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

[John Snow <jsnow@redhat.com>]

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?

--js