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

[John Snow]

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!