net: usb: usbnet: restore usb%d name exception for local mac addresses

commit 8a7d12d674ac ("net: usb: usbnet: fix name regression") assumed
that local addresses always came from the kernel, but some devices hand
out local mac addresses so we ended up with point-to-point devices with
a mac set by the driver, renaming to eth%d when they used to be named
usb%d.

Userspace should not rely on device name, but for the sake of stability
restore the local mac address check portion of the naming exception:
point to point devices which either have no mac set by the driver or
have a local mac handed out by the driver will keep the usb%d name.

(some USB LTE modems are known to hand out a stable mac from the locally
administered range; that mac appears to be random (different for
mulitple devices) and can be reset with device-specific commands, so
while such devices would benefit from getting a OUI reserved, we have
to deal with these and might as well preserve the existing behavior
to avoid breaking fragile openwrt configurations and such on upgrade.)

Link: https://lkml.kernel.org/r/20241203130457.904325-1-asmadeus@codewreck.org
Fixes: 8a7d12d674ac ("net: usb: usbnet: fix name regression")
Cc: stable@vger.kernel.org
Tested-by: Ahmed Naseef <naseefkm@gmail.com>
Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
Acked-by: Oliver Neukum <oneukum@suse.com>
Link: https://patch.msgid.link/20250326-usbnet_rename-v2-1-57eb21fcff26@atmark-techno.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 44179f4e807fc350f3d5710f0bc5f42e6414fd6e..aeab2308b15008185336f717172b090739f4f9d0 100644 (file)
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -178,6 +178,17 @@ int usbnet_get_ethernet_addr(struct usbnet *dev, int iMACAddress)
 }
 EXPORT_SYMBOL_GPL(usbnet_get_ethernet_addr);
 
+static bool usbnet_needs_usb_name_format(struct usbnet *dev, struct net_device *net)
+{
+       /* Point to point devices which don't have a real MAC address
+        * (or report a fake local one) have historically used the usb%d
+        * naming. Preserve this..
+        */
+       return (dev->driver_info->flags & FLAG_POINTTOPOINT) != 0 &&
+               (is_zero_ether_addr(net->dev_addr) ||
+                is_local_ether_addr(net->dev_addr));
+}
+
 static void intr_complete (struct urb *urb)
 {
        struct usbnet   *dev = urb->context;
@@ -1762,13 +1773,11 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
                if (status < 0)
                        goto out1;
 
-               // heuristic:  "usb%d" for links we know are two-host,
-               // else "eth%d" when there's reasonable doubt.  userspace
-               // can rename the link if it knows better.
+               /* heuristic: rename to "eth%d" if we are not sure this link
+                * is two-host (these links keep "usb%d")
+                */
                if ((dev->driver_info->flags & FLAG_ETHER) != 0 &&
-                   ((dev->driver_info->flags & FLAG_POINTTOPOINT) == 0 ||
-                    /* somebody touched it*/
-                    !is_zero_ether_addr(net->dev_addr)))
+                   !usbnet_needs_usb_name_format(dev, net))
                        strscpy(net->name, "eth%d", sizeof(net->name));
                /* WLAN devices should always be named "wlan%d" */
                if ((dev->driver_info->flags & FLAG_WLAN) != 0)