Executive Summary

This vulnerability exists in the Linux kernel's Bluetooth subsystem, specifically in the hci_ldisc component. When the function hci_register_dev() fails during the process of registering a device in hci_uart_register_dev(), a flag called HCI_UART_PROTO_INIT is not cleared before the protocol's close function is called and the device pointer is set to NULL.

Because the flag is not cleared, incoming UART data can still reach the protocol-specific receive handler (hci_uart_tty_receive()) after the associated resources have been freed. This can lead to unsafe behavior such as accessing invalid memory.

The fix involves clearing the HCI_UART_PROTO_INIT flag with a write lock before calling the protocol's close function and setting the device pointer to NULL. This write lock ensures that all active readers have finished and no new readers can enter the receive path before resources are freed, preventing potential null pointer dereferences.

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Impact Analysis

This vulnerability can lead to unsafe memory access in the Bluetooth subsystem of the Linux kernel. Specifically, it may cause null pointer dereferences or other memory corruption issues when incoming UART data is processed after the related resources have been freed.

Such issues can result in system instability, crashes, or potentially allow an attacker to execute arbitrary code or cause denial of service by exploiting the improper handling of Bluetooth UART data.

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Mitigation Strategies

The vulnerability is resolved by clearing the HCI_UART_PROTO_INIT flag with a write lock before calling the protocol close function and setting the device pointer to NULL. To mitigate this vulnerability, you should update your Linux kernel to a version that includes this fix.

This update ensures that incoming UART data does not reach protocol-specific receive handlers after resources are freed, preventing potential null pointer dereferences.

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