Re: [Qemu-devel] [PATCH for-3.1] fdc: fix segfault in fdctrl_stop_transfer() when DMA is disabled

[Mark Cave-Ayland]

On 13/11/2018 20:29, John Snow wrote:

> On 11/13/18 8:16 AM, Kevin Wolf wrote:
>> Am 12.11.2018 um 20:58 hat John Snow geschrieben:
>>>
>>>
>>> On 11/11/18 4:40 AM, Mark Cave-Ayland wrote:
>>>> Commit c8a35f1cf0f "fdc: use IsaDma interface instead of global DMA_*
>>>> functions" accidentally introduced a segfault in fdctrl_stop_transfer() for
>>>> non-DMA transfers.
>>>>
>>>> If fdctrl->dma_chann has not been configured then the fdctrl->dma interface
>>>> reference isn't initialised during isabus_fdc_realize(). Unfortunately
>>>> fdctrl_stop_transfer() unconditionally references the DMA interface when
>>>> finishing the transfer causing a NULL pointer dereference.
>>>>
>>>> Fix the issue by adding a check in fdctrl_stop_transfer() so that the DMA
>>>> interface reference and release method is only invoked if fdctrl->dma_chann
>>>> has been set.
>>>>
>>>> (This issue was discovered by Martin testing a recent change in the NetBSD
>>>> installer under qemu-system-sparc)
>>>>
>>>> Reported-by: Martin Husemann <address@hidden>
>>>> Signed-off-by: Mark Cave-Ayland <address@hidden>
>>>> ---
>>>>  hw/block/fdc.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
>>>> index 2e9c1e1e2f..6f19f127a5 100644
>>>> --- a/hw/block/fdc.c
>>>> +++ b/hw/block/fdc.c
>>>> @@ -1617,7 +1617,7 @@ static void fdctrl_stop_transfer(FDCtrl *fdctrl, 
>>>> uint8_t status0,
>>>>      fdctrl->fifo[5] = cur_drv->sect;
>>>>      fdctrl->fifo[6] = FD_SECTOR_SC;
>>>>      fdctrl->data_dir = FD_DIR_READ;
>>>> -    if (!(fdctrl->msr & FD_MSR_NONDMA)) {
>>>> +    if (fdctrl->dma_chann != -1 && !(fdctrl->msr & FD_MSR_NONDMA)) {
>>>>          IsaDmaClass *k = ISADMA_GET_CLASS(fdctrl->dma);
>>>>          k->release_DREQ(fdctrl->dma, fdctrl->dma_chann);
>>>>      }
>>>>
>>>
>>> Thanks.
>>>
>>> Reviewed-by: John Snow <address@hidden>
>>>
>>> ... Kevin, would you mind staging this one-off for the next RC?
>>
>> No problem, I'm applying this to my block branch. However, my pull
>> request for -rc1 is already merged, so this will have to wait until next
>> week and -rc2.
>>
>> Kevin
>>
> 
> I think that should be fine. Thank you!

Thanks everyone! Kevin, any chance you could also add a CC: qemu-stable@ tag 
when you
apply this to your branch? This will help ensure that when the next NetBSD 
release
appears the fix should already be available for most people.


ATB,

Mark.