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

[Kevin Wolf <kwolf@redhat.com>]

Am 18.11.2018 um 13:32 hat Mark Cave-Ayland geschrieben:
> 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 <martin@duskware.de>
> >>>> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> >>>> ---
> >>>>  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 <jsnow@redhat.com>
> >>>
> >>> ... 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.

Ok, done. Also actually CCed qemu-stable on this mail.

Kevin