kasan: record task_work_add() call stack

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

Add the task_work_add() call stack into the KASAN auxiliary stack in order
to improve KASAN reports.  It helps programmers solve use-after-free
issues.

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

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Walter Wu <[email protected]>
Suggested-by: Dmitry Vyukov <[email protected]>
Reviewed-by: Dmitry Vyukov <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Acked-by: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Matthias Brugger <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 4 insertions, 1 deletions

diff --git a/kernel/task_work.c b/kernel/task_work.c
index e9316198c64b..1698fbe6f0e1 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 071c456a3579..3820ca54743b 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -163,7 +163,7 @@ 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];