[PATCH] lib/test_kasan: Add tests for several string/memory API functions

Andrey Ryabinin
2018-09-06T17:05:56Z

Arch code may have asm implementation of string/memory API functions
instead of using generic one from lib/string.c. KASAN don't see
memory accesses in asm code, thus can miss many bugs.

E.g. on ARM64 KASAN don't see bugs in memchr(), memcmp(), str[r]chr(),
str[n]cmp(), str[n]len(). Add tests for these functions to be sure
that we notice the problem on other architectures.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
lib/test_kasan.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index ec657105edbf..51b78405bf24 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -579,6 +579,73 @@ static noinline void __init kmem_cache_invalid_free(void)
kmem_cache_destroy(cache);
}

+static noinline void __init kasan_memchr(void)
+{
+ char *ptr;
+ size_t size = 24;
+
+ pr_info("out-of-bounds in memchr\n");
+ ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
+ if (!ptr)
+ return;
+
+ memchr(ptr, '1', size + 1);
+ kfree(ptr);
+}
+
+static noinline void __init kasan_memcmp(void)
+{
+ char *ptr;
+ size_t size = 24;
+ int arr[9];
+
+ pr_info("out-of-bounds in memcmp\n");
+ ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
+ if (!ptr)
+ return;
+
+ memset(arr, 0, sizeof(arr));
+ memcmp(ptr, arr, size+1);
+ kfree(ptr);
+}
+
+static noinline void __init kasan_strings(void)
+{
+ char *ptr;
+ size_t size = 24;
+
+ pr_info("use-after-free in strchr\n");
+ ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
+ if (!ptr)
+ return;
+
+ kfree(ptr);
+
+ /*
+ * Try to cause only 1 invalid access (less spam in dmesg).
+ * For that we need ptr to point to zeroed byte.
+ * Skip metadata that could be stored in freed object so ptr
+ * will likely point to zeroed byte.
+ */
+ ptr += 16;
+ strchr(ptr, '1');
+
+ pr_info("use-after-free in strrchr\n");
+ strrchr(ptr, '1');
+
+ pr_info("use-after-free in strcmp\n");
+ strcmp(ptr, "2");
+
+ pr_info("use-after-free in strncmp\n");
+ strncmp(ptr, "2", 1);
+
+ pr_info("use-after-free in strlen\n");
+ strlen(ptr);
+
+ pr_info("use-after-free in strnlen\n");
+ strnlen(ptr, 1);
+}
+
static int __init kmalloc_tests_init(void)
{
/*
@@ -618,6 +685,9 @@ static int __init kmalloc_tests_init(void)
use_after_scope_test();
kmem_cache_double_free();
kmem_cache_invalid_free();
+ kasan_memchr();
+ kasan_memcmp();
+ kasan_strings();

kasan_restore_multi_shot(multishot);

--
2.16.4