api: disallow virConnect*HypervisorCPU on read-only connections

These APIs can be used to execute arbitrary emulators.
Forbid them on read-only connections.

Fixes: CVE-2019-10168
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit bf6c2830)
Signed-off-by: NJán Tomko <jtomko@redhat.com>

src/libvirt-host.c

@@ -1041,6 +1041,7 @@ virConnectCompareHypervisorCPU(virConnectPtr conn,
 
     virCheckConnectReturn(conn, VIR_CPU_COMPARE_ERROR);
     virCheckNonNullArgGoto(xmlCPU, error);
+    virCheckReadOnlyGoto(conn->flags, error);
 
     if (conn->driver->connectCompareHypervisorCPU) {
         int ret;
@@ -1234,6 +1235,7 @@ virConnectBaselineHypervisorCPU(virConnectPtr conn,
 
     virCheckConnectReturn(conn, NULL);
     virCheckNonNullArgGoto(xmlCPUs, error);
+    virCheckReadOnlyGoto(conn->flags, error);
 
     if (conn->driver->connectBaselineHypervisorCPU) {
         char *cpu;