CVE-2025-38584

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

padata: Fix pd UAF once and for all

There is a race condition/UAF in padata_reorder that goes back

to the initial commit. A reference count is taken at the start

of the process in padata_do_parallel, and released at the end in

padata_serial_worker.

This reference count is (and only is) required for padata_replace

to function correctly. If padata_replace is never called then

there is no issue.

In the function padata_reorder which serves as the core of padata,

as soon as padata is added to queue->serial.list, and the associated

spin lock released, that padata may be processed and the reference

count on pd would go away.

Fix this by getting the next padata before the squeue->serial lock

is released.

In order to make this possible, simplify padata_reorder by only

calling it once the next padata arrives.