[PATCH] acpi: validate hotplug selector on access

[Michael S. Tsirkin]

When bus is looked up on a pci write, we didn't
validate that the lookup succeeded.
Fuzzers thus can trigger QEMU crash by dereferencing the NULL
bus pointer.

Fixes: b32bd763a1 ("pci: introduce acpi-index property for PCI device")
Cc: "Igor Mammedov" <imammedo@redhat.com>
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/770
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/acpi/pcihp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index 30405b5113..a5e182dd3a 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -491,6 +491,9 @@ static void pci_write(void *opaque, hwaddr addr, uint64_t 
data,
         }
 
         bus = acpi_pcihp_find_hotplug_bus(s, s->hotplug_select);
+        if (!bus) {
+            break;
+        }
         QTAILQ_FOREACH_SAFE(kid, &bus->qbus.children, sibling, next) {
             Object *o = OBJECT(kid->child);
             PCIDevice *dev = PCI_DEVICE(o);
-- 
MST