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&gt; 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&gt; > --- > 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?