On Aug 10, 2020, at 3:21 AM, Walter Wu [off-list ref] 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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