Subject: Re: [PATCH v7 net-next 2/8] dpll: allow registering FW-identified pin with a different DPLL

From: Jakub Kicinski <[email-masked]>
Date: Sat, 2 May 2026 10:27:15 -0700

On Thu, 30 Apr 2026 11:42:32 +0200 Grzegorz Nitka wrote:
> Relax the (module, clock_id) equality requirement when registering a
> pin identified by firmware (pin->fwnode). Some platforms associate a
> FW-described pin with a DPLL instance that differs from the pin's
> (module, clock_id) tuple. For such pins, permit registration without
> requiring the strict match. Non-FW pins still require equality.

AI asks what prevents the modules from disappearing:

Does this relaxed check expose pin->module to a use-after-free during
netlink queries?
If module A registers a firmware-described pin allocated by module B,
they will have different module pointers. 
Because fwnode_dpll_pin_find() increases the pin's refcount but does
not take a reference to module B via try_module_get(), it appears module B
could be unloaded while module A still holds an active reference to the pin.
When module B unloads, its struct module memory is freed, leaving
pin->module as a dangling pointer.
A subsequent user-space Netlink query using DPLL_CMD_PIN_GET iterates over
the registered pins and calls nla_put_string() with module_name(pin->module),
which would dereference the freed module memory.