remove potential out of bound access)
> 984f173 ([SCSI] sd: Fix potential out-of-bounds access)
> 5e9ae2e (aio: fix use-after-free in aio_migratepage)
> 2811eba (ipv6: udp packets following an UFO enqueued packet need also
> be handled by UFO)
> 057db84 (tracing: Fix potential out-of-bounds in trace_get_user())
> 9709674 (ipv4: fix a race in ip4_datagram_release_cb())
> 4e8d213 (ext4: fix use-after-free in ext4_mb_new_blocks)
> 624483f (mm: rmap: fix use-after-free in __put_anon_vma)
> 93b7aca (lib/idr.c: fix out-of-bounds pointer dereference)
> b4903d6 (mm: debugfs: move rounddown_pow_of_two() out from do_fault path)
> 40eea80 (net: sendmsg: fix NULL pointer dereference)
> 10ec947 (ipv4: fix buffer overflow in ip_options_compile())
> dbf20cb2 (f2fs: avoid use invalid mapping of node_inode when evict meta inode)
> d6d86c0 (mm/balloon_compaction: redesign ballooned pages management)
> 
> + 2 recently found, seems minor:
>     http://lkml.kernel.org/r/1415372020-1871-1-git-send-email-a.ryabinin@samsung.com
>     (sched/numa: Fix out of bounds read in sched_init_numa())
> 
>     http://lkml.kernel.org/r/1415458085-12485-1-git-send-email-ryabinin.a.a@gmail.com
>     (security: smack: fix out-of-bounds access in smk_parse_smack())
> 
> Note that some functionality is not yet implemented in this 
> patch set. Kasan has possibility to detect out-of-bounds 
> accesses on global/stack variables. Neither 
> kmemcheck/debug_pagealloc or slub_debug could do that.
> 
> > That's in a 20-year-old code base, so one new minor bug discovered per
> > three years?  Not worth it!
> >
> > Presumably more bugs will be exposed as more people use kasan on
> > different kernel configs, but will their number and seriousness justify
> > the maintenance effort?
> >
> 
> Yes, AFAIK there are only few users of kasan now, and I guess that
> only small part of kernel code
> was covered by it.
> IMO kasan shouldn't take a lot maintenance efforts, most part of code
> is isolated and it doesn't
> have some complex dependencies on in-kernel API.
> And you could always just poke me, I'd be happy to sort out any issues.
> 
> > If kasan will permit us to remove kmemcheck/debug_pagealloc/slub_debug
> > then that tips the balance a little.  What's the feasibility of that?
> >
> 
> I think kasan could replace kmemcheck at some point.

So that angle sounds interesting, because kmemcheck is 
essentially unmaintained right now: in the last 3 years since 
v3.0 arch/x86/mm/kmemcheck/ has not seen a single kmemcheck 
specific change, only 4 incidental changes.

kmemcheck is also very architecture bound and somewhat fragile 
due to having to decode instructions, so if generic, compiler 
driven instrumentation can replace it, that would be a plus.

Thanks,

	Ingo
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