CVE-2024-26806: Improper Locking

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

spi: cadence-qspi: remove system-wide suspend helper calls from runtime PM hooks

The ->runtime_suspend() and ->runtime_resume() callbacks are not expected to call spi_controller_suspend() and spi_controller_resume(). Remove calls to those in the cadence-qspi driver.

Those helpers have two roles currently: - They stop/start the queue, including dealing with the kworker. - They toggle the SPI controller SPI_CONTROLLER_SUSPENDED flag. It requires acquiring ctlr->bus_lock_mutex.

Step one is irrelevant because cadence-qspi is not queued. Step two however has two implications: - A deadlock occurs, because ->runtime_resume() is called in a context where the lock is already taken (in the ->exec_op() callback, where the usage count is incremented). - It would disallow all operations once the device is auto-suspended.

Here is a brief call tree highlighting the mutex deadlock:

spi_mem_exec_op() ... spi_mem_access_start() mutex_lock(&ctlr->bus_lock_mutex)

cqspi_exec_mem_op() pm_runtime_resume_and_get() cqspi_resume() spi_controller_resume() mutex_lock(&ctlr->bus_lock_mutex) ...

spi_mem_access_end() mutex_unlock(&ctlr->bus_lock_mutex) ...