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

HID: logitech-hidpp: Fix kernel crash on receiver USB disconnect

hidpp_connect_event() has four time-of-check vs time-of-use (TOCTOU)
races when it races with itself.

hidpp_connect_event() primarily runs from a workqueue but it also runs
on probe() and if a “device-connected” packet is received by the hw
when the thread running hidpp_connect_event() from probe() is waiting on
the hw, then a second thread running hidpp_connect_event() will be
started from the workqueue.

This opens the following races (note the below code is simplified):

1. Retrieving + printing the protocol (harmless race):

   if (!hidpp->protocol_major) {

   hidpp_root_get_protocol_version()
   hidpp->protocol_major = response.rap.params[0];
   

   }

We can actually see this race hit in the dmesg in the abrt output
attached to rhbz#2227968:

[ 3064.624215] logitech-hidpp-device 0003:046D:4071.0049: HID++ 4.5 device connected.
[ 3064.658184] logitech-hidpp-device 0003:046D:4071.0049: HID++ 4.5 device connected.

Testing with extra logging added has shown that after this the 2 threads
take turn grabbing the hw access mutex (send_mutex) so they ping-pong
through all the other TOCTOU cases managing to hit all of them:

1. Updating the name to the HIDPP name (harmless race):

   if (hidpp->name == hdev->name) {

   ...
   hidpp->name = new_name;
   

   }

2. Initializing the power_supply class for the battery (problematic!):

hidpp_initialize_battery()
{

    if (hidpp->battery.ps)
            return 0;

probe_battery(); /* Blocks, threads take turns executing this */

hidpp->battery.desc.properties =
	devm_kmemdup(dev, hidpp_battery_props, cnt, GFP_KERNEL);

hidpp->battery.ps =
	devm_power_supply_register(&hidpp->hid_dev->dev,
				   &hidpp->battery.desc, cfg);

}

1. Creating delayed input_device (potentially problematic):

   if (hidpp->delayed_input)

   return;
   

   hidpp->delayed_input = hidpp_allocate_input(hdev);

The really big problem here is 3. Hitting the race leads to the following
sequence:

hidpp->battery.desc.properties =
	devm_kmemdup(dev, hidpp_battery_props, cnt, GFP_KERNEL);

hidpp->battery.ps =
	devm_power_supply_register(&hidpp->hid_dev->dev,
				   &hidpp->battery.desc, cfg);

...

hidpp->battery.desc.properties =
	devm_kmemdup(dev, hidpp_battery_props, cnt, GFP_KERNEL);

hidpp->battery.ps =
	devm_power_supply_register(&hidpp->hid_dev->dev,
				   &hidpp->battery.desc, cfg);

So now we have registered 2 power supplies for the same battery,
which looks a bit weird from userspace’s pov but this is not even
the really big problem.

Notice how:

1. This is all devm-maganaged
   
2. The hidpp->battery.desc struct is shared between the 2 power supplies
   
3. hidpp->battery.desc.properties points to the result from the second
   devm_kmemdup()
   

This causes a use after free scenario on USB disconnect of the receiver:

1. The last registered power supply class device gets unregistered
   
2. The memory from the last devm_kmemdup() call gets freed,
   hidpp->battery.desc.properties now points to freed memory
   
3. The first registered power supply class device gets unregistered,
   this involves sending a remove uevent to userspace which invokes
   power_supply_uevent() to fill the uevent data
   
4. power_supply_uevent() uses hidpp->battery.desc.properties which
   now points to freed memory leading to backtraces like this one:
   

Sep 22 20:01:35 eric kernel: BUG: unable to handle page fault for address: ffffb2140e017f08
…
Sep 22 20:01:35 eric kernel: Workqueue: usb_hub_wq hub_event
Sep 22 20:01:35 eric kernel: RIP: 0010:power_supply_uevent+0xee/0x1d0
…
Sep 22 20:01:35 eric kernel: ? asm_exc_page_fault+0x26/0x30
Sep 22 20:01:35 eric kernel: ? power_supply_uevent+0xee/0x1d0
Sep 22 20:01:35 eric kernel: ? power_supply_uevent+0x10d/0x1d0
Sep 22 20:01:35 eric kernel: dev_uevent+0x10f/0x2d0
Sep 22 20:01:35 eric kernel: kobject_uevent_env+0x291/0x680
Sep 22 20:01:35 eric kernel:
—-truncated—-