lib/test_kasan.c: add tests for several string/memory API functions

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.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Kyeongdon Kim <[email protected]>
Cc: Mark Rutland <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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);