CVE-2022-50339

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

Bluetooth: avoid hci_dev_test_and_set_flag() in mgmt_init_hdev()

syzbot is again reporting attempt to cancel uninitialized work at mgmt_index_removed() [1], for setting of HCI_MGMT flag from mgmt_init_hdev() from hci_mgmt_cmd() from hci_sock_sendmsg() can race with testing of HCI_MGMT flag from mgmt_index_removed() from hci_sock_bind() due to lack of serialization via hci_dev_lock().

Since mgmt_init_hdev() is called with mgmt_chan_list_lock held, we can safely split hci_dev_test_and_set_flag() into hci_dev_test_flag() and hci_dev_set_flag(). Thus, in order to close this race, set HCI_MGMT flag after INIT_DELAYED_WORK() completed.

This is a local fix based on mgmt_chan_list_lock. Lack of serialization via hci_dev_lock() might be causing different race conditions somewhere else. But a global fix based on hci_dev_lock() should deserve a future patch.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/e53c6180db8dd09de94e0a3bdf4fef6f5f9dd6e6
• https://git.kernel.org/stable/c/f74ca25d6d6629ffd4fd80a1a73037253b57d06b