lib/test_kasan.c: add workqueue test case

Adds a test to verify workqueue stack recording and print it in
KASAN report.

The KASAN report was as follows(cleaned up slightly):

 BUG: KASAN: use-after-free in kasan_workqueue_uaf

 Freed by task 54:
  kasan_save_stack+0x24/0x50
  kasan_set_track+0x24/0x38
  kasan_set_free_info+0x20/0x40
  __kasan_slab_free+0x10c/0x170
  kasan_slab_free+0x10/0x18
  kfree+0x98/0x270
  kasan_workqueue_work+0xc/0x18

 Last potentially related work creation:
  kasan_save_stack+0x24/0x50
  kasan_record_wq_stack+0xa8/0xb8
  insert_work+0x48/0x288
  __queue_work+0x3e8/0xc40
  queue_work_on+0xf4/0x118
  kasan_workqueue_uaf+0xfc/0x190

Link: https://lkml.kernel.org/r/20201203022748.30681-1-walter-zh.wu@mediatek.comSigned-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Acked-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kasan_module.c

@@ -91,6 +91,34 @@ static noinline void __init kasan_rcu_uaf(void)
 	call_rcu(&global_rcu_ptr->rcu, kasan_rcu_reclaim);
 }
 
+static noinline void __init kasan_workqueue_work(struct work_struct *work)
+{
+	kfree(work);
+}
+
+static noinline void __init kasan_workqueue_uaf(void)
+{
+	struct workqueue_struct *workqueue;
+	struct work_struct *work;
+
+	workqueue = create_workqueue("kasan_wq_test");
+	if (!workqueue) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+	work = kmalloc(sizeof(struct work_struct), GFP_KERNEL);
+	if (!work) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	INIT_WORK(work, kasan_workqueue_work);
+	queue_work(workqueue, work);
+	destroy_workqueue(workqueue);
+
+	pr_info("use-after-free on workqueue\n");
+	((volatile struct work_struct *)work)->data;
+}
 
 static int __init test_kasan_module_init(void)
 {
@@ -102,6 +130,7 @@ static int __init test_kasan_module_init(void)
 
 	copy_user_test();
 	kasan_rcu_uaf();
+	kasan_workqueue_uaf();
 
 	kasan_restore_multi_shot(multishot);
 	return -EAGAIN;