[PATCH 6.18 153/333] Revert "usb: gadget: f_ncm: align net_device lifecycle with bind/unbind"

Greg Kroah-Hartman
2026-03-17T17:16:03Z

From: Kuen-Han Tsai <khtsai@google.com>

commit 37893bc5de2460c543ec1aa8250c37a305234054 upstream.

This reverts commit 56a512a9b4107079f68701e7d55da8507eb963d9.

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: 56a512a9b410 ("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-v2-3-ea2afbc7d9b2@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/gadget/function/f_ncm.c | 128 ++++++++++++++++++------------------
drivers/usb/gadget/function/u_ncm.h | 4 -
2 files changed, 66 insertions(+), 66 deletions(-)

--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -83,11 +83,6 @@ static inline struct f_ncm *func_to_ncm(
return container_of(f, struct f_ncm, port.func);
}

-static inline struct f_ncm_opts *func_to_ncm_opts(struct usb_function *f)
-{
- return container_of(f->fi, struct f_ncm_opts, func_inst);
-}
-
/*-------------------------------------------------------------------------*/

/*
@@ -864,7 +859,6 @@ invalid:
static int ncm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
{
struct f_ncm *ncm = func_to_ncm(f);
- struct f_ncm_opts *opts = func_to_ncm_opts(f);
struct usb_composite_dev *cdev = f->config->cdev;

/* Control interface has only altsetting 0 */
@@ -887,13 +881,12 @@ static int ncm_set_alt(struct usb_functi
if (alt > 1)
goto fail;

- scoped_guard(mutex, &opts->lock)
- if (opts->net) {
- DBG(cdev, "reset ncm\n");
- opts->net = NULL;
- gether_disconnect(&ncm->port);
- ncm_reset_values(ncm);
- }
+ if (ncm->netdev) {
+ DBG(cdev, "reset ncm\n");
+ ncm->netdev = NULL;
+ gether_disconnect(&ncm->port);
+ ncm_reset_values(ncm);
+ }

/*
* CDC Network only sends data in non-default altsettings.
@@ -926,8 +919,7 @@ static int ncm_set_alt(struct usb_functi
net = gether_connect(&ncm->port);
if (IS_ERR(net))
return PTR_ERR(net);
- scoped_guard(mutex, &opts->lock)
- opts->net = net;
+ ncm->netdev = net;
}

spin_lock(&ncm->lock);
@@ -1374,16 +1366,14 @@ err:
static void ncm_disable(struct usb_function *f)
{
struct f_ncm *ncm = func_to_ncm(f);
- struct f_ncm_opts *opts = func_to_ncm_opts(f);
struct usb_composite_dev *cdev = f->config->cdev;

DBG(cdev, "ncm deactivated\n");

- scoped_guard(mutex, &opts->lock)
- if (opts->net) {
- opts->net = NULL;
- gether_disconnect(&ncm->port);
- }
+ if (ncm->netdev) {
+ ncm->netdev = NULL;
+ gether_disconnect(&ncm->port);
+ }

if (ncm->notify->enabled) {
usb_ep_disable(ncm->notify);
@@ -1443,44 +1433,39 @@ static int ncm_bind(struct usb_configura
{
struct usb_composite_dev *cdev = c->cdev;
struct f_ncm *ncm = func_to_ncm(f);
- struct f_ncm_opts *ncm_opts = func_to_ncm_opts(f);
struct usb_string *us;
int status = 0;
struct usb_ep *ep;
+ struct f_ncm_opts *ncm_opts;

struct usb_os_desc_table *os_desc_table __free(kfree) = NULL;
- struct net_device *netdev __free(free_gether_netdev) = NULL;
struct usb_request *request __free(free_usb_request) = NULL;

if (!can_support_ecm(cdev->gadget))
return -EINVAL;

+ ncm_opts = container_of(f->fi, struct f_ncm_opts, func_inst);
+
if (cdev->use_os_string) {
os_desc_table = kzalloc(sizeof(*os_desc_table), GFP_KERNEL);
if (!os_desc_table)
return -ENOMEM;
}

- netdev = gether_setup_default();
- if (IS_ERR(netdev))
- return -ENOMEM;
-
- scoped_guard(mutex, &ncm_opts->lock) {
- gether_apply_opts(netdev, &ncm_opts->net_opts);
- netdev->mtu = ncm_opts->max_segment_size - ETH_HLEN;
+ mutex_lock(&ncm_opts->lock);
+ gether_set_gadget(ncm_opts->net, cdev->gadget);
+ if (!ncm_opts->bound) {
+ ncm_opts->net->mtu = (ncm_opts->max_segment_size - ETH_HLEN);
+ status = gether_register_netdev(ncm_opts->net);
}
+ mutex_unlock(&ncm_opts->lock);

- gether_set_gadget(netdev, cdev->gadget);
- status = gether_register_netdev(netdev);
if (status)
return status;

- /* export host's Ethernet address in CDC format */
- status = gether_get_host_addr_cdc(netdev, ncm->ethaddr,
- sizeof(ncm->ethaddr));
- if (status < 12)
- return -EINVAL;
- ncm_string_defs[STRING_MAC_IDX].s = ncm->ethaddr;
+ ncm_opts->bound = true;
+
+ ncm_string_defs[1].s = ncm->ethaddr;

us = usb_gstrings_attach(cdev, ncm_strings,
ARRAY_SIZE(ncm_string_defs));
@@ -1578,8 +1563,6 @@ static int ncm_bind(struct usb_configura
f->os_desc_n = 1;
}
ncm->notify_req = no_free_ptr(request);
- ncm->netdev = no_free_ptr(netdev);
- ncm->port.ioport = netdev_priv(ncm->netdev);

DBG(cdev, "CDC Network: IN/%s OUT/%s NOTIFY/%s\n",
ncm->port.in_ep->name, ncm->port.out_ep->name,
@@ -1594,19 +1577,19 @@ static inline struct f_ncm_opts *to_f_nc
}

/* f_ncm_item_ops */
-USB_ETHER_OPTS_ITEM(ncm);
+USB_ETHERNET_CONFIGFS_ITEM(ncm);

/* f_ncm_opts_dev_addr */
-USB_ETHER_OPTS_ATTR_DEV_ADDR(ncm);
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_DEV_ADDR(ncm);

/* f_ncm_opts_host_addr */
-USB_ETHER_OPTS_ATTR_HOST_ADDR(ncm);
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_HOST_ADDR(ncm);

/* f_ncm_opts_qmult */
-USB_ETHER_OPTS_ATTR_QMULT(ncm);
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);

/* f_ncm_opts_ifname */
-USB_ETHER_OPTS_ATTR_IFNAME(ncm);
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);

static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
char *page)
@@ -1672,27 +1655,34 @@ static void ncm_free_inst(struct usb_fun
struct f_ncm_opts *opts;

opts = container_of(f, struct f_ncm_opts, func_inst);
+ if (opts->bound)
+ gether_cleanup(netdev_priv(opts->net));
+ else
+ free_netdev(opts->net);
kfree(opts->ncm_interf_group);
kfree(opts);
}

static struct usb_function_instance *ncm_alloc_inst(void)
{
- struct usb_function_instance *ret;
+ struct f_ncm_opts *opts;
struct usb_os_desc *descs[1];
char *names[1];
struct config_group *ncm_interf_group;

- struct f_ncm_opts *opts __free(kfree) = kzalloc(sizeof(*opts), GFP_KERNEL);
+ opts = kzalloc(sizeof(*opts), GFP_KERNEL);
if (!opts)
return ERR_PTR(-ENOMEM);
-
- opts->net = NULL;
opts->ncm_os_desc.ext_compat_id = opts->ncm_ext_compat_id;
- gether_setup_opts_default(&opts->net_opts, "usb");

mutex_init(&opts->lock);
opts->func_inst.free_func_inst = ncm_free_inst;
+ opts->net = gether_setup_default();
+ if (IS_ERR(opts->net)) {
+ struct net_device *net = opts->net;
+ kfree(opts);
+ return ERR_CAST(net);
+ }
opts->max_segment_size = ETH_FRAME_LEN;
INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);

@@ -1703,22 +1693,26 @@ static struct usb_function_instance *ncm
ncm_interf_group =
usb_os_desc_prepare_interf_dir(&opts->func_inst.group, 1, descs,
names, THIS_MODULE);
- if (IS_ERR(ncm_interf_group))
+ if (IS_ERR(ncm_interf_group)) {
+ ncm_free_inst(&opts->func_inst);
return ERR_CAST(ncm_interf_group);
+ }
opts->ncm_interf_group = ncm_interf_group;

- ret = &opts->func_inst;
- retain_and_null_ptr(opts);
- return ret;
+ return &opts->func_inst;
}

static void ncm_free(struct usb_function *f)
{
- struct f_ncm_opts *opts = func_to_ncm_opts(f);
+ struct f_ncm *ncm;
+ struct f_ncm_opts *opts;

- scoped_guard(mutex, &opts->lock)
- opts->refcnt--;
- kfree(func_to_ncm(f));
+ ncm = func_to_ncm(f);
+ opts = container_of(f->fi, struct f_ncm_opts, func_inst);
+ kfree(ncm);
+ mutex_lock(&opts->lock);
+ opts->refcnt--;
+ mutex_unlock(&opts->lock);
}

static void ncm_unbind(struct usb_configuration *c, struct usb_function *f)
@@ -1742,15 +1736,13 @@ static void ncm_unbind(struct usb_config

kfree(ncm->notify_req->buf);
usb_ep_free_request(ncm->notify, ncm->notify_req);
-
- ncm->port.ioport = NULL;
- gether_cleanup(netdev_priv(ncm->netdev));
}

static struct usb_function *ncm_alloc(struct usb_function_instance *fi)
{
struct f_ncm *ncm;
struct f_ncm_opts *opts;
+ int status;

/* allocate and initialize one new instance */
ncm = kzalloc(sizeof(*ncm), GFP_KERNEL);
@@ -1758,12 +1750,22 @@ static struct usb_function *ncm_alloc(st
return ERR_PTR(-ENOMEM);

opts = container_of(fi, struct f_ncm_opts, func_inst);
+ mutex_lock(&opts->lock);
+ opts->refcnt++;

- scoped_guard(mutex, &opts->lock)
- opts->refcnt++;
+ /* export host's Ethernet address in CDC format */
+ status = gether_get_host_addr_cdc(opts->net, ncm->ethaddr,
+ sizeof(ncm->ethaddr));
+ if (status < 12) { /* strlen("01234567890a") */
+ kfree(ncm);
+ mutex_unlock(&opts->lock);
+ return ERR_PTR(-EINVAL);
+ }

spin_lock_init(&ncm->lock);
ncm_reset_values(ncm);
+ ncm->port.ioport = netdev_priv(opts->net);
+ mutex_unlock(&opts->lock);
ncm->port.is_fixed = true;
ncm->port.supports_multi_frame = true;

--- a/drivers/usb/gadget/function/u_ncm.h
+++ b/drivers/usb/gadget/function/u_ncm.h
@@ -15,13 +15,11 @@

#include <linux/usb/composite.h>

-#include "u_ether.h"
-
struct f_ncm_opts {
struct usb_function_instance func_inst;
struct net_device *net;
+ bool bound;

- struct gether_opts net_opts;
struct config_group *ncm_interf_group;
struct usb_os_desc ncm_os_desc;
char ncm_ext_compat_id[16];