linux-kernel - [PATCH 7/8] kasan: test: avoid corrupting memory in copy_user

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Message-Id: <17b812a3c28024acfca9b1a9e45c8235b35efa32.1628709663.git.andreyknvl@gmail.com>
Date:   Wed, 11 Aug 2021 21:30:06 +0200
From:   andrey.konovalov@...ux.dev
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 7/8] kasan: test: avoid corrupting memory in copy_user_test

From: Andrey Konovalov <andreyknvl@...il.com>

copy_user_test() does writes past the allocated object. As the result,
it corrupts kernel memory, which might lead to crashes with the HW_TAGS
mode, as it neither uses quarantine nor redzones.

(Technically, this test can't yet be enabled with the HW_TAGS mode, but
this will be implemented in the future.)

Adjust the test to only write memory within the aligned kmalloc object.

Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>
---
 lib/test_kasan_module.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
index f1017f345d6c..fa73b9df0be4 100644
--- a/lib/test_kasan_module.c
+++ b/lib/test_kasan_module.c
@@ -15,13 +15,11 @@
 
 #include "../mm/kasan/kasan.h"
 
-#define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : KASAN_GRANULE_SIZE)
-
 static noinline void __init copy_user_test(void)
 {
 	char *kmem;
 	char __user *usermem;
-	size_t size = 10;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 	int __maybe_unused unused;
 
 	kmem = kmalloc(size, GFP_KERNEL);
@@ -38,25 +36,25 @@ static noinline void __init copy_user_test(void)
 	}
 
 	pr_info("out-of-bounds in copy_from_user()\n");
-	unused = copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
+	unused = copy_from_user(kmem, usermem, size + 1);
 
 	pr_info("out-of-bounds in copy_to_user()\n");
-	unused = copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
+	unused = copy_to_user(usermem, kmem, size + 1);
 
 	pr_info("out-of-bounds in __copy_from_user()\n");
-	unused = __copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
+	unused = __copy_from_user(kmem, usermem, size + 1);
 
 	pr_info("out-of-bounds in __copy_to_user()\n");
-	unused = __copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
+	unused = __copy_to_user(usermem, kmem, size + 1);
 
 	pr_info("out-of-bounds in __copy_from_user_inatomic()\n");
-	unused = __copy_from_user_inatomic(kmem, usermem, size + 1 + OOB_TAG_OFF);
+	unused = __copy_from_user_inatomic(kmem, usermem, size + 1);
 
 	pr_info("out-of-bounds in __copy_to_user_inatomic()\n");
-	unused = __copy_to_user_inatomic(usermem, kmem, size + 1 + OOB_TAG_OFF);
+	unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
 
 	pr_info("out-of-bounds in strncpy_from_user()\n");
-	unused = strncpy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
+	unused = strncpy_from_user(kmem, usermem, size + 1);
 
 	vm_munmap((unsigned long)usermem, PAGE_SIZE);
 	kfree(kmem);
-- 
2.25.1