Re: [PATCH] fdc: check null block pointer before blk_pwrite

[John Snow]

On 8/27/20 7:38 AM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While transferring data via fdctrl_write_data(), check that
> current drive does not have a null block pointer. Avoid
> null pointer dereference.

Hi PJP. I assume this patch actually covers the exact same thing that 
the other if cur_drv->blk patch we have been discussing recently does.

You may want to combine the Reported-By lines for both.

I am dropping this patch from my queue in favor of pursuing our other, 
more recent and active thread, which I am also now tracking via this 
gitlab issue:

https://gitlab.com/qemu-project/qemu/-/issues/338

>   -> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Ffdc_nullptr1
>      ==1658854==Hint: address points to the zero page.
>      #0 blk_inc_in_flight block/block-backend.c:1327
>      #1 blk_prw block/block-backend.c:1299
>      #2 blk_pwrite block/block-backend.c:1464
>      #3 fdctrl_write_data hw/block/fdc.c:2418
>      #4 fdctrl_write hw/block/fdc.c:962
>      #5 portio_write ioport.c:205
>      #6 memory_region_write_accessor memory.c:483
>      #7 access_with_adjusted_size memory.c:544
>      #8 memory_region_dispatch_write memory.c:1476
>
> Reported-by: Ruhr-University <bugs-syssec@rub.de>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>   hw/block/fdc.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
> index e9ed3eef45..dedadac68a 100644
> --- a/hw/block/fdc.c
> +++ b/hw/block/fdc.c
> @@ -2419,7 +2419,8 @@ static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t 
> value)
>           if (pos == FD_SECTOR_LEN - 1 ||
>               fdctrl->data_pos == fdctrl->data_len) {
>               cur_drv = get_cur_drv(fdctrl);
> -            if (blk_pwrite(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo,
> +            if (cur_drv->blk
> +                && blk_pwrite(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo,
>                              BDRV_SECTOR_SIZE, 0) < 0) {
>                   FLOPPY_DPRINTF("error writing sector %d\n",
>                                  fd_sector(cur_drv));