Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory debugger.

From: Ingo Molnar
Date: Thu Nov 20 2014 - 04:12:30 EST

* Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> 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:
> (sched/numa: Fix out of bounds read in sched_init_numa())
> (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.


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