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

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Message-ID: <20231023-strncpy-drivers-s390-cio-chsc-c-v1-1-8b76a7b83260@google.com>
Date: Mon, 23 Oct 2023 19:24:38 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Vineeth Vijayan <vneethv@...ux.ibm.com>, Peter Oberparleiter <oberpar@...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, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] s390/cio: 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 both `params` and `id` to be NUL-terminated based on their
usage with format strings:

	format_node_data(iuparams, iunodeid, &lir->incident_node);
	format_node_data(auparams, aunodeid, &lir->attached_node);

	switch (lir->iq.class) {
	case LIR_IQ_CLASS_DEGRADED:
		pr_warn("Link degraded: RS=%02x RSID=%04x IC=%02x "
			"IUPARAMS=%s IUNODEID=%s AUPARAMS=%s AUNODEID=%s\n",
			sei_area->rs, sei_area->rsid, lir->ic, iuparams,
			iunodeid, auparams, aunodeid);

NUL-padding is not required as both `params` and `id` have been memset
to 0:

	memset(params, 0, PARAMS_LEN);
	memset(id, 0, NODEID_LEN);

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.

Note that there's no overread bugs in the current implementation as the
string literal "n/a" has a size much smaller than PARAMS_LEN or
NODEID_LEN. Nonetheless, let's favor strscpy().

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/cio/chsc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/cio/chsc.c b/drivers/s390/cio/chsc.c
index 0abd77f4b664..9319f448a6e2 100644
--- a/drivers/s390/cio/chsc.c
+++ b/drivers/s390/cio/chsc.c
@@ -393,8 +393,8 @@ static void format_node_data(char *params, char *id, struct node_descriptor *nd)
 	memset(id, 0, NODEID_LEN);
 
 	if (nd->validity != ND_VALIDITY_VALID) {
-		strncpy(params, "n/a", PARAMS_LEN - 1);
-		strncpy(id, "n/a", NODEID_LEN - 1);
+		strscpy(params, "n/a", PARAMS_LEN);
+		strscpy(id, "n/a", NODEID_LEN);
 		return;
 	}
 

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-cio-chsc-c-3bafdc7535b7

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