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

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Message-ID: <20231023-strncpy-drivers-s390-net-qeth_core_main-c-v1-1-e7ce65454446@google.com>
Date: Mon, 23 Oct 2023 19:39:39 +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/qeth: 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 new_entry->dbf_name to be NUL-terminated based on its use with
strcmp():
|       if (strcmp(entry->dbf_name, name) == 0) {

Moreover, NUL-padding is not required as new_entry is kzalloc'd just
before this assignment:
|       new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);

... rendering any future NUL-byte assignments (like the ones strncpy()
does) redundant.

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.

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/qeth_core_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index cd783290bde5..6af2511e070c 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -6226,7 +6226,7 @@ static int qeth_add_dbf_entry(struct qeth_card *card, char *name)
 	new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
 	if (!new_entry)
 		goto err_dbg;
-	strncpy(new_entry->dbf_name, name, DBF_NAME_LEN);
+	strscpy(new_entry->dbf_name, name, sizeof(new_entry->dbf_name));
 	new_entry->dbf_info = card->debug;
 	mutex_lock(&qeth_dbf_list_mutex);
 	list_add(&new_entry->dbf_list, &qeth_dbf_list);

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-net-qeth_core_main-c-0b0ee08672ec

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