[PATCH] [v2] scsi: ipr: work around fortify-string warning

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

The ipr_log_vpd_compact() function triggers a fortified memcpy() warning
about a potential string overflow with all versions of clang:

In file included from drivers/scsi/ipr.c:43:
In file included from include/linux/string.h:254:
include/linux/fortify-string.h:520:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __write_overflow_field(p_size_field, size);
                        ^
include/linux/fortify-string.h:520:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
2 errors generated.

I don't see anything actually wrong with the function, but this is the
only instance I can reproduce of the fortification going wrong in the
kernel at the moment, so the easiest solution may be to rewrite the
function into something that does not trigger the warning.

Instead of having a combined buffer for vendor/device/serial strings,
use three separate local variables and just truncate the whitespace
individually.

Fixes: 8cf093e275d0 ("[SCSI] ipr: Improved dual adapter errors")
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
I did not try to bisect which commit introduced this behavior into
the fortified memcpy(), the Fixes: commit is the one that introduced
the ipr_log_vpd_compact() function but this predates the fortified
string helpers.

v2 changes:
- fix off-by-one error
---
 drivers/scsi/ipr.c | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index 198d3f20d682..f1f61705ccd5 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -1516,23 +1516,22 @@ static void ipr_process_ccn(struct ipr_cmnd *ipr_cmd)
 }
 
 /**
- * strip_and_pad_whitespace - Strip and pad trailing whitespace.
- * @i:		index into buffer
- * @buf:		string to modify
+ * strip_whitespace - Strip and pad trailing whitespace.
+ * @i:		size of buffer
+ * @buf:	string to modify
  *
- * This function will strip all trailing whitespace, pad the end
- * of the string with a single space, and NULL terminate the string.
+ * This function will strip all trailing whitespace and
+ * NUL terminate the string.
  *
- * Return value:
- * 	new length of string
  **/
-static int strip_and_pad_whitespace(int i, char *buf)
+static void strip_whitespace(int i, char *buf)
 {
+	if (i < 1)
+		return;
+	i--;
 	while (i && buf[i] == ' ')
 		i--;
-	buf[i+1] = ' ';
-	buf[i+2] = '\0';
-	return i + 2;
+	buf[i+1] = '\0';
 }
 
 /**
@@ -1547,19 +1546,21 @@ static int strip_and_pad_whitespace(int i, char *buf)
 static void ipr_log_vpd_compact(char *prefix, struct ipr_hostrcb *hostrcb,
 				struct ipr_vpd *vpd)
 {
-	char buffer[IPR_VENDOR_ID_LEN + IPR_PROD_ID_LEN + IPR_SERIAL_NUM_LEN + 3];
-	int i = 0;
+	char vendor_id[IPR_VENDOR_ID_LEN + 1];
+	char product_id[IPR_PROD_ID_LEN + 1];
+	char sn[IPR_SERIAL_NUM_LEN + 1];
 
-	memcpy(buffer, vpd->vpids.vendor_id, IPR_VENDOR_ID_LEN);
-	i = strip_and_pad_whitespace(IPR_VENDOR_ID_LEN - 1, buffer);
+	memcpy(vendor_id, vpd->vpids.vendor_id, IPR_VENDOR_ID_LEN);
+	strip_whitespace(IPR_VENDOR_ID_LEN, vendor_id);
 
-	memcpy(&buffer[i], vpd->vpids.product_id, IPR_PROD_ID_LEN);
-	i = strip_and_pad_whitespace(i + IPR_PROD_ID_LEN - 1, buffer);
+	memcpy(product_id, vpd->vpids.product_id, IPR_PROD_ID_LEN);
+	strip_whitespace(IPR_PROD_ID_LEN, product_id);
 
-	memcpy(&buffer[i], vpd->sn, IPR_SERIAL_NUM_LEN);
-	buffer[IPR_SERIAL_NUM_LEN + i] = '\0';
+	memcpy(sn, vpd->sn, IPR_SERIAL_NUM_LEN);
+	strip_whitespace(IPR_SERIAL_NUM_LEN, sn);
 
-	ipr_hcam_err(hostrcb, "%s VPID/SN: %s\n", prefix, buffer);
+	ipr_hcam_err(hostrcb, "%s VPID/SN: %s %s %s\n", prefix,
+		     vendor_id, product_id, sn);
 }
 
 /**
-- 
2.39.1