linux-kernel - [PATCH v2] net: usb: usbnet: restore usb%d name exception for local mac addresses

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Message-Id: <20250326-usbnet_rename-v2-1-57eb21fcff26@atmark-techno.com>
Date: Wed, 26 Mar 2025 17:32:36 +0900
From: Dominique Martinet <dominique.martinet@...ark-techno.com>
To: Oliver Neukum <oneukum@...e.com>, Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-usb@...r.kernel.org, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Ahmed Naseef <naseefkm@...il.com>, 
 Dominique Martinet <dominique.martinet@...ark-techno.com>
Subject: [PATCH v2] 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@...r.kernel.org
Tested-by: Ahmed Naseef <naseefkm@...il.com>
Signed-off-by: Dominique Martinet <dominique.martinet@...ark-techno.com>
---
Changes in v2:
- Added Cc stable as requested
- Fix block comment style (checkpatch warning)
- Added some more details about the local device handing out local macs
and openwrt, thank you for the reminder Ahmed.
(FWIW this commit has been in our downstream tree all this time and we've
had no obvious errors due to it)
- Link to v1: https://lore.kernel.org/r/20241203130457.904325-1-asmadeus@codewreck.org
---
 drivers/net/usb/usbnet.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 44179f4e807fc350f3d5710f0bc5f42e6414fd6e..aeab2308b15008185336f717172b090739f4f9d0 100644
--- 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)

---
base-commit: 0fed89a961ea851945d23cc35beb59d6e56c0964
change-id: 20250326-usbnet_rename-dff11e407634

Best regards,
-- 
Dominique Martinet <dominique.martinet@...ark-techno.com>