[Linux Kernel Bug] WARNING: ODEBUG bug in free_netdev

[Sam Sun]

Dear developers and maintainers,

We encountered a kernel warning while using our modified syzkaller.
The bug has been reproduced on the latest kernel
commit(9b332cece987ee1790b2ed4c989e28162fa47860). The kernel crash log is
listed below.

cdc_ncm 2-1:1.0 usb5: unregister 'cdc_ncm' usb-dummy_hcd.1-1, CDC NCM (NO ZLP)
------------[ cut here ]------------
ODEBUG: free active (active state 0) object: ff1100004c40d280 object
type: work_struct hint: usbnet_deferred_kevent+0x0/0xea0
drivers/net/usb/usbnet.c:1439
WARNING: CPU: 0 PID: 975 at lib/debugobjects.c:612
debug_print_object+0x1a2/0x2b0 lib/debugobjects.c:612
Modules linked in:
CPU: 0 UID: 0 PID: 975 Comm: kworker/0:2 Not tainted
6.17.0-rc5-00018-g9dd1835ecda5 #8 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Workqueue: usb_hub_wq hub_event
RIP: 0010:debug_print_object+0x1a2/0x2b0 lib/debugobjects.c:612
Code: fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 54 41 56 48 8b 14
dd e0 2b f6 8b 4c 89 e6 48 c7 c7 60 20 f6 8b e8 2f 10 9b fc 90 <0f> 0b
90 90 58 83 05 d6 da ac 0b 01 48 83 c4 18 5b 5d 41 5c 41 5d
RSP: 0018:ffa0000004d1f458 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff81795e09
RDX: ff1100001cbd0000 RSI: ffffffff81795e16 RDI: 0000000000000001
RBP: 0000000000000001 R08: 0000000000000001 R09: ffe21c00056c4841
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8bf62700
R13: ffffffff8b8c1c20 R14: ffffffff8715d610 R15: ffa0000004d1f548
FS: 0000000000000000(0000) GS:ff11000097ada000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9983176020 CR3: 0000000046572000 CR4: 0000000000753ef0
PKRU: 55555554
Call Trace:
<TASK>
__debug_check_no_obj_freed lib/debugobjects.c:1099 [inline]
debug_check_no_obj_freed+0x3ec/0x520 lib/debugobjects.c:1129
slab_free_hook mm/slub.c:2353 [inline]
slab_free mm/slub.c:4695 [inline]
kfree+0x2b1/0x4e0 mm/slub.c:4894
device_release+0xa6/0x240 drivers/base/core.c:2565
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x1af/0x4c0 lib/kobject.c:737
put_device+0x1f/0x30 drivers/base/core.c:3797
free_netdev+0x61b/0x900 net/core/dev.c:12002
usbnet_disconnect+0x25c/0x510 drivers/net/usb/usbnet.c:1673
usb_unbind_interface+0x1e5/0x9c0 drivers/usb/core/driver.c:458
device_remove drivers/base/dd.c:571 [inline]
device_remove+0x122/0x170 drivers/base/dd.c:563
__device_release_driver drivers/base/dd.c:1274 [inline]
device_release_driver_internal+0x43e/0x610 drivers/base/dd.c:1297
bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
device_del+0x396/0x9d0 drivers/base/core.c:3878
usb_disable_device+0x359/0x7b0 drivers/usb/core/message.c:1418
usb_disconnect+0x2df/0x9e0 drivers/usb/core/hub.c:2344
hub_port_connect drivers/usb/core/hub.c:5406 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5706 [inline]
port_event drivers/usb/core/hub.c:5870 [inline]
hub_event+0x1e6d/0x4e60 drivers/usb/core/hub.c:5952
process_one_work+0x98f/0x1b60 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x67e/0xe90 kernel/workqueue.c:3400
kthread+0x3cd/0x780 kernel/kthread.c:463
ret_from_fork+0x5d7/0x6f0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Though syzbot reported similar bug
(https://syzkaller.appspot.com/bug?extid=8bfd7bcc98f7300afb84), we
have successfully reproduced the bug with the following C program:

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <nftables/libnftables.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#include <linux/usb/ch9.h>

#ifndef __NR_bpf
#define __NR_bpf 321
#endif

static unsigned long long procid;

static void sleep_ms(uint64_t ms)
{
usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts))
exit(1);
return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

#define TCP_CONNECTIONS 8
#define UDP_CONNECTIONS 8
#define BASE_PORT 30000

static bool write_file(const char* file, const char* what, ...)
{
char buf[1024];
va_list args;
va_start(args, what);
vsnprintf(buf, sizeof(buf), what, args);
va_end(args);
buf[sizeof(buf) - 1] = 0;
int len = strlen(buf);
int fd = open(file, O_WRONLY | O_CLOEXEC);
if (fd == -1)
return false;
if (write(fd, buf, len) != len) {
int err = errno;
close(fd);
errno = err;
return false;
}
close(fd);
return true;
}

static int runcmdline(char* cmdline)
{
int ret = system(cmdline);
if (ret) {
}
return ret;
}

#define MAX_FDS 30

#define USB_MAX_IFACE_NUM 4
#define USB_MAX_EP_NUM 32
#define USB_MAX_FDS 6

struct usb_endpoint_index {
struct usb_endpoint_descriptor desc;
int handle;
};

struct usb_iface_index {
struct usb_interface_descriptor* iface;
uint8_t bInterfaceNumber;
uint8_t bAlternateSetting;
uint8_t bInterfaceClass;
struct usb_endpoint_index eps[USB_MAX_EP_NUM];
int eps_num;
};

struct usb_device_index {
struct usb_device_descriptor* dev;
struct usb_config_descriptor* config;
uint8_t bDeviceClass;
uint8_t bMaxPower;
int config_length;
struct usb_iface_index ifaces[USB_MAX_IFACE_NUM];
int ifaces_num;
int iface_cur;
};

struct usb_info {
int fd;
struct usb_device_index index;
};

static struct usb_info usb_devices[USB_MAX_FDS];

static struct usb_device_index* lookup_usb_index(int fd)
{
for (int i = 0; i < USB_MAX_FDS; i++) {
if (__atomic_load_n(&usb_devices[i].fd, __ATOMIC_ACQUIRE) == fd)
return &usb_devices[i].index;
}
return NULL;
}

static int usb_devices_num;

static bool parse_usb_descriptor(const char* buffer, size_t length,
struct usb_device_index* index)
{
if (length < sizeof(*index->dev) + sizeof(*index->config))
return false;
memset(index, 0, sizeof(*index));
index->dev = (struct usb_device_descriptor*)buffer;
index->config = (struct usb_config_descriptor*)(buffer + sizeof(*index->dev));
index->bDeviceClass = index->dev->bDeviceClass;
index->bMaxPower = index->config->bMaxPower;
index->config_length = length - sizeof(*index->dev);
index->iface_cur = -1;
size_t offset = 0;
while (true) {
if (offset + 1 >= length)
break;
uint8_t desc_length = buffer[offset];
uint8_t desc_type = buffer[offset + 1];
if (desc_length <= 2)
break;
if (offset + desc_length > length)
break;
if (desc_type == USB_DT_INTERFACE &&
index->ifaces_num < USB_MAX_IFACE_NUM) {
struct usb_interface_descriptor* iface =
(struct usb_interface_descriptor*)(buffer + offset);
index->ifaces[index->ifaces_num].iface = iface;
index->ifaces[index->ifaces_num].bInterfaceNumber =
iface->bInterfaceNumber;
index->ifaces[index->ifaces_num].bAlternateSetting =
iface->bAlternateSetting;
index->ifaces[index->ifaces_num].bInterfaceClass = iface->bInterfaceClass;
index->ifaces_num++;
}
if (desc_type == USB_DT_ENDPOINT && index->ifaces_num > 0) {
struct usb_iface_index* iface = &index->ifaces[index->ifaces_num - 1];
if (iface->eps_num < USB_MAX_EP_NUM) {
memcpy(&iface->eps[iface->eps_num].desc, buffer + offset,
sizeof(iface->eps[iface->eps_num].desc));
iface->eps_num++;
}
}
offset += desc_length;
}
return true;
}

static struct usb_device_index* add_usb_index(int fd, const char* dev,
size_t dev_len)
{
int i = __atomic_fetch_add(&usb_devices_num, 1, __ATOMIC_RELAXED);
if (i >= USB_MAX_FDS)
return NULL;
if (!parse_usb_descriptor(dev, dev_len, &usb_devices[i].index))
return NULL;
__atomic_store_n(&usb_devices[i].fd, fd, __ATOMIC_RELEASE);
return &usb_devices[i].index;
}

struct vusb_connect_string_descriptor {
uint32_t len;
char* str;
} __attribute__((packed));

struct vusb_connect_descriptors {
uint32_t qual_len;
char* qual;
uint32_t bos_len;
char* bos;
uint32_t strs_len;
struct vusb_connect_string_descriptor strs[0];
} __attribute__((packed));

static const char default_string[] = {8, USB_DT_STRING, 's', 0, 'y', 0, 'z', 0};

static const char default_lang_id[] = {4, USB_DT_STRING, 0x09, 0x04};

static bool
lookup_connect_response_in(int fd, const struct vusb_connect_descriptors* descs,
const struct usb_ctrlrequest* ctrl,
struct usb_qualifier_descriptor* qual,
char** response_data, uint32_t* response_length)
{
struct usb_device_index* index = lookup_usb_index(fd);
uint8_t str_idx;
if (!index)
return false;
switch (ctrl->bRequestType & USB_TYPE_MASK) {
case USB_TYPE_STANDARD:
switch (ctrl->bRequest) {
case USB_REQ_GET_DESCRIPTOR:
switch (ctrl->wValue >> 8) {
case USB_DT_DEVICE:
*response_data = (char*)index->dev;
*response_length = sizeof(*index->dev);
return true;
case USB_DT_CONFIG:
*response_data = (char*)index->config;
*response_length = index->config_length;
return true;
case USB_DT_STRING:
str_idx = (uint8_t)ctrl->wValue;
if (descs && str_idx < descs->strs_len) {
*response_data = descs->strs[str_idx].str;
*response_length = descs->strs[str_idx].len;
return true;
}
if (str_idx == 0) {
*response_data = (char*)&default_lang_id[0];
*response_length = default_lang_id[0];
return true;
}
*response_data = (char*)&default_string[0];
*response_length = default_string[0];
return true;
case USB_DT_BOS:
*response_data = descs->bos;
*response_length = descs->bos_len;
return true;
case USB_DT_DEVICE_QUALIFIER:
if (!descs->qual) {
qual->bLength = sizeof(*qual);
qual->bDescriptorType = USB_DT_DEVICE_QUALIFIER;
qual->bcdUSB = index->dev->bcdUSB;
qual->bDeviceClass = index->dev->bDeviceClass;
qual->bDeviceSubClass = index->dev->bDeviceSubClass;
qual->bDeviceProtocol = index->dev->bDeviceProtocol;
qual->bMaxPacketSize0 = index->dev->bMaxPacketSize0;
qual->bNumConfigurations = index->dev->bNumConfigurations;
qual->bRESERVED = 0;
*response_data = (char*)qual;
*response_length = sizeof(*qual);
return true;
}
*response_data = descs->qual;
*response_length = descs->qual_len;
return true;
default:
break;
}
break;
default:
break;
}
break;
default:
break;
}
return false;
}

typedef bool (*lookup_connect_out_response_t)(
int fd, const struct vusb_connect_descriptors* descs,
const struct usb_ctrlrequest* ctrl, bool* done);

static bool lookup_connect_response_out_generic(
int fd, const struct vusb_connect_descriptors* descs,
const struct usb_ctrlrequest* ctrl, bool* done)
{
switch (ctrl->bRequestType & USB_TYPE_MASK) {
case USB_TYPE_STANDARD:
switch (ctrl->bRequest) {
case USB_REQ_SET_CONFIGURATION:
*done = true;
return true;
default:
break;
}
break;
}
return false;
}

struct vusb_descriptor {
uint8_t req_type;
uint8_t desc_type;
uint32_t len;
char data[0];
} __attribute__((packed));

struct vusb_descriptors {
uint32_t len;
struct vusb_descriptor* generic;
struct vusb_descriptor* descs[0];
} __attribute__((packed));

struct vusb_response {
uint8_t type;
uint8_t req;
uint32_t len;
char data[0];
} __attribute__((packed));

struct vusb_responses {
uint32_t len;
struct vusb_response* generic;
struct vusb_response* resps[0];
} __attribute__((packed));

static bool lookup_control_response(const struct vusb_descriptors* descs,
const struct vusb_responses* resps,
struct usb_ctrlrequest* ctrl,
char** response_data,
uint32_t* response_length)
{
int descs_num = 0;
int resps_num = 0;
if (descs)
descs_num = (descs->len - offsetof(struct vusb_descriptors, descs)) /
sizeof(descs->descs[0]);
if (resps)
resps_num = (resps->len - offsetof(struct vusb_responses, resps)) /
sizeof(resps->resps[0]);
uint8_t req = ctrl->bRequest;
uint8_t req_type = ctrl->bRequestType & USB_TYPE_MASK;
uint8_t desc_type = ctrl->wValue >> 8;
if (req == USB_REQ_GET_DESCRIPTOR) {
int i;
for (i = 0; i < descs_num; i++) {
struct vusb_descriptor* desc = descs->descs[i];
if (!desc)
continue;
if (desc->req_type == req_type && desc->desc_type == desc_type) {
*response_length = desc->len;
if (*response_length != 0)
*response_data = &desc->data[0];
else
*response_data = NULL;
return true;
}
}
if (descs && descs->generic) {
*response_data = &descs->generic->data[0];
*response_length = descs->generic->len;
return true;
}
} else {
int i;
for (i = 0; i < resps_num; i++) {
struct vusb_response* resp = resps->resps[i];
if (!resp)
continue;
if (resp->type == req_type && resp->req == req) {
*response_length = resp->len;
if (*response_length != 0)
*response_data = &resp->data[0];
else
*response_data = NULL;
return true;
}
}
if (resps && resps->generic) {
*response_data = &resps->generic->data[0];
*response_length = resps->generic->len;
return true;
}
}
return false;
}

#define UDC_NAME_LENGTH_MAX 128

struct usb_raw_init {
__u8 driver_name[UDC_NAME_LENGTH_MAX];
__u8 device_name[UDC_NAME_LENGTH_MAX];
__u8 speed;
};

enum usb_raw_event_type {
USB_RAW_EVENT_INVALID = 0,
USB_RAW_EVENT_CONNECT = 1,
USB_RAW_EVENT_CONTROL = 2,
};

struct usb_raw_event {
__u32 type;
__u32 length;
__u8 data[0];
};

struct usb_raw_ep_io {
__u16 ep;
__u16 flags;
__u32 length;
__u8 data[0];
};

#define USB_RAW_EPS_NUM_MAX 30
#define USB_RAW_EP_NAME_MAX 16
#define USB_RAW_EP_ADDR_ANY 0xff

struct usb_raw_ep_caps {
__u32 type_control : 1;
__u32 type_iso : 1;
__u32 type_bulk : 1;
__u32 type_int : 1;
__u32 dir_in : 1;
__u32 dir_out : 1;
};

struct usb_raw_ep_limits {
__u16 maxpacket_limit;
__u16 max_streams;
__u32 reserved;
};

struct usb_raw_ep_info {
__u8 name[USB_RAW_EP_NAME_MAX];
__u32 addr;
struct usb_raw_ep_caps caps;
struct usb_raw_ep_limits limits;
};

struct usb_raw_eps_info {
struct usb_raw_ep_info eps[USB_RAW_EPS_NUM_MAX];
};

#define USB_RAW_IOCTL_INIT _IOW('U', 0, struct usb_raw_init)
#define USB_RAW_IOCTL_RUN _IO('U', 1)
#define USB_RAW_IOCTL_EVENT_FETCH _IOR('U', 2, struct usb_raw_event)
#define USB_RAW_IOCTL_EP0_WRITE _IOW('U', 3, struct usb_raw_ep_io)
#define USB_RAW_IOCTL_EP0_READ _IOWR('U', 4, struct usb_raw_ep_io)
#define USB_RAW_IOCTL_EP_ENABLE _IOW('U', 5, struct usb_endpoint_descriptor)
#define USB_RAW_IOCTL_EP_DISABLE _IOW('U', 6, __u32)
#define USB_RAW_IOCTL_EP_WRITE _IOW('U', 7, struct usb_raw_ep_io)
#define USB_RAW_IOCTL_EP_READ _IOWR('U', 8, struct usb_raw_ep_io)
#define USB_RAW_IOCTL_CONFIGURE _IO('U', 9)
#define USB_RAW_IOCTL_VBUS_DRAW _IOW('U', 10, __u32)
#define USB_RAW_IOCTL_EPS_INFO _IOR('U', 11, struct usb_raw_eps_info)
#define USB_RAW_IOCTL_EP0_STALL _IO('U', 12)
#define USB_RAW_IOCTL_EP_SET_HALT _IOW('U', 13, __u32)
#define USB_RAW_IOCTL_EP_CLEAR_HALT _IOW('U', 14, __u32)
#define USB_RAW_IOCTL_EP_SET_WEDGE _IOW('U', 15, __u32)

static int usb_raw_open()
{
return open("/dev/raw-gadget", O_RDWR);
}

static int usb_raw_init(int fd, uint32_t speed, const char* driver,
const char* device)
{
struct usb_raw_init arg;
strncpy((char*)&arg.driver_name[0], driver, sizeof(arg.driver_name));
strncpy((char*)&arg.device_name[0], device, sizeof(arg.device_name));
arg.speed = speed;
return ioctl(fd, USB_RAW_IOCTL_INIT, &arg);
}

static int usb_raw_run(int fd)
{
return ioctl(fd, USB_RAW_IOCTL_RUN, 0);
}

static int usb_raw_configure(int fd)
{
return ioctl(fd, USB_RAW_IOCTL_CONFIGURE, 0);
}

static int usb_raw_vbus_draw(int fd, uint32_t power)
{
return ioctl(fd, USB_RAW_IOCTL_VBUS_DRAW, power);
}

static int usb_raw_ep0_write(int fd, struct usb_raw_ep_io* io)
{
return ioctl(fd, USB_RAW_IOCTL_EP0_WRITE, io);
}

static int usb_raw_ep0_read(int fd, struct usb_raw_ep_io* io)
{
return ioctl(fd, USB_RAW_IOCTL_EP0_READ, io);
}

static int usb_raw_event_fetch(int fd, struct usb_raw_event* event)
{
return ioctl(fd, USB_RAW_IOCTL_EVENT_FETCH, event);
}

static int usb_raw_ep_enable(int fd, struct usb_endpoint_descriptor* desc)
{
return ioctl(fd, USB_RAW_IOCTL_EP_ENABLE, desc);
}

static int usb_raw_ep_disable(int fd, int ep)
{
return ioctl(fd, USB_RAW_IOCTL_EP_DISABLE, ep);
}

static int usb_raw_ep0_stall(int fd)
{
return ioctl(fd, USB_RAW_IOCTL_EP0_STALL, 0);
}

static int lookup_interface(int fd, uint8_t bInterfaceNumber,
uint8_t bAlternateSetting)
{
struct usb_device_index* index = lookup_usb_index(fd);
if (!index)
return -1;
for (int i = 0; i < index->ifaces_num; i++) {
if (index->ifaces[i].bInterfaceNumber == bInterfaceNumber &&
index->ifaces[i].bAlternateSetting == bAlternateSetting)
return i;
}
return -1;
}

#define USB_MAX_PACKET_SIZE 4096

struct usb_raw_control_event {
struct usb_raw_event inner;
struct usb_ctrlrequest ctrl;
char data[USB_MAX_PACKET_SIZE];
};

struct usb_raw_ep_io_data {
struct usb_raw_ep_io inner;
char data[USB_MAX_PACKET_SIZE];
};

static void set_interface(int fd, int n)
{
struct usb_device_index* index = lookup_usb_index(fd);
if (!index)
return;
if (index->iface_cur >= 0 && index->iface_cur < index->ifaces_num) {
for (int ep = 0; ep < index->ifaces[index->iface_cur].eps_num; ep++) {
int rv = usb_raw_ep_disable(
fd, index->ifaces[index->iface_cur].eps[ep].handle);
if (rv < 0) {
} else {
}
}
}
if (n >= 0 && n < index->ifaces_num) {
for (int ep = 0; ep < index->ifaces[n].eps_num; ep++) {
int rv = usb_raw_ep_enable(fd, &index->ifaces[n].eps[ep].desc);
if (rv < 0) {
} else {
index->ifaces[n].eps[ep].handle = rv;
}
}
index->iface_cur = n;
}
}

static int configure_device(int fd)
{
struct usb_device_index* index = lookup_usb_index(fd);
if (!index)
return -1;
int rv = usb_raw_vbus_draw(fd, index->bMaxPower);
if (rv < 0) {
return rv;
}
rv = usb_raw_configure(fd);
if (rv < 0) {
return rv;
}
set_interface(fd, 0);
return 0;
}

static volatile long
syz_usb_connect_impl(uint64_t speed, uint64_t dev_len, const char* dev,
const struct vusb_connect_descriptors* descs,
lookup_connect_out_response_t lookup_connect_response_out)
{
if (!dev) {
return -1;
}
int fd = usb_raw_open();
if (fd < 0) {
return fd;
}
if (fd >= MAX_FDS) {
close(fd);
return -1;
}
struct usb_device_index* index = add_usb_index(fd, dev, dev_len);
if (!index) {
return -1;
}
char device[32];
sprintf(&device[0], "dummy_udc.%llu", procid);
int rv = usb_raw_init(fd, speed, "dummy_udc", &device[0]);
if (rv < 0) {
return rv;
}
rv = usb_raw_run(fd);
if (rv < 0) {
return rv;
}
bool done = false;
while (!done) {
struct usb_raw_control_event event;
event.inner.type = 0;
event.inner.length = sizeof(event.ctrl);
rv = usb_raw_event_fetch(fd, (struct usb_raw_event*)&event);
if (rv < 0) {
return rv;
}
if (event.inner.type != USB_RAW_EVENT_CONTROL)
continue;
char* response_data = NULL;
uint32_t response_length = 0;
struct usb_qualifier_descriptor qual;
if (event.ctrl.bRequestType & USB_DIR_IN) {
if (!lookup_connect_response_in(fd, descs, &event.ctrl, &qual,
&response_data, &response_length)) {
usb_raw_ep0_stall(fd);
continue;
}
} else {
if (!lookup_connect_response_out(fd, descs, &event.ctrl, &done)) {
usb_raw_ep0_stall(fd);
continue;
}
response_data = NULL;
response_length = event.ctrl.wLength;
}
if ((event.ctrl.bRequestType & USB_TYPE_MASK) == USB_TYPE_STANDARD &&
event.ctrl.bRequest == USB_REQ_SET_CONFIGURATION) {
rv = configure_device(fd);
if (rv < 0) {
return rv;
}
}
struct usb_raw_ep_io_data response;
response.inner.ep = 0;
response.inner.flags = 0;
if (response_length > sizeof(response.data))
response_length = 0;
if (event.ctrl.wLength < response_length)
response_length = event.ctrl.wLength;
response.inner.length = response_length;
if (response_data)
memcpy(&response.data[0], response_data, response_length);
else
memset(&response.data[0], 0, response_length);
if (event.ctrl.bRequestType & USB_DIR_IN) {
rv = usb_raw_ep0_write(fd, (struct usb_raw_ep_io*)&response);
} else {
rv = usb_raw_ep0_read(fd, (struct usb_raw_ep_io*)&response);
}
if (rv < 0) {
return rv;
}
}
sleep_ms(200);
return fd;
}

static volatile long syz_usb_connect(volatile long a0, volatile long a1,
volatile long a2, volatile long a3)
{
uint64_t speed = a0;
uint64_t dev_len = a1;
const char* dev = (const char*)a2;
const struct vusb_connect_descriptors* descs =
(const struct vusb_connect_descriptors*)a3;
return syz_usb_connect_impl(speed, dev_len, dev, descs,
&lookup_connect_response_out_generic);
}

static volatile long syz_usb_control_io(volatile long a0, volatile long a1,
volatile long a2)
{
int fd = a0;
const struct vusb_descriptors* descs = (const struct vusb_descriptors*)a1;
const struct vusb_responses* resps = (const struct vusb_responses*)a2;
struct usb_raw_control_event event;
event.inner.type = 0;
event.inner.length = USB_MAX_PACKET_SIZE;
int rv = usb_raw_event_fetch(fd, (struct usb_raw_event*)&event);
if (rv < 0) {
return rv;
}
if (event.inner.type != USB_RAW_EVENT_CONTROL) {
return -1;
}
char* response_data = NULL;
uint32_t response_length = 0;
if ((event.ctrl.bRequestType & USB_DIR_IN) && event.ctrl.wLength) {
if (!lookup_control_response(descs, resps, &event.ctrl, &response_data,
&response_length)) {
usb_raw_ep0_stall(fd);
return -1;
}
} else {
if ((event.ctrl.bRequestType & USB_TYPE_MASK) == USB_TYPE_STANDARD ||
event.ctrl.bRequest == USB_REQ_SET_INTERFACE) {
int iface_num = event.ctrl.wIndex;
int alt_set = event.ctrl.wValue;
int iface_index = lookup_interface(fd, iface_num, alt_set);
if (iface_index < 0) {
} else {
set_interface(fd, iface_index);
}
}
response_length = event.ctrl.wLength;
}
struct usb_raw_ep_io_data response;
response.inner.ep = 0;
response.inner.flags = 0;
if (response_length > sizeof(response.data))
response_length = 0;
if (event.ctrl.wLength < response_length)
response_length = event.ctrl.wLength;
if ((event.ctrl.bRequestType & USB_DIR_IN) && !event.ctrl.wLength) {
response_length = USB_MAX_PACKET_SIZE;
}
response.inner.length = response_length;
if (response_data)
memcpy(&response.data[0], response_data, response_length);
else
memset(&response.data[0], 0, response_length);
if ((event.ctrl.bRequestType & USB_DIR_IN) && event.ctrl.wLength) {
rv = usb_raw_ep0_write(fd, (struct usb_raw_ep_io*)&response);
} else {
rv = usb_raw_ep0_read(fd, (struct usb_raw_ep_io*)&response);
}
if (rv < 0) {
return rv;
}
sleep_ms(200);
return 0;
}

static void kill_and_wait(int pid, int* status)
{
kill(-pid, SIGKILL);
kill(pid, SIGKILL);
for (int i = 0; i < 100; i++) {
if (waitpid(-1, status, WNOHANG | __WALL) == pid)
return;
usleep(1000);
}
DIR* dir = opendir("/sys/fs/fuse/connections");
if (dir) {
for (;;) {
struct dirent* ent = readdir(dir);
if (!ent)
break;
if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
continue;
char abort[300];
snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
ent->d_name);
int fd = open(abort, O_WRONLY);
if (fd == -1) {
continue;
}
if (write(fd, abort, 1) < 0) {
}
close(fd);
}
closedir(dir);
} else {
}
while (waitpid(-1, status, __WALL) != pid) {
}
}

static void setup_test()
{
prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
setpgrp();
write_file("/proc/self/oom_score_adj", "1000");
}

static void setup_sysctl()
{
int cad_pid = fork();
if (cad_pid < 0)
exit(1);
if (cad_pid == 0) {
for (;;)
sleep(100);
}
char tmppid[32];
snprintf(tmppid, sizeof(tmppid), "%d", cad_pid);
struct {
const char* name;
const char* data;
} files[] = {
{"/sys/kernel/debug/x86/nmi_longest_ns", "10000000000"},
{"/proc/sys/kernel/hung_task_check_interval_secs", "20"},
{"/proc/sys/net/core/bpf_jit_kallsyms", "1"},
{"/proc/sys/net/core/bpf_jit_harden", "0"},
{"/proc/sys/kernel/kptr_restrict", "0"},
{"/proc/sys/kernel/softlockup_all_cpu_backtrace", "1"},
{"/proc/sys/fs/mount-max", "100"},
{"/proc/sys/vm/oom_dump_tasks", "0"},
{"/proc/sys/debug/exception-trace", "0"},
{"/proc/sys/kernel/printk", "7 4 1 3"},
{"/proc/sys/kernel/keys/gc_delay", "1"},
{"/proc/sys/vm/oom_kill_allocating_task", "1"},
{"/proc/sys/kernel/ctrl-alt-del", "0"},
{"/proc/sys/kernel/cad_pid", tmppid},
};
for (size_t i = 0; i < sizeof(files) / sizeof(files[0]); i++) {
if (!write_file(files[i].name, files[i].data)) {
}
}
kill(cad_pid, SIGKILL);
while (waitpid(cad_pid, NULL, 0) != cad_pid)
;
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void)
{
int iter = 0;
for (;; iter++) {
int pid = fork();
if (pid < 0)
exit(1);
if (pid == 0) {
setup_test();
execute_one();
exit(0);
}
int status = 0;
uint64_t start = current_time_ms();
for (;;) {
sleep_ms(10);
if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
break;
if (current_time_ms() - start < 5000)
continue;
kill_and_wait(pid, &status);
break;
}
}
}

uint64_t r[1] = {0xffffffffffffffff};

void execute_one(void)
{
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {
}
*(uint8_t*)0x20000480 = 0x12;
*(uint8_t*)0x20000481 = 1;
*(uint16_t*)0x20000482 = 0;
*(uint8_t*)0x20000484 = 2;
*(uint8_t*)0x20000485 = 0;
*(uint8_t*)0x20000486 = 0;
*(uint8_t*)0x20000487 = 0x40;
*(uint16_t*)0x20000488 = 0x525;
*(uint16_t*)0x2000048a = 0xa4a1;
*(uint16_t*)0x2000048c = 0x40;
*(uint8_t*)0x2000048e = 1;
*(uint8_t*)0x2000048f = 2;
*(uint8_t*)0x20000490 = 3;
*(uint8_t*)0x20000491 = 1;
*(uint8_t*)0x20000492 = 9;
*(uint8_t*)0x20000493 = 2;
*(uint16_t*)0x20000494 = 0x5c;
*(uint8_t*)0x20000496 = 2;
*(uint8_t*)0x20000497 = 1;
*(uint8_t*)0x20000498 = 0;
*(uint8_t*)0x20000499 = 0;
*(uint8_t*)0x2000049a = 0;
*(uint8_t*)0x2000049b = 9;
*(uint8_t*)0x2000049c = 4;
*(uint8_t*)0x2000049d = 0;
*(uint8_t*)0x2000049e = 0;
*(uint8_t*)0x2000049f = 1;
*(uint8_t*)0x200004a0 = 2;
*(uint8_t*)0x200004a1 = 0xd;
*(uint8_t*)0x200004a2 = 0;
*(uint8_t*)0x200004a3 = 0;
*(uint8_t*)0x200004a4 = 5;
*(uint8_t*)0x200004a5 = 0x24;
*(uint8_t*)0x200004a6 = 6;
*(uint8_t*)0x200004a7 = 0;
*(uint8_t*)0x200004a8 = 1;
*(uint8_t*)0x200004a9 = 5;
*(uint8_t*)0x200004aa = 0x24;
*(uint8_t*)0x200004ab = 0;
*(uint16_t*)0x200004ac = 0;
*(uint8_t*)0x200004ae = 0xd;
*(uint8_t*)0x200004af = 0x24;
*(uint8_t*)0x200004b0 = 0xf;
*(uint8_t*)0x200004b1 = 1;
*(uint32_t*)0x200004b2 = 0;
*(uint16_t*)0x200004b6 = 2;
*(uint16_t*)0x200004b8 = 0;
*(uint8_t*)0x200004ba = 0;
*(uint8_t*)0x200004bb = 6;
*(uint8_t*)0x200004bc = 0x24;
*(uint8_t*)0x200004bd = 0x1a;
*(uint16_t*)0x200004be = 0;
*(uint8_t*)0x200004c0 = 0;
*(uint8_t*)0x200004c1 = 9;
*(uint8_t*)0x200004c2 = 5;
*(uint8_t*)0x200004c3 = 0x81;
*(uint8_t*)0x200004c4 = 3;
*(uint16_t*)0x200004c5 = 0x200;
*(uint8_t*)0x200004c7 = 0;
*(uint8_t*)0x200004c8 = 0;
*(uint8_t*)0x200004c9 = 0;
*(uint8_t*)0x200004ca = 9;
*(uint8_t*)0x200004cb = 4;
*(uint8_t*)0x200004cc = 1;
*(uint8_t*)0x200004cd = 0;
*(uint8_t*)0x200004ce = 0;
*(uint8_t*)0x200004cf = 2;
*(uint8_t*)0x200004d0 = 0xd;
*(uint8_t*)0x200004d1 = 0;
*(uint8_t*)0x200004d2 = 0;
*(uint8_t*)0x200004d3 = 9;
*(uint8_t*)0x200004d4 = 4;
*(uint8_t*)0x200004d5 = 1;
*(uint8_t*)0x200004d6 = 1;
*(uint8_t*)0x200004d7 = 2;
*(uint8_t*)0x200004d8 = 2;
*(uint8_t*)0x200004d9 = 0xd;
*(uint8_t*)0x200004da = 0;
*(uint8_t*)0x200004db = 0;
*(uint8_t*)0x200004dc = 9;
*(uint8_t*)0x200004dd = 5;
*(uint8_t*)0x200004de = 0x82;
*(uint8_t*)0x200004df = 2;
*(uint16_t*)0x200004e0 = 0x200;
*(uint8_t*)0x200004e2 = 0;
*(uint8_t*)0x200004e3 = 0;
*(uint8_t*)0x200004e4 = 0;
*(uint8_t*)0x200004e5 = 9;
*(uint8_t*)0x200004e6 = 5;
*(uint8_t*)0x200004e7 = 3;
*(uint8_t*)0x200004e8 = 2;
*(uint16_t*)0x200004e9 = 0x200;
*(uint8_t*)0x200004eb = 0;
*(uint8_t*)0x200004ec = 0;
*(uint8_t*)0x200004ed = 0;
res = -1;
res = syz_usb_connect(/*speed=*/0, /*dev_len=*/0x6e, /*dev=*/0x20000480,
/*conn_descs=*/0);
if (res != -1)
r[0] = res;
syz_usb_control_io(/*fd=*/r[0], /*descs=*/0, /*resps=*/0);
*(uint32_t*)0x20000540 = 0x101;
*(uint32_t*)0x20000544 = 0xf3ee;
*(uint32_t*)0x20000548 = 0xfffff8a7;
*(uint32_t*)0x2000054c = 0x10001;
*(uint32_t*)0x20000550 = 0xc;
syscall(__NR_setsockopt, /*fd=*/-1, /*level=*/6, /*optname=*/0x1d,
/*optval=*/0x20000540ul, /*optlen=*/0x14ul);
memcpy((void*)0x20000540, "\x03\x00\x00\x00\x04\x00\x00\x00\x04\x00\x00\x00",
12);
syscall(__NR_bpf, /*cmd=*/0ul, /*arg=*/0x20000540ul, /*size=*/0x48ul);
syscall(__NR_bpf, /*cmd=*/0ul, /*arg=*/0x20000540ul, /*size=*/0x48ul);
syz_usb_control_io(/*fd=*/r[0], /*descs=*/0, /*resps=*/0);
*(uint32_t*)0x20000340 = 0x44;
*(uint64_t*)0x20000344 = 0;
*(uint64_t*)0x2000034c = 0;
*(uint64_t*)0x20000354 = 0;
*(uint64_t*)0x2000035c = 0x20000200;
*(uint8_t*)0x20000200 = 0x20;
*(uint8_t*)0x20000201 = 0x80;
*(uint32_t*)0x20000202 = 0x1c;
*(uint16_t*)0x20000206 = 0x10;
*(uint16_t*)0x20000208 = 0x10;
*(uint32_t*)0x2000020a = 0x10;
*(uint16_t*)0x2000020e = 0x10;
*(uint16_t*)0x20000210 = 0x10;
*(uint16_t*)0x20000212 = 0x10;
*(uint16_t*)0x20000214 = 0x10;
*(uint32_t*)0x20000216 = 0x10;
*(uint16_t*)0x2000021a = 0x10;
*(uint16_t*)0x2000021c = 0x10;
*(uint16_t*)0x2000021e = 0x10;
*(uint16_t*)0x20000220 = 0x10;
*(uint64_t*)0x20000364 = 0;
*(uint64_t*)0x2000036c = 0;
*(uint64_t*)0x20000374 = 0;
*(uint64_t*)0x2000037c = 0;
syz_usb_control_io(/*fd=*/r[0], /*descs=*/0, /*resps=*/0x20000340);
syz_usb_control_io(/*fd=*/r[0], /*descs=*/0, /*resps=*/0);
*(uint32_t*)0x20000080 = 0x14;
*(uint64_t*)0x20000084 = 0;
*(uint64_t*)0x2000008c = 0x20000040;
*(uint8_t*)0x20000040 = 0;
*(uint8_t*)0x20000041 = 3;
*(uint32_t*)0x20000042 = 0x1a;
*(uint8_t*)0x20000046 = 0x1a;
*(uint8_t*)0x20000047 = 3;
*(uint64_t*)0x20000048 = htobe64(0x3400320034003200);
*(uint64_t*)0x20000050 = htobe64(0x3400320034003200);
*(uint64_t*)0x20000058 = htobe64(0x3400320034003200);
syz_usb_control_io(/*fd=*/r[0], /*descs=*/0x20000080, /*resps=*/0);
}
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul,
/*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
setup_sysctl();
const char* reason;
(void)reason;
for (procid = 0; procid < 6; procid++) {
if (fork() == 0) {
loop();
}
}
sleep(1000000);
return 0;
}

The kernel config is attached to this email. If you have any
questions, please contact us.

Best Regards,
Yue

[Lizhi Xu]

The root cause of this issue are:
1. When probing the usbnet device, executing usbnet_link_change(dev, 0, 0);
places the kevent in the waitqueue. However, the kevent has not yet been
scheduled when the usbnet device is unregistered. Therefore, executing
free_netdev() results in the "free active object (kevent)" error reported
here.

2. Another factor is that when calling usbnet_disconnect()->unregister_netdev(),
if the usbnet device is up, ndo_stop() is executed to cancel the kevent.
However, because the device is not up, ndo_stop() is not executed.

The solution to this problem is to cancel the kevent before executing
free_netdev(), which also deletes the delay timer.

Reported-by: Sam Sun <samsun...@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=8bfd7bcc98f7300afb84
Signed-off-by: Lizhi Xu <lizh...@windriver.com>
---
drivers/net/usb/usbnet.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index bf01f2728531..f0294f0e6612 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1672,6 +1672,9 @@ void usbnet_disconnect (struct usb_interface *intf)
usb_free_urb(dev->interrupt);
kfree(dev->padding_pkt);

+ cancel_work_sync(&dev->kevent);
+ timer_delete_sync(&dev->delay);
+
free_netdev(net);
}
EXPORT_SYMBOL_GPL(usbnet_disconnect);
--
2.43.0

[Lizhi Xu]

The root cause of this issue are:
1. When probing the usbnet device, executing usbnet_link_change(dev, 0, 0);

put the kevent work in global workqueue. However, the kevent has not yet

been scheduled when the usbnet device is unregistered. Therefore, executing
free_netdev() results in the "free active object (kevent)" error reported
here.

2. Another factor is that when calling usbnet_disconnect()->unregister_netdev(),
if the usbnet device is up, ndo_stop() is executed to cancel the kevent.
However, because the device is not up, ndo_stop() is not executed.

The solution to this problem is to cancel the kevent before executing
free_netdev(), which also deletes the delay timer.

Reported-by: Sam Sun <samsun...@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=8bfd7bcc98f7300afb84
Signed-off-by: Lizhi Xu <lizh...@windriver.com>
---

V1 -> V2: update comments for typos

[Jakub Kicinski]

On Fri, 17 Oct 2025 17:05:41 +0800 Lizhi Xu wrote:
> The root cause of this issue are:
> 1. When probing the usbnet device, executing usbnet_link_change(dev, 0, 0);
> put the kevent work in global workqueue. However, the kevent has not yet
> been scheduled when the usbnet device is unregistered. Therefore, executing
> free_netdev() results in the "free active object (kevent)" error reported
> here.
>
> 2. Another factor is that when calling usbnet_disconnect()->unregister_netdev(),
> if the usbnet device is up, ndo_stop() is executed to cancel the kevent.
> However, because the device is not up, ndo_stop() is not executed.
>
> The solution to this problem is to cancel the kevent before executing
> free_netdev(), which also deletes the delay timer.

Please add a fixes tag, and repost.
Please don't send new versions in reply to previous / existing threads.
Please read at least the tl;dr of:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html
--
pw-bot: cr