linux-kernel - [PATCH] scsi: myrb: fix sprintf buffer overflow warning

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Date:   Fri,  2 Nov 2018 16:34:49 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Hannes Reinecke <hare@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] scsi: myrb: fix sprintf buffer overflow warning

gcc warns that the 12 byte fw_version field might not be long enough to
contain the generated firmware name string:

drivers/scsi/myrb.c: In function 'myrb_get_hba_config':
drivers/scsi/myrb.c:1052:38: error: '%02d' directive writing between 2 and 3 bytes into a region of size between 2 and 5 [-Werror=format-overflow=]
  sprintf(cb->fw_version, "%d.%02d-%c-%02d",
                                      ^~~~
drivers/scsi/myrb.c:1052:26: note: directive argument in the range [0, 255]
  sprintf(cb->fw_version, "%d.%02d-%c-%02d",
                          ^~~~~~~~~~~~~~~~~
drivers/scsi/myrb.c:1052:2: note: 'sprintf' output between 10 and 14 bytes into a destination of size 12
  sprintf(cb->fw_version, "%d.%02d-%c-%02d",
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   enquiry2->fw.major_version,
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~
   enquiry2->fw.minor_version,
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~
   enquiry2->fw.firmware_type,
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~
   enquiry2->fw.turn_id);
   ~~~~~~~~~~~~~~~~~~~~~

I have not checked whether there are appropriate range checks before the
sprintf, but there is a range check after it that will bail out in case
of out of range version numbers. This means we can simply use snprintf()
instead of sprintf() to limit the output buffer size, and it will work
correctly.

Fixes: 081ff398c56c ("scsi: myrb: Add Mylex RAID controller (block interface)")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/scsi/myrb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/myrb.c b/drivers/scsi/myrb.c
index aeb282f617c5..0642f2d0a3bb 100644
--- a/drivers/scsi/myrb.c
+++ b/drivers/scsi/myrb.c
@@ -1049,7 +1049,8 @@ static int myrb_get_hba_config(struct myrb_hba *cb)
 		enquiry2->fw.firmware_type = '0';
 		enquiry2->fw.turn_id = 0;
 	}
-	sprintf(cb->fw_version, "%d.%02d-%c-%02d",
+	snprintf(cb->fw_version, sizeof(cb->fw_version),
+		"%d.%02d-%c-%02d",
 		enquiry2->fw.major_version,
 		enquiry2->fw.minor_version,
 		enquiry2->fw.firmware_type,
-- 
2.18.0