CVE-2026-99015: Bluetooth: hci_sock: Serialize dead-device detachment

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

Bluetooth: hcisock: Serialize dead-device detachment

Rebinding an HCI socket after its controller is unregistered can race monitor control replay and crash the kernel. hcisockbind() clears hcipi(sk)->hdev and drops the device reference under only the socket lock, whereas sendmonitorcontrolreplay() holds hcisklist.lock for reading.

Replay can observe a non-NULL hdev, then bind can clear it and drop the last reference before createmonitorctrlopen() reads hdev->id. This can cause a NULL pointer dereference if the pointer is reloaded, or a use-after-free if the old pointer is retained.

The kernel reported:

KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] RIP: 0010:createmonitorctrlopen+0x579/0x800 Call Trace: hcisockbind+0xd96/0x1190 sysbind+0x166/0x200 x64sysbind+0x6d/0xb0 dosyscall64+0xdd/0x4a0 entrySYSCALL64afterhwframe+0x77/0x7f

The same missing serialization lets hcisendtosock() select a socket for the old device and queue its frame after bind has detached the socket or installed a new binding.

Take hcisklist.lock for writing when clearing the device pointer and resetting the socket state. This waits for existing replay and delivery readers to finish before detachment and prevents later readers from using the old binding. Keep hcidevput() outside the critical section because the final device release can sleep.