scsi: core: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the actual
output size, the succeeding calls may go beyond the given buffer limit.
Fix it by replacing with scnprintf().

Link: https://lore.kernel.org/r/20200315094241.9086-8-tiwai@suse.de
Cc: "James E . J . Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K . Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Reviewed-by: Bart van Assche <bvanassche@acm.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_sysfs.c

@@ -1045,14 +1045,14 @@ sdev_show_blacklist(struct device *dev, struct device_attribute *attr,
 			name = sdev_bflags_name[i];
 
 		if (name)
-			len += snprintf(buf + len, PAGE_SIZE - len,
-					"%s%s", len ? " " : "", name);
+			len += scnprintf(buf + len, PAGE_SIZE - len,
+					 "%s%s", len ? " " : "", name);
 		else
-			len += snprintf(buf + len, PAGE_SIZE - len,
-					"%sINVALID_BIT(%d)", len ? " " : "", i);
+			len += scnprintf(buf + len, PAGE_SIZE - len,
+					 "%sINVALID_BIT(%d)", len ? " " : "", i);
 	}
 	if (len)
-		len += snprintf(buf + len, PAGE_SIZE - len, "\n");
+		len += scnprintf(buf + len, PAGE_SIZE - len, "\n");
 	return len;
 }
 static DEVICE_ATTR(blacklist, S_IRUGO, sdev_show_blacklist, NULL);