audit: eliminate potential null pointer deref when auditing macvtap devices

The newly added call to qemuAuditNetDevice in qemuPhysIfaceConnect was
assuming that res_ifname (the name of the macvtap device) was always
valid, but this isn't the case. If openMacvtapTap fails, it always
returns NULL, which would result in a segv.

Since the audit log only needs a record of devices that are actually
sent to qemu, and a failure to open the macvtap device means that no
device will be sent to qemu, we can solve this problem by only doing
the audit if openMacvtapTap is successful (in which case res_ifname is
guaranteed valid).

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 8ca656afee84b12d03263968fc30d317a0332065..72f55d001c56cf5c252d995108885c2b1404e15f 100644 (file)
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -128,8 +128,8 @@ qemuPhysIfaceConnect(virDomainDefPtr def,
                         net->data.direct.mode, vnet_hdr, def->uuid,
                         &net->data.direct.virtPortProfile, &res_ifname,
                         vmop);
-    qemuAuditNetDevice(def, net, res_ifname, rc >= 0);
     if (rc >= 0) {
+        qemuAuditNetDevice(def, net, res_ifname, true);
         VIR_FREE(net->ifname);
         net->ifname = res_ifname;
     }