Re: [PATCH] pci: check bus pointer before dereference

[Li Qiang]

P J P <ppandit@redhat.com> 于2020年8月27日周四 下午7:52写道：
>
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While mapping IRQ level in pci_change_irq_level() routine,
> it does not check if pci_get_bus() returned a valid pointer.
> It may lead to a NULL pointer dereference issue. Add check to
> avoid it.
>
>  -> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Flsi_nullptr1
>     ==1183858==Hint: address points to the zero page.
>     #0 pci_change_irq_level hw/pci/pci.c:259
>     #1 pci_irq_handler hw/pci/pci.c:1445
>     #2 pci_set_irq hw/pci/pci.c:1463
>     #3 lsi_set_irq hw/scsi/lsi53c895a.c:488
>     #4 lsi_update_irq hw/scsi/lsi53c895a.c:523
>     #5 lsi_script_scsi_interrupt hw/scsi/lsi53c895a.c:554
>     #6 lsi_execute_script hw/scsi/lsi53c895a.c:1149
>     #7 lsi_reg_writeb hw/scsi/lsi53c895a.c:1984
>     #8 lsi_io_write hw/scsi/lsi53c895a.c:2146
>     ...
>
> Reported-by: Ruhr-University <bugs-syssec@rub.de>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/pci/pci.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index de0fae10ab..df5a2c3294 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -253,6 +253,9 @@ static void pci_change_irq_level(PCIDevice *pci_dev, int 
> irq_num, int change)
>      PCIBus *bus;
>      for (;;) {
>          bus = pci_get_bus(pci_dev);
> +        if (!bus) {

Hi Prasad,

I think in normal this 'bus' will be not NULL.
I have look at the link in the commit msg.
I find it is another DMA to MMIO issue which we have discussed a lot
but didn't come up with an
satisfying solution.

Maybe we can try to the DMA to MMIO issue direction.
CC: Peter, Jason and Alex

Thanks,
Li Qiang


> +            return;
> +        }
>          irq_num = bus->map_irq(pci_dev, irq_num);
>          if (bus->set_irq)
>              break;
> --
> 2.26.2
>
>