linux-kernel - [PATCH 1/3] [v2] staging: rts5208: replace weird strncpy() with memcpy()

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Message-Id: <20240408194821.3183462-1-arnd@kernel.org>
Date: Mon,  8 Apr 2024 21:48:09 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Justin Stitt <justinstitt@...gle.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] [v2] staging: rts5208: 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);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The code originally had a memcpy() that would overread the source string,
and commit 88a5b39b69ab ("staging/rts5208: Fix read overflow in memcpy")
fixed this but introduced the warning about truncation in the process.

As Dan points out, the final space in the inquiry_string always gets
cut off, so remove it here for clarity, leaving exactly the 28 non-NUL
characters that can get copied into the output. In the 'pro_formatter_flag'
this is followed by another 20 bytes from the 'formatter_inquiry_str'
array, but there the output never contains a NUL-termination, and the
length is known, so memcpy() is the more logical choice.

Cc: Dan Carpenter <dan.carpenter@...aro.org>
Link: https://lore.kernel.org/lkml/695be581-548f-4e5e-a211-5f3b95568e77@moroto.mountain/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v2: remove unneeded space byte from input string for clarity,
    rework changelog text
---
 drivers/staging/rts5208/rtsx_scsi.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/rts5208/rtsx_scsi.c b/drivers/staging/rts5208/rtsx_scsi.c
index 08bd768ad34d..c27cffb9ad8f 100644
--- a/drivers/staging/rts5208/rtsx_scsi.c
+++ b/drivers/staging/rts5208/rtsx_scsi.c
@@ -463,10 +463,10 @@ static unsigned char formatter_inquiry_str[20] = {
 static int inquiry(struct scsi_cmnd *srb, struct rtsx_chip *chip)
 {
 	unsigned int lun = SCSI_LUN(srb);
-	char *inquiry_default = (char *)"Generic-xD/SD/M.S.      1.00 ";
-	char *inquiry_sdms =    (char *)"Generic-SD/MemoryStick  1.00 ";
-	char *inquiry_sd =      (char *)"Generic-SD/MMC          1.00 ";
-	char *inquiry_ms =      (char *)"Generic-MemoryStick     1.00 ";
+	char *inquiry_default = (char *)"Generic-xD/SD/M.S.      1.00";
+	char *inquiry_sdms =    (char *)"Generic-SD/MemoryStick  1.00";
+	char *inquiry_sd =      (char *)"Generic-SD/MMC          1.00";
+	char *inquiry_ms =      (char *)"Generic-MemoryStick     1.00";
 	char *inquiry_string;
 	unsigned char sendbytes;
 	unsigned char *buf;
@@ -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