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Re: [PATCH] fdc: check null block pointer before blk_pwrite
From: |
Li Qiang |
Subject: |
Re: [PATCH] fdc: check null block pointer before blk_pwrite |
Date: |
Fri, 18 Sep 2020 18:52:18 +0800 |
P J P <ppandit@redhat.com> 于2020年8月27日周四 下午7:41写道:
>
> 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.
>
> -> 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));
> --
Hello Prasad,
There are several pattern to address this NULL check in fdc.c.
I think it is better to consider this as an error. Just like the check
in 'fdctrl_format_sector':
if (cur_drv->blk == NULL ||
blk_pwrite(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo,
BDRV_SECTOR_SIZE, 0) < 0) {
FLOPPY_DPRINTF("error formatting sector %d\n", fd_sector(cur_drv));
fdctrl_stop_transfer(fdctrl, FD_SR0_ABNTERM | FD_SR0_SEEK, 0x00, 0x00);
} else {
Also there seems exists the same issue in 'fdctrl_read_data'
Thanks,
Li Qiang
> 2.26.2
>
>