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

[P J P]

+-- On Thu, 27 Aug 2020, P J P wrote --+
| 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));
| 

Ping...!
--
Prasad J Pandit / Red Hat Product Security Team
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