[PATCH v4 4/6] kasan: add tests for timer stack recording

[Walter Wu <walter-zh.wu@xxxxxxxxxxxx>]

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

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

 BUG: KASAN: use-after-free in kasan_timer_uaf

 Freed by task 0:
  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_timer_function+0x1c/0x28

 Last potentially related work creation:
  kasan_save_stack+0x24/0x50
  kasan_record_tmr_stack+0xa8/0xb8
  init_timer_key+0xf0/0x248
  kasan_timer_uaf+0x5c/0xd8

Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
---

v4:
- testcase has merge conflict, so that rebase onto the KASAN-KUNIT

---
 lib/test_kasan_module.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
index 2d68db6ae67b..d8234a1db8c9 100644
--- a/lib/test_kasan_module.c
+++ b/lib/test_kasan_module.c
@@ -12,6 +12,7 @@
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
+#include <linux/delay.h>
 
 #include "../mm/kasan/kasan.h"
 
@@ -91,6 +92,29 @@ static noinline void __init kasan_rcu_uaf(void)
 	call_rcu(&global_rcu_ptr->rcu, kasan_rcu_reclaim);
 }
 
+static noinline void __init kasan_timer_function(struct timer_list *timer)
+{
+	del_timer(timer);
+	kfree(timer);
+}
+
+static noinline void __init kasan_timer_uaf(void)
+{
+	struct timer_list *timer;
+
+	timer = kmalloc(sizeof(struct timer_list), GFP_KERNEL);
+	if (!timer) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	timer_setup(timer, kasan_timer_function, 0);
+	add_timer(timer);
+	msleep(100);
+
+	pr_info("use-after-free on timer\n");
+	((volatile struct timer_list *)timer)->expires;
+}
 
 static int __init test_kasan_module_init(void)
 {
@@ -102,6 +126,7 @@ static int __init test_kasan_module_init(void)
 
 	copy_user_test();
 	kasan_rcu_uaf();
+	kasan_timer_uaf();
 
 	kasan_restore_multi_shot(multishot);
 	return -EAGAIN;
-- 
2.18.0