Re: [PATCH 0/5] kasan: add workqueue and timer stack for generic KASAN

[Qian Cai]

> 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 [1] and [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.
> 
> 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.

> 
> [1]https://groups.google.com/g/syzkaller-bugs/search?q=%22use-after-free%22+process_one_work
> [2]https://groups.google.com/g/syzkaller-bugs/search?q=%22use-after-free%22%20expire_timers
> [3]https://bugzilla.kernel.org/show_bug.cgi?id=198437
> 
> 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(-)
> 
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