usb: usbtmc: Fix erroneous get_stb ioctl error returns

wait_event_interruptible_timeout returns a long
The return was being assigned to an int causing an integer overflow when
the remaining jiffies > INT_MAX resulting in random error returns.

Use a long return value and convert to int ioctl return only on error.

When the return value of wait_event_interruptible_timeout was <= INT_MAX
the number of remaining jiffies was returned which has no meaning for the
user. Return 0 on success.

Reported-by: Michael Katzmann <vk2bea@gmail.com>
Fixes: dbf3e7f ("Implement an ioctl to support the USMTMC-USB488 READ_STATUS_BYTE operation.")
Cc: stable@vger.kernel.org
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250502070941.31819-2-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dpenkler

drivers/usb/class/usbtmc.c

@@ -482,6 +482,7 @@ static int usbtmc_get_stb(struct usbtmc_file_data *file_data, __u8 *stb)
 	u8 *buffer;
 	u8 tag;
 	int rv;
+	long wait_rv;
 
 	dev_dbg(dev, "Enter ioctl_read_stb iin_ep_present: %d\n",
 		data->iin_ep_present);
@@ -511,16 +512,17 @@ static int usbtmc_get_stb(struct usbtmc_file_data *file_data, __u8 *stb)
 	}
 
 	if (data->iin_ep_present) {
-		rv = wait_event_interruptible_timeout(
+		wait_rv = wait_event_interruptible_timeout(
 			data->waitq,
 			atomic_read(&data->iin_data_valid) != 0,
 			file_data->timeout);
-		if (rv < 0) {
-			dev_dbg(dev, "wait interrupted %d\n", rv);
+		if (wait_rv < 0) {
+			dev_dbg(dev, "wait interrupted %ld\n", wait_rv);
+			rv = wait_rv;
 			goto exit;
 		}
 
-		if (rv == 0) {
+		if (wait_rv == 0) {
 			dev_dbg(dev, "wait timed out\n");
 			rv = -ETIMEDOUT;
 			goto exit;
@@ -539,6 +541,8 @@ static int usbtmc_get_stb(struct usbtmc_file_data *file_data, __u8 *stb)
 
 	dev_dbg(dev, "stb:0x%02x received %d\n", (unsigned int)*stb, rv);
 
+	rv = 0;
+
  exit:
 	/* bump interrupt bTag */
 	data->iin_bTag += 1;