Re: [PATCH 0/5] kasan: add workqueue and timer stack for generic KASAN
From: Qian Cai
Date: Mon Aug 10 2020 - 07:19:45 EST
> On Aug 10, 2020, at 3:21 AM, Walter Wu <walter-zh.wu@xxxxxxxxxxxx> wrote:
> Syzbot reports many UAF issues for workqueue or timer, see  and .
> 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.
> 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.
> Generic KASAN will record the last two workqueue and timer stacks,
> print them in KASAN report. It is only suitable for generic KASAN.
> 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.
> 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 would argue that it only make sense to complicate it if it is useful most of the time which I never feel or hear that is the case. This reminds me your recent call_rcu() stacks that most of time just makes parsing the report cumbersome. Thus, I urge this exercise to over-engineer on special cases need to stop entirely.
> 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
> 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(-)
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@xxxxxxxxxxxxxxxx.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20200810072115.429-1-walter-zh.wu%40mediatek.com.