[PULL 07/13] esp: ensure cmdfifo is not empty and current_dev is non-NULL

[Mark Cave-Ayland]

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>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20210407195801.685-7-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 bf22785b79..904fa3179c 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -284,6 +284,9 @@ 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;
+    }
     esp_fifo_pop_buf(&s->cmdfifo, buf, cmdlen);
 
     current_lun = scsi_device_find(&s->bus, 0, s->current_dev->id, lun);
-- 
2.20.1