netdev - [RFCv2] usbnet: assign unique random MAC

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Date: Mon, 20 Nov 2023 12:44:27 +0100
From: Oliver Neukum <oneukum@...e.com>
To: bjorn@...k.no,
	andrew@...n.ch,
	netdev@...r.kernel.org
Cc: Oliver Neukum <oneukum@...e.com>
Subject: [RFCv2] usbnet: assign unique random MAC

The old method had the bug of issuing the same
random MAC over and over even to every device.
This bug is as old as the driver.

This new method generates each device whose minidriver
does not provide its own MAC its own unique random
MAC.

Signed-off-by: Oliver Neukum <oneukum@...e.com>
---
 drivers/net/usb/usbnet.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 2d14b0d78541..0115ce11e78b 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -61,9 +61,6 @@
 
 /*-------------------------------------------------------------------------*/
 
-// randomly generated ethernet address
-static u8	node_id [ETH_ALEN];
-
 /* use ethtool to change the level for any given device */
 static int msg_level = -1;
 module_param (msg_level, int, 0);
@@ -1672,6 +1669,7 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 	struct usb_device		*xdev;
 	int				status;
 	const char			*name;
+	u8				initialaddr[ETH_ALEN];
 	struct usb_driver 	*driver = to_usb_driver(udev->dev.driver);
 
 	/* usbnet already took usb runtime pm, so have to enable the feature
@@ -1683,6 +1681,7 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 		pm_runtime_enable(&udev->dev);
 	}
 
+	eth_random_addr(initialaddr);
 	name = udev->dev.driver->name;
 	info = (const struct driver_info *) prod->driver_info;
 	if (!info) {
@@ -1731,7 +1730,7 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 
 	dev->net = net;
 	strscpy(net->name, "usb%d", sizeof(net->name));
-	eth_hw_addr_set(net, node_id);
+	eth_hw_addr_set(net, initialaddr);
 
 	/* rx and tx sides can use different message sizes;
 	 * bind() should set rx_urb_size in that case.
@@ -1805,8 +1804,13 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 		goto out4;
 	}
 
-	/* let userspace know we have a random address */
-	if (ether_addr_equal(net->dev_addr, node_id))
+	/* we assign a random MAC before we call bind
+	 * because we need to have the local assignment bit set
+	 * Before we mess around with temporary stuff we can
+	 * just as well generate a real random MAC
+	 * That means we need to set the flag if necessary
+	 */
+	if (ether_addr_equal(net->dev_addr, initialaddr))
 		net->addr_assign_type = NET_ADDR_RANDOM;
 
 	if ((dev->driver_info->flags & FLAG_WLAN) != 0)
@@ -2217,7 +2221,6 @@ static int __init usbnet_init(void)
 	BUILD_BUG_ON(
 		sizeof_field(struct sk_buff, cb) < sizeof(struct skb_data));
 
-	eth_random_addr(node_id);
 	return 0;
 }
 module_init(usbnet_init);
-- 
2.42.1