Re: [PATCH] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

[Avihai Horon <avihaih@nvidia.com>]

On 03/07/2023 19:56, Philippe Mathieu-Daudé wrote:
> External email: Use caution opening links or attachments
>
>
> On 3/7/23 18:39, Avihai Horon wrote:
>> vfio_realize() has the following flow:
>> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
>> 2. msix_early_setup().
>> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
>>
>> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
>> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
>> allocated.
>>
>> In this case, vfio_bars_finalize() is called as part of the error flow
>> to free the bars' resources. However, vfio_bars_finalize() calls
>> object_unparent() for VFIOBAR->mr unconditionally and thus we get a null
>> pointer dereference.
>>
>> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().
>>
>> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
>> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
>> ---
>>   hw/vfio/pci.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index ab6645ba60..95e077082b 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -1752,7 +1752,7 @@ static void vfio_bars_finalize(VFIOPCIDevice 
>> *vdev)
>>
>>           vfio_bar_quirk_finalize(vdev, i);
>>           vfio_region_finalize(&bar->region);
>> -        if (bar->size) {
>> +        if (bar->size && bar->mr) {
>>               object_unparent(OBJECT(bar->mr));
>>               g_free(bar->mr);
>>           }
>
> What about:
>
>             if (bar->mr) {
>                 assert(bar->size);
>                 object_unparent(OBJECT(bar->mr));
>                 g_free(bar->mr);
>                 bar->mr = NULL;
>             }
>
> ?

Nice touch, it's indeed more accurate.

Will change and post v2.

Thanks!