linux-hardening - [PATCH] scsi: lpfc: replace deprecated strncpy with strscpy

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Message-ID: <20240222-strncpy-drivers-scsi-lpfc-lpfc_ct-c-v1-1-20c685bd1b43@google.com>
Date: Thu, 22 Feb 2024 00:41:52 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: James Smart <james.smart@...adcom.com>, Dick Kennedy <dick.kennedy@...adcom.com>, 
	"James E.J. Bottomley" <jejb@...ux.ibm.com>, "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] scsi: lpfc: 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 ae->value_string to be NUL-terminated because there's a
comment that says as much; these attr strings are also used with other
string APIs, further cementing the fact.

Now, the question of whether or not to NUL-pad the destination buffer:
lpfc_fdmi_rprt_defer() initializes vports (all zero-initialized), then
we call lpfc_fdmi_cmd() with each vport and a mask. Then, inside of
lpfc_fdmi_cmd() we check each bit in the mask to invoke the proper
callback. Importantly, the zero-initialized vport is passed in as the
"attr" parameter. Seeing this:
|	struct lpfc_fdmi_attr_string *ae = attr;
... we can tell that ae->value_string is entirely zero-initialized. Due
to this, NUL-padding is _not_ required as it would be redundant.

Conveniently, strscpy also returns the number of bytes copied into the
destination buffer, eliminating the need for strnlen!

Considering the above, a suitable replacement is `strscpy` [2].

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>
---
 drivers/scsi/lpfc/lpfc_ct.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/lpfc/lpfc_ct.c b/drivers/scsi/lpfc/lpfc_ct.c
index baae1f8279e0..42594ec87290 100644
--- a/drivers/scsi/lpfc/lpfc_ct.c
+++ b/drivers/scsi/lpfc/lpfc_ct.c
@@ -2569,9 +2569,8 @@ lpfc_fdmi_set_attr_string(void *attr, uint16_t attrtype, char *attrstring)
 	 * 64 bytes or less.
 	 */

-	strncpy(ae->value_string, attrstring, sizeof(ae->value_string));
-	len = strnlen(ae->value_string, sizeof(ae->value_string));
-	/* round string length to a 32bit boundary. Ensure there's a NULL */
+	len = strscpy(ae->value_string, attrstring, sizeof(ae->value_string));
+	/* round string length to a 32bit boundary */
 	len += (len & 3) ? (4 - (len & 3)) : 4;
 	/* size is Type/Len (4 bytes) plus string length */
 	size = FOURBYTES + len;

---
base-commit: 39133352cbed6626956d38ed72012f49b0421e7b
change-id: 20240222-strncpy-drivers-scsi-lpfc-lpfc_ct-c-f54b67eeeb68

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