Medium [CVE-2026-80678] Fix slave registration race and error handling

In the Linux kernel, the following vulnerability has been resolved: i2c: imx: Fix slave registration race and error handling In i2c_imx_reg_slave(), the slave pointer was assigned before pm_runtime_resume_and_get().

If pm_runtime_resume_and_get() failed, the error path returned without clearing i2c_imx->slave, leaving it non-NULL and causing all subsequent registration attempts to fail with -EBUSY. Additionally, because this driver uses a shared IRQ, the interrupt handler i2c_imx_isr() can execute concurrently and, after acquiring slave_lock, dereference i2c_imx->slave.

The previous fix attempt added a lockless i2c_imx->slave = NULL on the error path, but that could race with the ISR under the lock and still cause a NULL pointer dereference.

Fix both issues by deferring the assignment of i2c_imx->slave and i2c_imx->last_slave_event to after a successful resume, and by performing the assignment inside the slave_lock critical section. This guarantees that the slave pointer is never left stale on the error path and is always valid when observed by the interrupt handler.

This occurs when the i2c_imx->slave pointer is not properly cleared or assigned, especially if power management operations fail or if the interrupt handler executes concurrently. A local attacker could potentially exploit this to cause a system crash, resulting in a Denial of Service (DoS).