On Mon, 2020-08-10 at 08:44 -0400, Qian Cai wrote: > On Mon, Aug 10, 2020 at 07:50:57PM +0800, Walter Wu wrote: > > On Mon, 2020-08-10 at 07:19 -0400, Qian Cai wrote: > > > > > > > On Aug 10, 2020, at 3:21 AM, Walter Wu <walter-zh...@mediatek.com> > > > > 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. > > > > > > > A good debug tool is to have complete information in order to solve > > issue. We should focus on if KASAN reports always show this debug > > information or create a option to decide if show it. Because this > > feature is Dimitry's suggestion. see [1]. So I think it need to be > > implemented. Maybe we can wait his response. > > > > [1]https://lkml.org/lkml/2020/6/23/256 > > I don't know if it is Dmitry's pipe-dream which every KASAN report would > enable > developers to fix it without reproducing it. It is always an ongoing > struggling > between to make kernel easier to debug and the things less cumbersome. > > On the other hand, Dmitry's suggestion makes sense only if the price we are > going to pay is fair. With the current diffstat and the recent experience of > call_rcu() stacks "waste" screen spaces as a heavy KASAN user myself, I can't > really get that exciting for pushing the limit again at all. >
If you are concerned that the report is long, maybe we can create an option for the user decide whether print them (include call_rcu). So this should satisfy everyone? > > > > > > > > > > [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(-) > > > > > > > > -- > > > > 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+unsubscr...@googlegroups.com. > > > > To view this discussion on the web visit > > > > https://groups.google.com/d/msgid/kasan-dev/20200810072115.429-1-walter-zh.wu%40mediatek.com. > >
