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

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
Fixes: beb74ac878c8 ("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>