[PATCH v2 2/2] can: kvaser_usb: reject devices reporting zero max outstanding tx

[Joas Antonio dos Santos via B4 Relay <devnull+joasantonio108.gmail.com@kernel.org>]

From: Joas Antonio dos Santos <joasantonio108@gmail.com>

The number of tx contexts is taken from the max_outstanding_tx field of
the software info reply sent by the device.  The leaf driver uses the
value as is and the hydra driver only limits it to
KVASER_USB_MAX_TX_URBS, so a device can report zero.

dev->max_tx_urbs is then used as a divisor when a tx acknowledge is
received:

  kvaser_usb_leaf_tx_acknowledge()
	context = &priv->tx_contexts[tid % dev->max_tx_urbs];

  kvaser_usb_hydra_tx_acknowledge()
	context = &priv->tx_contexts[transid % dev->max_tx_urbs];

With max_tx_urbs == 0 a tx acknowledge sent by the device while the
interface is up is a division by zero in the URB completion handler on
architectures that trap on it.  On architectures that do not
trap, the index is not reduced at all and tx_contexts[], which was
allocated with zero elements, is accessed out of bounds.

A device that cannot accept any outstanding tx frame is not usable, so
fail the probe when it reports zero.

Found by LLM-assisted source review.

Fixes: 082d70b6142f ("can: kvaser_usb: Comply with firmware max tx URBs value")
Cc: stable@vger.kernel.org
Signed-off-by: Joas Antonio dos Santos <joasantonio108@gmail.com>
---
 drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c b/drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c
index d0a2a2a33c1c..a915e529290b 100644
--- a/drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c
+++ b/drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c
@@ -977,6 +977,12 @@ static int kvaser_usb_probe(struct usb_interface *intf,
 		goto free_devlink;
 	}
 
+	if (!dev->max_tx_urbs) {
+		dev_err(&intf->dev, "Invalid max outstanding tx (0)\n");
+		err = -ENODEV;
+		goto free_devlink;
+	}
+
 	if (ops->dev_get_software_details) {
 		err = ops->dev_get_software_details(dev);
 		if (err) {

-- 
2.43.0