[PATCH net v3 2/2] pds_core: fix use-after-free on workqueue during remove

["Nikhil P. Rao" <nikhil.rao@amd.com>]

In pdsc_remove(), the workqueue is destroyed before pdsc_teardown()
is called. This ordering allows two paths to queue work on the
destroyed workqueue:

1. If pdsc_teardown() -> pdsc_devcmd_reset() times out, the error
   path in pdsc_devcmd_locked() queues health_work.

2. A NotifyQ event can trigger the ISR and queue work before free_irq()
   is called in pdsc_teardown().

Fix by moving destroy_workqueue() after pdsc_teardown() so the
workqueue outlives every queuer; destroy_workqueue() then flushes any
work still pending.

Draining the queued work also requires ordering the teardown so the
resources that work touches are freed last:

  - In pdsc_qcq_free(), after freeing the interrupt, cancel_work_sync()
    the queue's work and only then clear qcq->intx, so
    pdsc_process_adminq()'s read of qcq->intx for interrupt-credit
    return cannot race with the clear.

  - Free adminqcq before notifyqcq: the shared adminq ISR is released
    when adminqcq is freed, and the adminq work accesses notifyqcq, so
    both must be stopped before notifyqcq is freed.

Fixes: 01ba61b55b20 ("pds_core: Add adminq processing and commands")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://patchwork.kernel.org/comment/27002369/
Signed-off-by: Nikhil P. Rao <nikhil.rao@amd.com>
---
 drivers/net/ethernet/amd/pds_core/core.c | 14 ++++++++++----
 drivers/net/ethernet/amd/pds_core/main.c |  5 +++--
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/amd/pds_core/core.c b/drivers/net/ethernet/amd/pds_core/core.c
index 1074a022a52f..e39b2c9beb20 100644
--- a/drivers/net/ethernet/amd/pds_core/core.c
+++ b/drivers/net/ethernet/amd/pds_core/core.c
@@ -110,7 +110,6 @@ static void pdsc_qcq_intr_free(struct pdsc *pdsc, struct pdsc_qcq *qcq)
 		return;
 
 	pdsc_intr_free(pdsc, qcq->intx);
-	qcq->intx = PDS_CORE_INTR_INDEX_NOT_ASSIGNED;
 }
 
 static int pdsc_qcq_intr_alloc(struct pdsc *pdsc, struct pdsc_qcq *qcq)
@@ -145,6 +144,12 @@ void pdsc_qcq_free(struct pdsc *pdsc, struct pdsc_qcq *qcq)
 
 	pdsc_qcq_intr_free(pdsc, qcq);
 
+	/* Drain any work queued by ISR before it was freed above */
+	if (qcq->work.func)
+		cancel_work_sync(&qcq->work);
+
+	qcq->intx = PDS_CORE_INTR_INDEX_NOT_ASSIGNED;
+
 	if (qcq->q_base)
 		dma_free_coherent(dev, qcq->q_size,
 				  qcq->q_base, qcq->q_base_pa);
@@ -304,8 +309,11 @@ int pdsc_qcq_alloc(struct pdsc *pdsc, unsigned int type, unsigned int index,
 
 static void pdsc_core_uninit(struct pdsc *pdsc)
 {
-	pdsc_qcq_free(pdsc, &pdsc->notifyqcq);
+	/* Free adminqcq first: its work accesses notifyqcq, so we must
+	 * disable its IRQ and drain its work before freeing notifyqcq.
+	 */
 	pdsc_qcq_free(pdsc, &pdsc->adminqcq);
+	pdsc_qcq_free(pdsc, &pdsc->notifyqcq);
 
 	if (pdsc->kern_dbpage) {
 		iounmap(pdsc->kern_dbpage);
@@ -479,8 +487,6 @@ void pdsc_teardown(struct pdsc *pdsc, bool removing)
 {
 	if (!pdsc->pdev->is_virtfn)
 		pdsc_devcmd_reset(pdsc);
-	if (pdsc->adminqcq.work.func)
-		cancel_work_sync(&pdsc->adminqcq.work);
 
 	pci_clear_master(pdsc->pdev);
 
diff --git a/drivers/net/ethernet/amd/pds_core/main.c b/drivers/net/ethernet/amd/pds_core/main.c
index 22db78343eb0..638b9c7a509d 100644
--- a/drivers/net/ethernet/amd/pds_core/main.c
+++ b/drivers/net/ethernet/amd/pds_core/main.c
@@ -435,8 +435,6 @@ static void pdsc_remove(struct pci_dev *pdev)
 		pdsc_auxbus_dev_del(pdsc, pdsc, &pdsc->padev);
 
 		timer_shutdown_sync(&pdsc->wdtimer);
-		if (pdsc->wq)
-			destroy_workqueue(pdsc->wq);
 
 		mutex_lock(&pdsc->config_lock);
 		set_bit(PDSC_S_STOPPING_DRIVER, &pdsc->state);
@@ -444,6 +442,9 @@ static void pdsc_remove(struct pci_dev *pdev)
 		pdsc_stop(pdsc);
 		pdsc_teardown(pdsc, PDSC_TEARDOWN_REMOVING);
 		mutex_unlock(&pdsc->config_lock);
+
+		if (pdsc->wq)
+			destroy_workqueue(pdsc->wq);
 		mutex_destroy(&pdsc->config_lock);
 		mutex_destroy(&pdsc->devcmd_lock);
 
-- 
2.43.0