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: __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

When unregistering a net device, unregister_netdevice_many_notify() sets the devices 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.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/1793da97a23e31c5bf06631f3f3e5a25f368fd64
• https://git.kernel.org/stable/c/287027d8a567168a5d8ce5cb0cba16a34791a48c
• https://git.kernel.org/stable/c/3f14457e1584224f4296af613bbd99deb60b5d91
• https://git.kernel.org/stable/c/68a45c3cf0e2242a533657f4f535d9b6a7447a79
• https://git.kernel.org/stable/c/9781e98a97110f5e76999058368b4be76a788484
• https://git.kernel.org/stable/c/9dc16be373b382ddd4c274052a6e870a95e76c01
• https://git.kernel.org/stable/c/c3aaec463a632cf4187dc017e421bfa69d7834a9
• https://git.kernel.org/stable/c/d1a11bbdbb5ea9f172019c5a4a3e9d8eabd72179