CVE-2024-36479 — fpga: bridge: add owner module and take its refcount

Affected: Linux

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

fpga: bridge: add owner module and take its refcount

The current implementation of the fpga bridge assumes that the low-level module registers a driver for the parent device and uses its owner pointer to take the module's refcount. This approach is problematic since it can lead to a null pointer dereference while attempting to get the bridge if the parent device does not have a driver.

To address this problem, add a module owner pointer to the fpga_bridge struct and use it to take the module's refcount. Modify the function for registering a bridge to take an additional owner module parameter and rename it to avoid conflicts. Use the old function name for a helper macro that automatically sets the module that registers the bridge as the owner. This ensures compatibility with existing low-level control modules and reduces the chances of registering a bridge without setting the owner.

Also, update the documentation to keep it consistent with the new interface for registering an fpga bridge.

Other changes: opportunistically move put_device() from __fpga_bridge_get() to fpga_bridge_get() and of_fpga_bridge_get() to improve code clarity since the bridge device is taken in these functions.

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CVE-2024-36479 — fpga: bridge: add owner module and take its refcount