[PATCH v2] task_work: kasan: record task_work_add() call stack

[Walter Wu]

Why record task_work_add() call stack?
Syzbot reports many use-after-free issues for task_work, see [1].
After see the free stack and the current auxiliary stack, we think
they are useless, we don't know where register the work, this work
may be the free call stack, so that we miss the root cause and
don't solve the use-after-free.

Add task_work_add() call stack into KASAN auxiliary stack in
order to improve KASAN report. It is useful for programmers
to solve use-after-free issues.

[1]: https://groups.google.com/g/syzkaller-bugs/search?q=kasan%20use-after-free%20task_work_run

Signed-off-by: Walter Wu <walter-zh.wu at mediatek.com>
Suggested-by: Dmitry Vyukov <dvyukov at google.com>
Cc: Andrey Konovalov <andreyknvl at google.com>
Cc: Andrey Ryabinin <ryabinin.a.a at gmail.com>
Cc: Dmitry Vyukov <dvyukov at google.com>
Cc: Alexander Potapenko <glider at google.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Matthias Brugger <matthias.bgg at gmail.com>
Cc: Jens Axboe <axboe at kernel.dk>
Cc: Oleg Nesterov <oleg at redhat.com>
---

v2: Fix kasan_record_aux_stack() calling sequence issue.
    Thanks for Dmitry's suggestion

---
 kernel/task_work.c | 3 +++
 mm/kasan/kasan.h   | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 9cde961875c0..3d4852891fa8 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 {
 	struct callback_head *head;
 
+	/* record the work call stack in order to print it in KASAN reports */
+	kasan_record_aux_stack(work);
+
 	do {
 		head = READ_ONCE(task->task_works);
 		if (unlikely(head == &work_exited))
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3436c6bf7c0c..e4629a971a3c 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -146,7 +146,7 @@ struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
 #ifdef CONFIG_KASAN_GENERIC
 	/*
-	 * call_rcu() call stack is stored into struct kasan_alloc_meta.
+	 * The auxiliary stack is stored into struct kasan_alloc_meta.
 	 * The free stack is stored into struct kasan_free_meta.
 	 */
 	depot_stack_handle_t aux_stack[2];
-- 
2.18.0