Re: [lkp-robot] [printk] 7f7c60e066: BUG:KASAN:slab-out-of-bounds

From: Kees Cook <keescook@chromium.org>
To: "Tobin C. Harding" <me@tobin.cc>
Cc: kernel test robot <xiaolong.ye@intel.com>,
	kernel-hardening@lists.openwall.com,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Tycho Andersen <tycho@docker.com>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	Tejun Heo <tj@kernel.org>,
	Jordan Glover <Golden_Miller83@protonmail.ch>,
	Greg KH <gregkh@linuxfoundation.org>,
	Petr Mladek <pmladek@suse.com>, Joe Perches <joe@perches.com>,
	Ian Campbell <ijc@hellion.org.uk>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <wilal.deacon@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Chris Fries <cfries@google.com>,
	Dave Weinstein <olorin@google.com>,
	Daniel Micay <danielmicay@gmail.com>,
	Djalal Harouni <tixxdz@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>, LKP <lkp@01.org>
Subject: Re: [lkp-robot] [printk] 7f7c60e066: BUG:KASAN:slab-out-of-bounds
Date: Mon, 30 Oct 2017 17:14:59 -0700	[thread overview]
Message-ID: <CAGXu5jJ+oVhroQHcbbiKERqYQXmoMtsmP_QuQwJX9TdAOdtYvQ@mail.gmail.com> (raw)
In-Reply-To: <20171025162213.GH3294@yexl-desktop>

On Wed, Oct 25, 2017 at 9:22 AM, kernel test robot
<xiaolong.ye@intel.com> wrote:
>
> FYI, we noticed the following commit (built with gcc-4.9):
>
> commit: 7f7c60e0663645e757e520245606fde9c6e326bb ("printk: hash addresses printed with %p")
> url: https://github.com/0day-ci/linux/commits/Tobin-C-Harding/printk-hash-addresses-printed-with-p/20171024-231922

It's not clear to me which of the various versions this test ran
against, but it seems like the printf self-tests got very confused by
the results:

> [   40.275423] test_printf: kvasprintf(..., "%p %p", ...) returned '3cf9adbe eff717bf', expected '0000000001234567 fffffffffedcba98'
> [   40.296739] test_printf: vsnprintf(buf, 256, "|%-*p|%*p|", ...) returned 19, expected 39
> [   40.322776] test_printf: vsnprintf(buf, 16, "|%-*p|%*p|", ...) returned 19, expected 39
> [   40.334834] test_printf: vsnprintf(buf, 0, "|%-*p|%*p|", ...) returned 19, expected 39

I assume v10 will fix the width issues, but probably not the value tests...

And it claims a use-after-free, too:

> [   39.757461] The buggy address belongs to the object at 22cb34bb
> [   39.757461]  which belongs to the cache kmalloc-32 of size 32
> [   39.757461] The buggy address is located 0 bytes inside of
> [   39.757461]  32-byte region [22cb34bb, 24ac3a60)

Which becomes rather unreadable, since the address got hashed. :P

-Kees

-- 
Kees Cook
Pixel Security