linux-hardening - [PATCH] lib/test_string.c: Add test for strlen()

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Date:   Sun, 30 Jan 2022 10:36:53 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Peter Rosin <peda@...ntia.se>,
        Andy Shevchenko <andy@...nel.org>,
        Matteo Croce <mcroce@...rosoft.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: [PATCH] lib/test_string.c: Add test for strlen()

Add a simple test for strlen() functionality, including using it as a
constant expression.

Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Peter Rosin <peda@...ntia.se>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
I'll be taking this as part of my Clang FORTIFY_SOURCE series.
---
 lib/test_string.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/lib/test_string.c b/lib/test_string.c
index 9dfd6f52de92..59994f552c48 100644
--- a/lib/test_string.c
+++ b/lib/test_string.c
@@ -179,6 +179,38 @@ static __init int strnchr_selftest(void)
 	return 0;
 }
 
+/*
+ * Unlike many other string functions, strlen() can be used in
+ * static initializers when string lengths are known at compile
+ * time. (i.e. Under these conditions, strlen() is a constant
+ * expression.) Make sure it can be used this way.
+ */
+static const int strlen_ce = strlen("tada, a constant expression");
+
+static __init int strlen_selftest(void)
+{
+	/* String length ruler:         123456789012345 */
+	static const char normal[]   = "I am normal";
+	static const char *ptr       = "where do I go?";
+	static const char trailing[] = "hidden NULLs\0\0\0";
+	static const char leading[]  = "\0\0hidden text";
+
+	if (strlen(normal) != 11)
+		return 0x100001;
+	if (strlen(ptr++) != 14)
+		return 0x100002;
+	if (strlen(ptr++) != 13)
+		return 0x100003;
+	if (strlen(trailing) != 12)
+		return 0x100004;
+	if (strlen(leading) != 0)
+		return 0x100005;
+	if (strlen_ce != 27)
+		return 0x100006;
+
+	return 0;
+}
+
 static __exit void string_selftest_remove(void)
 {
 }
@@ -212,6 +244,11 @@ static __init int string_selftest_init(void)
 	if (subtest)
 		goto fail;
 
+	test = 5;
+	subtest = strlen_selftest();
+	if (subtest)
+		goto fail;
+
 	pr_info("String selftests succeeded\n");
 	return 0;
 fail:
-- 
2.30.2