usb: gadget: f_ncm: align net_device lifecycle with bind/unbind

Currently, the net_device is allocated in ncm_alloc_inst() and freed in ncm_free_inst(). This ties the network interface's lifetime to the configuration instance rather than the USB connection (bind/unbind). This decoupling causes issues when the USB gadget is disconnected where the underlying gadget device is removed. The net_device can outlive its parent, leading to dangling sysfs links and NULL pointer dereferences when accessing the freed gadget device. Problem 1: NULL pointer dereference on disconnect Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Call trace: __pi_strlen+0x14/0x150 rtnl_fill_ifinfo+0x6b4/0x708 rtmsg_ifinfo_build_skb+0xd8/0x13c rtmsg_ifinfo+0x50/0xa0 __dev_notify_flags+0x4c/0x1f0 dev_change_flags+0x54/0x70 do_setlink+0x390/0xebc rtnl_newlink+0x7d0/0xac8 rtnetlink_rcv_msg+0x27c/0x410 netlink_rcv_skb+0x134/0x150 rtnetlink_rcv+0x18/0x28 netlink_unicast+0x254/0x3f0 netlink_sendmsg+0x2e0/0x3d4 Problem 2: Dangling sysfs symlinks console:/ # ls -l /sys/class/net/ncm0 lrwxrwxrwx ... /sys/class/net/ncm0 -> /sys/devices/platform/.../gadget.0/net/ncm0 console:/ # ls -l /sys/devices/platform/.../gadget.0/net/ncm0 ls: .../gadget.0/net/ncm0: No such file or directory Move the net_device allocation to ncm_bind() and deallocation to ncm_unbind(). This ensures the network interface exists only when the gadget function is actually bound to a configuration. To support pre-bind configuration (e.g., setting interface name or MAC address via configfs), cache user-provided options in f_ncm_opts using the gether_opts structure. Apply these cached settings to the net_device upon creation in ncm_bind(). Preserve the use-after-free fix from commit 6334b8e455 ("usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error"). Check opts->net in ncm_set_alt() and ncm_disable() to ensure gether_disconnect() runs only if a connection was established. Fixes: 40d133d7f5 ("usb: gadget: f_ncm: convert to new function interface with backward compatibility") Cc: stable@kernel.org Signed-off-by: Kuen-Han Tsai <khtsai@google.com> Link: https://patch.msgid.link/20251230-ncm-refactor-v1-3-793e347bc7a7@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2026-03-31 01:04:05 -04:00 · 2025-12-30 18:13:16 +08:00
parent 0c0981126b
commit 56a512a9b4
2 changed files with 67 additions and 67 deletions
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -83,6 +83,11 @@ static inline struct f_ncm *func_to_ncm(struct usb_function *f)
 	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);
+}
+
 /*-------------------------------------------------------------------------*/

 /*
@@ -859,6 +864,7 @@ static int ncm_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
 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 */
@@ -881,12 +887,13 @@ static int ncm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 		if (alt > 1)
 			goto fail;

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

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

 		spin_lock(&ncm->lock);
@@ -1366,14 +1374,16 @@ static int ncm_unwrap_ntb(struct gether *port,
 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");

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

 	if (ncm->notify->enabled) {
 		usb_ep_disable(ncm->notify);
@@ -1433,39 +1443,44 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 {
 	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;
 	}

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

-	ncm_opts->bound = true;
-
-	ncm_string_defs[1].s = ncm->ethaddr;
+	/* 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;

 	us = usb_gstrings_attach(cdev, ncm_strings,
 				 ARRAY_SIZE(ncm_string_defs));
@@ -1563,6 +1578,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 		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,
@@ -1577,19 +1594,19 @@ static inline struct f_ncm_opts *to_f_ncm_opts(struct config_item *item)
 }

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

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

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

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

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

 static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
 					      char *page)
@@ -1655,34 +1672,27 @@ static void ncm_free_inst(struct usb_function_instance *f)
 	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 f_ncm_opts *opts;
+	struct usb_function_instance *ret;
 	struct usb_os_desc *descs[1];
 	char *names[1];
 	struct config_group *ncm_interf_group;

-	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
+	struct f_ncm_opts *opts __free(kfree) = 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);

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

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

 static void ncm_free(struct usb_function *f)
 {
-	struct f_ncm *ncm;
-	struct f_ncm_opts *opts;
+	struct f_ncm_opts *opts = func_to_ncm_opts(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);
+	scoped_guard(mutex, &opts->lock)
+		opts->refcnt--;
+	kfree(func_to_ncm(f));
 }

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

 	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);
@@ -1750,22 +1758,12 @@ static struct usb_function *ncm_alloc(struct usb_function_instance *fi)
 		return ERR_PTR(-ENOMEM);

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

 	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
@@ -15,11 +15,13 @@

 #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];