Describe CVE-2021-47424.
What is CVE-2021-47424?
In the Linux kernel, the following vulnerability has been resolved:

i40e: Fix freeing of uninitialized misc IRQ vector

When VSI set up failed in i40e_probe() as part of PF switch set up
driver was trying to free misc IRQ vectors in
i40e_clear_interrupt_scheme and produced a kernel Oops:

   Trying to free already-free IRQ 266
   WARNING: CPU: 0 PID: 5 at kernel/irq/manage.c:1731 __free_irq+0x9a/0x300
   Workqueue: events work_for_cpu_fn
   RIP: 0010:__free_irq+0x9a/0x300
   Call Trace:
   ? synchronize_irq+0x3a/0xa0
   free_irq+0x2e/0x60
   i40e_clear_interrupt_scheme+0x53/0x190 [i40e]
   i40e_probe.part.108+0x134b/0x1a40 [i40e]
   ? kmem_cache_alloc+0x158/0x1c0
   ? acpi_ut_update_ref_count.part.1+0x8e/0x345
   ? acpi_ut_update_object_reference+0x15e/0x1e2
   ? strstr+0x21/0x70
   ? irq_get_irq_data+0xa/0x20
   ? mp_check_pin_attr+0x13/0xc0
   ? irq_get_irq_data+0xa/0x20
   ? mp_map_pin_to_irq+0xd3/0x2f0
   ? acpi_register_gsi_ioapic+0x93/0x170
   ? pci_conf1_read+0xa4/0x100
   ? pci_bus_read_config_word+0x49/0x70
   ? do_pci_enable_device+0xcc/0x100
   local_pci_probe+0x41/0x90
   work_for_cpu_fn+0x16/0x20
   process_one_work+0x1a7/0x360
   worker_thread+0x1cf/0x390
   ? create_worker+0x1a0/0x1a0
   kthread+0x112/0x130
   ? kthread_flush_work_fn+0x10/0x10
   ret_from_fork+0x1f/0x40

The problem is that at that point misc IRQ vectors
were not allocated yet and we get a call trace
that driver is trying to free already free IRQ vectors.

Add a check in i40e_clear_interrupt_scheme for __I40E_MISC_IRQ_REQUESTED
PF state before calling i40e_free_misc_vector. This state is set only if
misc IRQ vectors were properly initialized..