lib/test_kasan: Add test for double-kzfree detection

Add a simple test that checks if double-kzfree is being detected
correctly.

Link: http://lkml.kernel.org/r/20190626142014.141844-4-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kasan.c

@@ -693,6 +693,22 @@ static noinline void __init kasan_bitops(void)
 	kfree(bits);
 }
 
+static noinline void __init kmalloc_double_kzfree(void)
+{
+	char *ptr;
+	size_t size = 16;
+
+	pr_info("double-free (kzfree)\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	kzfree(ptr);
+	kzfree(ptr);
+}
+
 static int __init kmalloc_tests_init(void)
 {
 	/*
@@ -735,6 +751,7 @@ static int __init kmalloc_tests_init(void)
 	kasan_memcmp();
 	kasan_strings();
 	kasan_bitops();
+	kmalloc_double_kzfree();
 
 	kasan_restore_multi_shot(multishot);