[PATCH] USB: serial: digi_acceleport: fix write buffer corruption

[Johan Hovold <johan@kernel.org>]

The digi_write_inb_command() is supposed to wait for the write urb to
become available or return an error, but instead it updates the transfer
buffer and tries to resubmit the urb on timeout.

To make things worse, for commands like break control where no timeout
is used, the driver would corrupt the urb immediately due to a broken
jiffies comparison (on 32-bit machines this takes five minutes of uptime
to trigger due to INITIAL_JIFFIES).

Fix this by adding the missing return on timeout and waiting
indefinitely when no timeout has been specified as intended.

This issue was (sort of) flagged by Sashiko when reviewing an unrelated
change to the driver.

Link: https://sashiko.dev/#/patchset/20260610132232.356139-1-johan%40kernel.org?part=11
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/digi_acceleport.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/serial/digi_acceleport.c b/drivers/usb/serial/digi_acceleport.c
index 88c61030982a..fa5c3539f806 100644
--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -429,20 +429,22 @@ static int digi_write_inb_command(struct usb_serial_port *port,
 	int len;
 	struct digi_port *priv = usb_get_serial_port_data(port);
 	unsigned char *data = port->write_urb->transfer_buffer;
+	unsigned long expire;
 	unsigned long flags;
 
 	dev_dbg(&port->dev, "digi_write_inb_command: TOP: port=%d, count=%d\n",
 		priv->dp_port_num, count);
 
 	if (timeout)
-		timeout += jiffies;
-	else
-		timeout = ULONG_MAX;
+		expire = jiffies + timeout;
 
 	spin_lock_irqsave(&priv->dp_port_lock, flags);
 	while (count > 0 && ret == 0) {
-		while (priv->dp_write_urb_in_use &&
-		       time_before(jiffies, timeout)) {
+		while (priv->dp_write_urb_in_use) {
+			if (timeout && time_after(jiffies, expire)) {
+				ret = -ETIMEDOUT;
+				break;
+			}
 			cond_wait_interruptible_timeout_irqrestore(
 				&priv->write_wait, DIGI_RETRY_TIMEOUT,
 				&priv->dp_port_lock, flags);
@@ -451,6 +453,9 @@ static int digi_write_inb_command(struct usb_serial_port *port,
 			spin_lock_irqsave(&priv->dp_port_lock, flags);
 		}
 
+		if (ret)
+			break;
+
 		/* len must be a multiple of 4 and small enough to */
 		/* guarantee the write will send buffered data first, */
 		/* so commands are in order with data and not split */
-- 
2.53.0