net: enetc: fix init and teardown order to prevent use of unsafe resources

Sashiko reported a potential issue in enetc_msg_psi_init() where the IRQ
handler is registered before DMA resources are fully initialized [1].

The current initialization sequence is:

  1. request_irq(enetc_msg_psi_msix)    <- IRQ handler registered
  2. INIT_WORK(&pf->msg_task, ...)      <- work_struct initialized
  3. enetc_msg_alloc_mbx()              <- mailbox DMA allocated

This ordering is unsafe because if a spurious interrupt or pending
interrupt from a previous device state fires immediately after
request_irq() returns, the registered ISR enetc_msg_psi_msix() will
execute and unconditionally call:

  schedule_work(&pf->msg_task)

At this point, pf->msg_task has not been initialized by INIT_WORK(), so
the work_struct contains garbage values in its internal linked list
pointers (work_struct->entry). Passing an uninitialized work_struct to
schedule_work() could corrupt the kernel's workqueue linked lists,
potentially leading to:

  - Kernel panic in __queue_work()
  - Memory corruption in workqueue data structures
  - System deadlock or undefined behavior

Additionally, even if the work_struct was initialized, the mailbox DMA
buffers (pf->rxmsg[]) may not yet be allocated when the work handler
enetc_msg_task() runs, resulting in NULL pointer dereference.

Fix by reordering the initialization sequence to ensure all resources are
properly initialized before the interrupt handler can execute:

  1. enetc_msg_alloc_mbx()              <- Allocate all mailboxes
  2. INIT_WORK(&pf->msg_task, ...)      <- Initialize work first
  3. request_irq(enetc_msg_psi_msix)    <- Register IRQ last
  4. Configure hardware & enable MR interrupts

This guarantees that when enetc_msg_psi_msix() runs:
  - pf->msg_task is properly initialized (safe for schedule_work)
  - pf->rxmsg[] buffers are allocated (safe for work handler access)
  - Hardware is configured appropriately

As the inverse of enetc_msg_psi_init(), enetc_msg_psi_free() also has
similar problems. For example, if a pending interrupt fires between
enetc_msg_free_mbx() and free_irq(), the ISR enetc_msg_psi_msix() may
schedule the work handler again via schedule_work(), which could then
access already-freed DMA buffers (pf->rxmsg[]), leading to use-after-free
and potential memory corruption.

Therefore, the order of enetc_msg_psi_free() is adjusted:
  1. enetc_msg_disable_mr_int()       <- Stop new interrupts first
  2. free_irq()                       <- Ensure no IRQ handler can run
  3. cancel_work_sync()               <- Wait for any pending work
  4. enetc_msg_disable_mr_int()       <- Re-disable in case work
					 re-enabled it
  5. enetc_msg_free_mbx()             <- Safe to free DMA buffers now

Link: https://sashiko.dev/#/patchset/20260511080805.2052495-1-wei.fang%40nxp.com #1
Fixes: beb74ac ("enetc: Add vf to pf messaging support")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Link: https://patch.msgid.link/20260520064421.91569-9-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: WeiFang-NXP

drivers/net/ethernet/freescale/enetc/enetc_msg.c

@@ -118,6 +118,15 @@ int enetc_msg_psi_init(struct enetc_pf *pf)
 	struct enetc_si *si = pf->si;
 	int vector, i, err;
 
+	for (i = 0; i < pf->num_vfs; i++) {
+		err = enetc_msg_alloc_mbx(si, i);
+		if (err)
+			goto free_mbx;
+	}
+
+	/* initialize PSI mailbox */
+	INIT_WORK(&pf->msg_task, enetc_msg_task);
+
 	/* register message passing interrupt handler */
 	snprintf(pf->msg_int_name, sizeof(pf->msg_int_name), "%s-vfmsg",
 		 si->ndev->name);
@@ -126,32 +135,21 @@ int enetc_msg_psi_init(struct enetc_pf *pf)
 	if (err) {
 		dev_err(&si->pdev->dev,
 			"PSI messaging: request_irq() failed!\n");
-		return err;
+		goto free_mbx;
 	}
 
 	/* set one IRQ entry for PSI message receive notification (SI int) */
 	enetc_wr(&si->hw, ENETC_SIMSIVR, ENETC_SI_INT_IDX);
 
-	/* initialize PSI mailbox */
-	INIT_WORK(&pf->msg_task, enetc_msg_task);
-
-	for (i = 0; i < pf->num_vfs; i++) {
-		err = enetc_msg_alloc_mbx(si, i);
-		if (err)
-			goto err_init_mbx;
-	}
-
 	/* enable MR interrupts */
 	enetc_msg_enable_mr_int(pf);
 
 	return 0;
 
-err_init_mbx:
+free_mbx:
 	for (i--; i >= 0; i--)
 		enetc_msg_free_mbx(si, i);
 
-	free_irq(vector, si);
-
 	return err;
 }
 
@@ -160,14 +158,17 @@ void enetc_msg_psi_free(struct enetc_pf *pf)
 	struct enetc_si *si = pf->si;
 	int i;
 
+	/* disable MR interrupts */
+	enetc_msg_disable_mr_int(pf);
+
+	/* de-register message passing interrupt handler */
+	free_irq(pci_irq_vector(si->pdev, ENETC_SI_INT_IDX), si);
+
 	cancel_work_sync(&pf->msg_task);
 
-	/* disable MR interrupts */
+	/* MR interrupts may be re-enabled by workqueue */
 	enetc_msg_disable_mr_int(pf);
 
 	for (i = 0; i < pf->num_vfs; i++)
 		enetc_msg_free_mbx(si, i);
-
-	/* de-register message passing interrupt handler */
-	free_irq(pci_irq_vector(si->pdev, ENETC_SI_INT_IDX), si);
 }