CVE-2025-40308: 
Linux Kernel vulnerability analysis and mitigation

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

Bluetooth: bcsp: receive data only if registered

Currently, bcsp_recv() can be called even when the BCSP protocol has not been registered. This leads to a NULL pointer dereference, as shown in the following stack trace:

KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f]
RIP: 0010:bcsp_recv+0x13d/0x1740 drivers/bluetooth/hci_bcsp.c:590
Call Trace:
 <TASK>
 hci_uart_tty_receive+0x194/0x220 drivers/bluetooth/hci_ldisc.c:627
 tiocsti+0x23c/0x2c0 drivers/tty/tty_io.c:2290
 tty_ioctl+0x626/0xde0 drivers/tty/tty_io.c:2706
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

To prevent this, ensure that the HCI_UART_REGISTERED flag is set before processing received data. If the protocol is not registered, return -EUNATCH.