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

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Date: Wed, 21 Feb 2024 18:37:48 -0800
From: Kees Cook <kees@...nel.org>
To: Justin Stitt <justinstitt@...gle.com>, 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
Subject: Re: [PATCH] scsi: lpfc: replace deprecated strncpy with strscpy



On February 21, 2024 4:41:52 PM PST, Justin Stitt <justinstitt@...gle.com> wrote:
>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));

This could be < 0 on error, and at least lpfc_fdmi_hba_attr_os_ver() may present more than 64 bytes...

-Kees


>+	/* 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>
>
>

-- 
Kees Cook