When about to execute a SCSI command, ensure that cmdfifo is not empty and
current_dev is non-NULL. This can happen if the guest tries to execute a TI
(Transfer Information) command without issuing one of the select commands
first.

Buglink: https://bugs.launchpad.net/qemu/+bug/1910723
Buglink: https://bugs.launchpad.net/qemu/+bug/1909247
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
 hw/scsi/esp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
index bbcbfa4a91..ae362c9dfb 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -286,6 +286,9 @@ static void do_busid_cmd(ESPState *s, uint8_t busid)
     trace_esp_do_busid_cmd(busid);
     lun = busid & 7;
     cmdlen = fifo8_num_used(&s->cmdfifo);
+    if (!cmdlen || !s->current_dev) {
+        return;
+    }
     buf = (uint8_t *)fifo8_pop_buf(&s->cmdfifo, cmdlen, &n);
 
     current_lun = scsi_device_find(&s->bus, 0, s->current_dev->id, lun);
-- 
2.20.1

On 210317 2302, Mark Cave-Ayland wrote:
> When about to execute a SCSI command, ensure that cmdfifo is not empty and
> current_dev is non-NULL. This can happen if the guest tries to execute a TI
> (Transfer Information) command without issuing one of the select commands
> first.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1910723
> Buglink: https://bugs.launchpad.net/qemu/+bug/1909247
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>  hw/scsi/esp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 

Tested-by: Alexander Bulekov <alxndr@bu.edu>

> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index bbcbfa4a91..ae362c9dfb 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -286,6 +286,9 @@ static void do_busid_cmd(ESPState *s, uint8_t busid)
>      trace_esp_do_busid_cmd(busid);
>      lun = busid & 7;
>      cmdlen = fifo8_num_used(&s->cmdfifo);
> +    if (!cmdlen || !s->current_dev) {
> +        return;
> +    }
>      buf = (uint8_t *)fifo8_pop_buf(&s->cmdfifo, cmdlen, &n);
>  
>      current_lun = scsi_device_find(&s->bus, 0, s->current_dev->id, lun);
> -- 
> 2.20.1
>