CVE-2025-21726

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

padata: avoid UAF for reorder_work

Although the previous patch can avoid ps and ps UAF for _do_serial, it
can not avoid potential UAF issue for reorder_work. This issue can
happen just as below:

crypto_request crypto_request crypto_del_alg
padata_do_serial
...
padata_reorder
// processes all remaining
// requests then breaks
while (1) {
if (!padata)
break;
...
}

padata_do_serial
// new request added
list_add
// sees the new request
queue_work(reorder_work)
padata_reorder
queue_work_on(squeue->work)
...

<kworker context>
padata_serial_worker
// completes new request,
// no more outstanding
// requests

crypto_del_alg
// free pd

<kworker context>
invoke_padata_reorder
// UAF of pd

To avoid UAF for 'reorder_work', get 'pd' ref before put 'reorder_work'
into the 'serial_wq' and put 'pd' ref until the 'serial_wq' finish.