Re: [PATCH v2] fdc: check null block pointer before r/w data transfer

[Li Qiang]

P J P <ppandit@redhat.com> 于2020年9月22日周二 下午5:29写道：
>
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While transferring data via fdctrl_read/write_data() routines,
> check that current drive does not have a null block pointer.
> Avoid null pointer dereference.
>
>  -> 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>

Reviewed-by: Li Qiang <liq3ea@gmail.com>

> ---
>  hw/block/fdc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> Update v2: treat NULL blk pointer as an error
>   -> https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg06642.html
>
> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
> index 224bac504f..bf968dc66f 100644
> --- a/hw/block/fdc.c
> +++ b/hw/block/fdc.c
> @@ -1923,7 +1923,8 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl)
>                                     fd_sector(cur_drv));
>                      return 0;
>                  }
> -            if (blk_pread(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo,
> +            if (!cur_drv->blk
> +                || blk_pread(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo,
>                            BDRV_SECTOR_SIZE)
>                  < 0) {
>                  FLOPPY_DPRINTF("error getting sector %d\n",
> @@ -2427,7 +2428,8 @@ 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));
> --
> 2.26.2
>