CVE-2023-53138

In the Linux kernel, the following vulnerability has been resolved:

net: caif: Fix use-after-free in cfusbl_device_notify()

syzbot reported use-after-free in cfusbl_device_notify() [1]. This

causes a stack trace like below:

BUG: KASAN: use-after-free in cfusbl_device_notify+0x7c9/0x870 net/caif/caif_usb.c:138

Read of size 8 at addr ffff88807ac4e6f0 by task kworker/u4:6/1214

CPU: 0 PID: 1214 Comm: kworker/u4:6 Not tainted 5.19.0-rc3-syzkaller-00146-g92f20ff72066 #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Workqueue: netns cleanup_net

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106

print_address_description.constprop.0.cold+0xeb/0x467 mm/kasan/report.c:313

print_report mm/kasan/report.c:429 [inline]

kasan_report.cold+0xf4/0x1c6 mm/kasan/report.c:491

cfusbl_device_notify+0x7c9/0x870 net/caif/caif_usb.c:138

notifier_call_chain+0xb5/0x200 kernel/notifier.c:87

call_netdevice_notifiers_info+0xb5/0x130 net/core/dev.c:1945

call_netdevice_notifiers_extack net/core/dev.c:1983 [inline]

call_netdevice_notifiers net/core/dev.c:1997 [inline]

netdev_wait_allrefs_any net/core/dev.c:10227 [inline]

netdev_run_todo+0xbc0/0x10f0 net/core/dev.c:10341

default_device_exit_batch+0x44e/0x590 net/core/dev.c:11334

ops_exit_list+0x125/0x170 net/core/net_namespace.c:167

cleanup_net+0x4ea/0xb00 net/core/net_namespace.c:594

process_one_work+0x996/0x1610 kernel/workqueue.c:2289

worker_thread+0x665/0x1080 kernel/workqueue.c:2436

kthread+0x2e9/0x3a0 kernel/kthread.c:376

ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302

</TASK>

When unregistering a net device, unregister_netdevice_many_notify()

sets the device's reg_state to NETREG_UNREGISTERING, calls notifiers

with NETDEV_UNREGISTER, and adds the device to the todo list.

Later on, devices in the todo list are processed by netdev_run_todo().

netdev_run_todo() waits devices' reference count become 1 while

rebdoadcasting NETDEV_UNREGISTER notification.

When cfusbl_device_notify() is called with NETDEV_UNREGISTER multiple

times, the parent device might be freed. This could cause UAF.

Processing NETDEV_UNREGISTER multiple times also causes inbalance of

reference count for the module.

This patch fixes the issue by accepting only first NETDEV_UNREGISTER

notification.