padata: avoid UAF for reorder_work

JIRA: https://issues.redhat.com/browse/RHEL-81531
CVE: CVE-2025-21726

commit dd7d37c
Author: Chen Ridong <chenridong@huawei.com>
Date:   Fri, 10 Jan 2025 06:16:39 +0000

    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.

    Fixes: bbefa1d ("crypto: pcrypt - Avoid deadlock by using per-instance padata queues")
    Signed-off-by: Chen Ridong <chenridong@huawei.com>
    Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

kernel/padata.c

@@ -352,8 +352,14 @@ static void padata_reorder(struct parallel_data *pd)
 	smp_mb();
 
 	reorder = per_cpu_ptr(pd->reorder_list, pd->cpu);
-	if (!list_empty(&reorder->list) && padata_find_next(pd, false))
+	if (!list_empty(&reorder->list) && padata_find_next(pd, false)) {
+		/*
+		 * Other context(eg. the padata_serial_worker) can finish the request.
+		 * To avoid UAF issue, add pd ref here, and put pd ref after reorder_work finish.
+		 */
+		padata_get_pd(pd);
 		queue_work(pinst->serial_wq, &pd->reorder_work);
+	}
 }
 
 static void invoke_padata_reorder(struct work_struct *work)
@@ -364,6 +370,8 @@ static void invoke_padata_reorder(struct work_struct *work)
 	pd = container_of(work, struct parallel_data, reorder_work);
 	padata_reorder(pd);
 	local_bh_enable();
+	/* Pairs with putting the reorder_work in the serial_wq */
+	padata_put_pd(pd);
 }
 
 static void padata_serial_worker(struct work_struct *serial_work)