Re: [libvirt] [Qemu-devel] [PATCH v3 1/6] pc: fix possible NULL pointer dereference in pc_machine_get_device_memory_region_size()
Igor Mammedov <imammedo(a)redhat.com> writes:
QEMU will crash when device-memory-region-size property is read if
ms->device_memory
wasn't initialized yet (ex: property being inspected during preconfig time).
Reproduced:
$ qemu-system-x86_64 -nodefaults -S -display none -preconfig -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 50,
"minor": 0, "major": 4}, "package":
"v4.0.0-828-ga7b21f6762"}, "capabilities": ["oob"]}}
{"execute": "qmp_capabilities"}
{"return": {}}
{"execute": "qom-get", "arguments": {"path":
"/machine", "property": "device-memory-region-size"}}
Segmentation fault (core dumped)
First time I started looking at this series, I went "I'll need a
reproducer to fully understand what's up, and I don't feel like finding
one now; next series, please". Second time, I had to spend a few
minutes on the reproducer. Wasn't hard, since you provided a clue.
Still: make review easy, include a reproducer whenever you can.
Instead of crashing return 0 if ms->device_memory hasn't been
initialized.
Signed-off-by: Igor Mammedov <imammedo(a)redhat.com>
---
hw/i386/pc.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index d98b737..de91e90 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2461,7 +2461,11 @@ pc_machine_get_device_memory_region_size(Object *obj, Visitor *v,
Error **errp)
{
MachineState *ms = MACHINE(obj);
- int64_t value = memory_region_size(&ms->device_memory->mr);
+ int64_t value = 0;
+
+ if (ms->device_memory) {
+ memory_region_size(&ms->device_memory->mr);
+ }
visit_type_int(v, name, &value, errp);
}
This makes qom-get return 0 for the size of memory that doesn't exist,
yet.
A possible alternative would be setting an error.
Opinions?