CVE-2023-52478: 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:  2. Updating the name to the HIDPP name (harmless race):   if (hidpp->name == hdev->name) {   ...   hidpp->name = new_name;  }  3. 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); }  4. 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---