[PATCH 6.6 032/105] usb: gadget: f_ncm: Refactor bind path to use __free()

Greg Kroah-Hartman
2025-10-21T19:53:51Z

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

[ Upstream commit 75a5b8d4ddd4eb6b16cb0b475d14ff4ae64295ef ]

After an bind/unbind cycle, the ncm->notify_req is left stale. If a
subsequent bind fails, the unified error label attempts to free this
stale request, leading to a NULL pointer dereference when accessing
ep->ops->free_request.

Refactor the error handling in the bind path to use the __free()
automatic cleanup mechanism.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
Call trace:
usb_ep_free_request+0x2c/0xec
ncm_bind+0x39c/0x3dc
usb_add_function+0xcc/0x1f0
configfs_composite_bind+0x468/0x588
gadget_bind_driver+0x104/0x270
really_probe+0x190/0x374
__driver_probe_device+0xa0/0x12c
driver_probe_device+0x3c/0x218
__device_attach_driver+0x14c/0x188
bus_for_each_drv+0x10c/0x168
__device_attach+0xfc/0x198
device_initial_probe+0x14/0x24
bus_probe_device+0x94/0x11c
device_add+0x268/0x48c
usb_add_gadget+0x198/0x28c
dwc3_gadget_init+0x700/0x858
__dwc3_set_mode+0x3cc/0x664
process_scheduled_works+0x1d8/0x488
worker_thread+0x244/0x334
kthread+0x114/0x1bc
ret_from_fork+0x10/0x20

Fixes: 9f6ce4240a2b ("usb: gadget: f_ncm.c added")
Cc: stable@kernel.org
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://lore.kernel.org/r/20250916-ready-v1-3-4997bf277548@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250916-ready-v1-3-4997bf277548@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/gadget/function/f_ncm.c | 78 +++++++++++++++---------------------
1 file changed, 33 insertions(+), 45 deletions(-)

--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -11,6 +11,7 @@
* Copyright (C) 2008 Nokia Corporation
*/

+#include <linux/cleanup.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/module.h>
@@ -19,6 +20,7 @@
#include <linux/crc32.h>

#include <linux/usb/cdc.h>
+#include <linux/usb/gadget.h>

#include "u_ether.h"
#include "u_ether_configfs.h"
@@ -1422,18 +1424,18 @@ static int ncm_bind(struct usb_configura
struct usb_ep *ep;
struct f_ncm_opts *ncm_opts;

+ struct usb_os_desc_table *os_desc_table __free(kfree) = 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) {
- f->os_desc_table = kzalloc(sizeof(*f->os_desc_table),
- GFP_KERNEL);
- if (!f->os_desc_table)
+ os_desc_table = kzalloc(sizeof(*os_desc_table), GFP_KERNEL);
+ if (!os_desc_table)
return -ENOMEM;
- f->os_desc_n = 1;
- f->os_desc_table[0].os_desc = &ncm_opts->ncm_os_desc;
}

mutex_lock(&ncm_opts->lock);
@@ -1443,16 +1445,15 @@ static int ncm_bind(struct usb_configura
mutex_unlock(&ncm_opts->lock);

if (status)
- goto fail;
+ return status;

ncm_opts->bound = true;

us = usb_gstrings_attach(cdev, ncm_strings,
ARRAY_SIZE(ncm_string_defs));
- if (IS_ERR(us)) {
- status = PTR_ERR(us);
- goto fail;
- }
+ if (IS_ERR(us))
+ return PTR_ERR(us);
+
ncm_control_intf.iInterface = us[STRING_CTRL_IDX].id;
ncm_data_nop_intf.iInterface = us[STRING_DATA_IDX].id;
ncm_data_intf.iInterface = us[STRING_DATA_IDX].id;
@@ -1462,55 +1463,47 @@ static int ncm_bind(struct usb_configura
/* allocate instance-specific interface IDs */
status = usb_interface_id(c, f);
if (status < 0)
- goto fail;
+ return status;
ncm->ctrl_id = status;
ncm_iad_desc.bFirstInterface = status;

ncm_control_intf.bInterfaceNumber = status;
ncm_union_desc.bMasterInterface0 = status;

- if (cdev->use_os_string)
- f->os_desc_table[0].if_id =
- ncm_iad_desc.bFirstInterface;
-
status = usb_interface_id(c, f);
if (status < 0)
- goto fail;
+ return status;
ncm->data_id = status;

ncm_data_nop_intf.bInterfaceNumber = status;
ncm_data_intf.bInterfaceNumber = status;
ncm_union_desc.bSlaveInterface0 = status;

- status = -ENODEV;
-
/* allocate instance-specific endpoints */
ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
ncm->port.in_ep = ep;

ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_out_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
ncm->port.out_ep = ep;

ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_notify_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
ncm->notify = ep;

- status = -ENOMEM;
-
/* allocate notification request and buffer */
- ncm->notify_req = usb_ep_alloc_request(ep, GFP_KERNEL);
- if (!ncm->notify_req)
- goto fail;
- ncm->notify_req->buf = kmalloc(NCM_STATUS_BYTECOUNT, GFP_KERNEL);
- if (!ncm->notify_req->buf)
- goto fail;
- ncm->notify_req->context = ncm;
- ncm->notify_req->complete = ncm_notify_complete;
+ request = usb_ep_alloc_request(ep, GFP_KERNEL);
+ if (!request)
+ return -ENOMEM;
+ request->buf = kmalloc(NCM_STATUS_BYTECOUNT, GFP_KERNEL);
+ if (!request->buf)
+ return -ENOMEM;
+ request->context = ncm;
+ request->complete = ncm_notify_complete;

/*
* support all relevant hardware speeds... we expect that when
@@ -1530,7 +1523,7 @@ static int ncm_bind(struct usb_configura
status = usb_assign_descriptors(f, ncm_fs_function, ncm_hs_function,
ncm_ss_function, ncm_ss_function);
if (status)
- goto fail;
+ return status;

/*
* NOTE: all that is done without knowing or caring about
@@ -1544,23 +1537,18 @@ static int ncm_bind(struct usb_configura
hrtimer_init(&ncm->task_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
ncm->task_timer.function = ncm_tx_timeout;

+ if (cdev->use_os_string) {
+ os_desc_table[0].os_desc = &ncm_opts->ncm_os_desc;
+ os_desc_table[0].if_id = ncm_iad_desc.bFirstInterface;
+ f->os_desc_table = no_free_ptr(os_desc_table);
+ f->os_desc_n = 1;
+ }
+ ncm->notify_req = no_free_ptr(request);
+
DBG(cdev, "CDC Network: IN/%s OUT/%s NOTIFY/%s\n",
ncm->port.in_ep->name, ncm->port.out_ep->name,
ncm->notify->name);
return 0;
-
-fail:
- kfree(f->os_desc_table);
- f->os_desc_n = 0;
-
- if (ncm->notify_req) {
- kfree(ncm->notify_req->buf);
- usb_ep_free_request(ncm->notify, ncm->notify_req);
- }
-
- ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);
-
- return status;
}

static inline struct f_ncm_opts *to_f_ncm_opts(struct config_item *item)