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

[Kevin Wolf <kwolf@redhat.com>]

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