linux-kernel - [PATCH 03/11] staging: replace weird strncpy() with memcpy()

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Date: Thu, 28 Mar 2024 15:04:47 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Daniel Micay <danielmicay@...il.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	linux-staging@...ts.linux.dev
Subject: [PATCH 03/11] staging: replace weird strncpy() with memcpy()

From: Arnd Bergmann <arnd@...db.de>

When -Wstringop-truncation is enabled, gcc finds a function that
always does a short copy:

In function 'inquiry',
    inlined from 'rtsx_scsi_handler' at drivers/staging/rts5208/rtsx_scsi.c:3210:12:
drivers/staging/rts5208/rtsx_scsi.c:526:17: error: 'strncpy' output truncated copying between 1 and 28 bytes from a string of length 28 [-Werror=stringop-truncation]
  526 |                 strncpy(buf + 8, inquiry_string, sendbytes - 8);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Since the actual size of the copy is already known at this point, just
copy the bytes directly and skip the length check and zero-padding.

This partially reverts an earlier bugfix that replaced the original
incorrect memcpy() with a less bad strncpy(), but it now also avoids
the original overflow.

Fixes: 88a5b39b69ab ("staging/rts5208: Fix read overflow in memcpy")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/staging/rts5208/rtsx_scsi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/rts5208/rtsx_scsi.c b/drivers/staging/rts5208/rtsx_scsi.c
index 08bd768ad34d..a73b0959f5a9 100644
--- a/drivers/staging/rts5208/rtsx_scsi.c
+++ b/drivers/staging/rts5208/rtsx_scsi.c
@@ -523,7 +523,7 @@ static int inquiry(struct scsi_cmnd *srb, struct rtsx_chip *chip)
 
 	if (sendbytes > 8) {
 		memcpy(buf, inquiry_buf, 8);
-		strncpy(buf + 8, inquiry_string, sendbytes - 8);
+		memcpy(buf + 8, inquiry_string, min(sendbytes, 36) - 8);
 		if (pro_formatter_flag) {
 			/* Additional Length */
 			buf[4] = 0x33;
-- 
2.39.2