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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH 0/5] kasan: add workqueue and timer stack for generic KASAN
Date:   Mon, 10 Aug 2020 07:19:35 -0400
Message-Id: <B873B364-FF03-4819-8F9C-79F3C4EF47CE@lca.pw>
References: <20200810072115.429-1-walter-zh.wu@mediatek.com>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        John Stultz <john.stultz@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        wsd_upstream <wsd_upstream@mediatek.com>,
        linux-mediatek@lists.infradead.org
In-Reply-To: <20200810072115.429-1-walter-zh.wu@mediatek.com>
To:     Walter Wu <walter-zh.wu@mediatek.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Aug 10, 2020, at 3:21 AM, Walter Wu <walter-zh.wu@mediatek.com> wrote:
>=20
> =EF=BB=BFSyzbot reports many UAF issues for workqueue or timer, see [1] an=
d [2].
> In some of these access/allocation happened in process_one_work(),
> we see the free stack is useless in KASAN report, it doesn't help
> programmers to solve UAF on workqueue. The same may stand for times.
>=20
> This patchset improves KASAN reports by making them to have workqueue
> queueing stack and timer queueing stack information. It is useful for
> programmers to solve use-after-free or double-free memory issue.
>=20
> Generic KASAN will record the last two workqueue and timer stacks,
> print them in KASAN report. It is only suitable for generic KASAN.
>=20
> In order to print the last two workqueue and timer stacks, so that
> we add new members in struct kasan_alloc_meta.
> - two workqueue queueing work stacks, total size is 8 bytes.
> - two timer queueing stacks, total size is 8 bytes.
>=20
> Orignial struct kasan_alloc_meta size is 16 bytes. After add new
> members, then the struct kasan_alloc_meta total size is 32 bytes,
> It is a good number of alignment. Let it get better memory consumption.

Getting debugging tools complicated surely is the best way to kill it. I wou=
ld argue that it only make sense to complicate it if it is useful most of th=
e time which I never feel or hear that is the case. This reminds me your rec=
ent call_rcu() stacks that most of time just makes parsing the report cumber=
some. Thus, I urge this exercise to over-engineer on special cases need to s=
top entirely.

>=20
> [1]https://groups.google.com/g/syzkaller-bugs/search?q=3D%22use-after-free=
%22+process_one_work
> [2]https://groups.google.com/g/syzkaller-bugs/search?q=3D%22use-after-free=
%22%20expire_timers
> [3]https://bugzilla.kernel.org/show_bug.cgi?id=3D198437
>=20
> Walter Wu (5):
> timer: kasan: record and print timer stack
> workqueue: kasan: record and print workqueue stack
> lib/test_kasan.c: add timer test case
> lib/test_kasan.c: add workqueue test case
> kasan: update documentation for generic kasan
>=20
> Documentation/dev-tools/kasan.rst |  4 ++--
> include/linux/kasan.h             |  4 ++++
> kernel/time/timer.c               |  2 ++
> kernel/workqueue.c                |  3 +++
> lib/test_kasan.c                  | 54 +++++++++++++++++++++++++++++++++++=
+++++++++++++++++++
> mm/kasan/generic.c                | 42 +++++++++++++++++++++++++++++++++++=
+++++++
> mm/kasan/kasan.h                  |  6 +++++-
> mm/kasan/report.c                 | 22 ++++++++++++++++++++++
> 8 files changed, 134 insertions(+), 3 deletions(-)
>=20
> --=20
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