linux-hardening - [PATCH] tomoyo: refactor deprecated strncpy

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Date:   Thu, 03 Aug 2023 21:33:44 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Kentaro Takeda <takedakn@...data.co.jp>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] tomoyo: refactor deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on its destination buffer argument which is
_not_ the case for `strncpy`!

It should be noted that the destination buffer is zero-initialized and
had a max length of `sizeof(dest) - 1`. There is likely _not_ a bug
present in the current implementation. However, by switching to
`strscpy` we get the benefit of no longer needing the `- 1`'s from the
string copy invocations on top of `strscpy` being a safer interface all
together.

[1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
[2]: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html

Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
 security/tomoyo/domain.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index ac20c0bdff9d..90b53500a236 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -784,13 +784,12 @@ int tomoyo_find_next_domain(struct linux_binprm *bprm)
 		if (!strcmp(domainname, "parent")) {
 			char *cp;
 
-			strncpy(ee->tmp, old_domain->domainname->name,
-				TOMOYO_EXEC_TMPSIZE - 1);
+			strscpy(ee->tmp, old_domain->domainname->name, TOMOYO_EXEC_TMPSIZE);
 			cp = strrchr(ee->tmp, ' ');
 			if (cp)
 				*cp = '\0';
 		} else if (*domainname == '<')
-			strncpy(ee->tmp, domainname, TOMOYO_EXEC_TMPSIZE - 1);
+			strscpy(ee->tmp, domainname, TOMOYO_EXEC_TMPSIZE);
 		else
 			snprintf(ee->tmp, TOMOYO_EXEC_TMPSIZE - 1, "%s %s",
 				 old_domain->domainname->name, domainname);

---
base-commit: 5d0c230f1de8c7515b6567d9afba1f196fb4e2f4
change-id: 20230803-security-tomoyo-7d58f53d35a6

Best regards,
--
Justin Stitt <justinstitt@...gle.com>