linux-hardening - [PATCH] lkdtm/fortify: Swap memcpy() for strncpy()

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Message-Id: <20220216202548.2093883-1-keescook@chromium.org>
Date:   Wed, 16 Feb 2022 12:25:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] lkdtm/fortify: Swap memcpy() for strncpy()

The memcpy() runtime defenses are still not landed, so test with
strncpy() for now.

Reported-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/misc/lkdtm/fortify.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/lkdtm/fortify.c b/drivers/misc/lkdtm/fortify.c
index d06458a4858e..ab33bb5e2e7a 100644
--- a/drivers/misc/lkdtm/fortify.c
+++ b/drivers/misc/lkdtm/fortify.c
@@ -44,14 +44,14 @@ void lkdtm_FORTIFIED_SUBOBJECT(void)
 	strscpy(src, "over ten bytes", size);
 	size = strlen(src) + 1;
 
-	pr_info("trying to strcpy past the end of a member of a struct\n");
+	pr_info("trying to strncpy past the end of a member of a struct\n");
 
 	/*
-	 * memcpy(target.a, src, 20); will hit a compile error because the
+	 * strncpy(target.a, src, 20); will hit a compile error because the
 	 * compiler knows at build time that target.a < 20 bytes. Use a
 	 * volatile to force a runtime error.
 	 */
-	memcpy(target.a, src, size);
+	strncpy(target.a, src, size);
 
 	/* Store result to global to prevent the code from being eliminated */
 	fortify_scratch_space = target.a[3];
-- 
2.30.2