Revert "usb: yurex: Replace snprintf() with the safer scnprintf() variant"

This reverts commit 86b20af.

This patch leads to passing 0 to simple_read_from_buffer()
as a fifth argument, turning the read method into a nop.
The change is fundamentally flawed, as it breaks the driver.

Signed-off-by: Oliver Neukum <[email protected]>
Cc: stable <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: oneukum

drivers/usb/misc/yurex.c

@@ -34,8 +34,6 @@
 #define YUREX_BUF_SIZE		8
 #define YUREX_WRITE_TIMEOUT	(HZ*2)
 
-#define MAX_S64_STRLEN 20 /* {-}922337203685477580{7,8} */
-
 /* table of devices that work with this driver */
 static struct usb_device_id yurex_table[] = {
 	{ USB_DEVICE(YUREX_VENDOR_ID, YUREX_PRODUCT_ID) },
@@ -403,7 +401,8 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
 {
 	struct usb_yurex *dev;
 	int len = 0;
-	char in_buffer[MAX_S64_STRLEN];
+	char in_buffer[20];
+	unsigned long flags;
 
 	dev = file->private_data;
 
@@ -413,16 +412,14 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
 		return -ENODEV;
 	}
 
-	if (WARN_ON_ONCE(dev->bbu > S64_MAX || dev->bbu < S64_MIN)) {
-		mutex_unlock(&dev->io_mutex);
-		return -EIO;
-	}
-
-	spin_lock_irq(&dev->lock);
-	scnprintf(in_buffer, MAX_S64_STRLEN, "%lld\n", dev->bbu);
-	spin_unlock_irq(&dev->lock);
+	spin_lock_irqsave(&dev->lock, flags);
+	len = snprintf(in_buffer, 20, "%lld\n", dev->bbu);
+	spin_unlock_irqrestore(&dev->lock, flags);
 	mutex_unlock(&dev->io_mutex);
 
+	if (WARN_ON_ONCE(len >= sizeof(in_buffer)))
+		return -EIO;
+
 	return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);
 }