Revert "usb: legacy: ncm: Fix NPE in gncm_bind"

This reverts commit fde0634.

This commit is being reverted as part of a series-wide revert.

By deferring the net_device allocation to the bind() phase, a single
function instance will spawn multiple network devices if it is symlinked
to multiple USB configurations.

This causes regressions for userspace tools (like the postmarketOS DHCP
daemon) that rely on reading the interface name (e.g., "usb0") from
configfs. Currently, configfs returns the template "usb%d", causing the
userspace network setup to fail.

Crucially, because this patch breaks the 1:1 mapping between the
function instance and the network device, this naming issue cannot
simply be patched. Configfs only exposes a single 'ifname' attribute per
instance, making it impossible to accurately report the actual interface
name when multiple underlying network devices can exist for that single
instance.

All configurations tied to the same function instance are meant to share
a single network device. Revert this change to restore the 1:1 mapping
by allocating the network device at the instance level (alloc_inst).

Reported-by: David Heidelberg <david@ixit.cz>
Closes: https://lore.kernel.org/linux-usb/70b558ea-a12e-4170-9b8e-c951131249af@ixit.cz/
Fixes: 56a512a ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind")
Cc: stable <stable@kernel.org>
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20260309-f-ncm-revert-v2-2-ea2afbc7d9b2@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Kuen-Han Tsai

drivers/usb/gadget/legacy/ncm.c

@@ -15,10 +15,8 @@
 /* #define DEBUG */
 /* #define VERBOSE_DEBUG */
 
-#include <linux/hex.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/string.h>
 #include <linux/usb/composite.h>
 
 #include "u_ether.h"
@@ -131,23 +129,18 @@ static int gncm_bind(struct usb_composite_dev *cdev)
 	struct usb_gadget	*gadget = cdev->gadget;
 	struct f_ncm_opts	*ncm_opts;
 	int			status;
-	u8			mac[ETH_ALEN];
 
 	f_ncm_inst = usb_get_function_instance("ncm");
 	if (IS_ERR(f_ncm_inst))
 		return PTR_ERR(f_ncm_inst);
 
 	ncm_opts = container_of(f_ncm_inst, struct f_ncm_opts, func_inst);
 
-	ncm_opts->net_opts.qmult = qmult;
-	if (host_addr && mac_pton(host_addr, mac)) {
-		memcpy(&ncm_opts->net_opts.host_mac, mac, ETH_ALEN);
+	gether_set_qmult(ncm_opts->net, qmult);
+	if (!gether_set_host_addr(ncm_opts->net, host_addr))
 		pr_info("using host ethernet address: %s", host_addr);
-	}
-	if (dev_addr && mac_pton(dev_addr, mac)) {
-		memcpy(&ncm_opts->net_opts.dev_mac, mac, ETH_ALEN);
+	if (!gether_set_dev_addr(ncm_opts->net, dev_addr))
 		pr_info("using self ethernet address: %s", dev_addr);
-	}
 
 	/* Allocate string descriptor numbers ... note that string
 	 * contents can be overridden by the composite_dev glue.