linux-hardening - [PATCH] s390/ctcm: replace deprecated strncpy with strscpy

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Date: Mon, 23 Oct 2023 19:35:07 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Alexandra Winter <wintera@...ux.ibm.com>, Wenjia Zhang <wenjia@...ux.ibm.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] s390/ctcm: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect chid to be NUL-terminated based on its use with format
strings:

	CTCM_DBF_TEXT_(SETUP, CTC_DBF_INFO, "%s(%s) %s", CTCM_FUNTAIL,
			chid, ok ? "OK" : "failed");

Moreover, NUL-padding is not required as it is _only_ used in this one
instance with a format string.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

We can also drop the +1 from chid's declaration as we no longer need to
be cautious about leaving a spot for a NUL-byte. Let's use the more
idiomatic strscpy usage of (dest, src, sizeof(dest)) as this more
closely ties the destination buffer to the length.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/s390/net/ctcm_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c
index 6faf27136024..ac15d7c2b200 100644
--- a/drivers/s390/net/ctcm_main.c
+++ b/drivers/s390/net/ctcm_main.c
@@ -200,13 +200,13 @@ static void channel_free(struct channel *ch)
 static void channel_remove(struct channel *ch)
 {
 	struct channel **c = &channels;
-	char chid[CTCM_ID_SIZE+1];
+	char chid[CTCM_ID_SIZE];
 	int ok = 0;
 
 	if (ch == NULL)
 		return;
 	else
-		strncpy(chid, ch->id, CTCM_ID_SIZE);
+		strscpy(chid, ch->id, sizeof(chid));
 
 	channel_free(ch);
 	while (*c) {

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-net-ctcm_main-c-f9180f470c69

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