Re: [Qemu-devel] [PATCH] scsi: check current request object before use

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/12/2017 12:21, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> During a dma access, SCSIRequest object 'current_req' could be
> null, leading to a null pointer dereference. Add check to avoid
> it.
> 
> Reported-by: Zhangboxian <zhangboxian@huawei.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>

Sorry, this needs a test case.

Paolo

> ---
>  hw/scsi/esp.c      | 2 +-
>  hw/scsi/scsi-bus.c | 3 +++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index ee586e7d6c..0c6925a708 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -273,7 +273,7 @@ static void esp_do_dma(ESPState *s)
>          s->ti_size += len;
>      else
>          s->ti_size -= len;
> -    if (s->async_len == 0) {
> +    if (s->current_req && s->async_len == 0) {
>          scsi_req_continue(s->current_req);
>          /* If there is still data to be read from the device then
>             complete the DMA operation immediately.  Otherwise defer
> diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
> index 977f7bce1f..ac64a239e9 100644
> --- a/hw/scsi/scsi-bus.c
> +++ b/hw/scsi/scsi-bus.c
> @@ -1338,6 +1338,9 @@ void scsi_req_unref(SCSIRequest *req)
>     will start the next chunk or complete the command.  */
>  void scsi_req_continue(SCSIRequest *req)
>  {
> +    if (!req) {
> +        return;
> +    }
>      if (req->io_canceled) {
>          trace_scsi_req_continue_canceled(req->dev->id, req->lun, req->tag);
>          return;
>