lldp: Fix for OVS crashes when a LLDP-enabled port is deleted

Issue:
When LLDP is enabled on a port, a structure to hold LLDP related state
is created and that structure has a reference to the port. The ofproto
monitor thread accesses the LLDP structure to periodically send packets
over the associated port. When the port is deleted, the LLDP structure
is not cleaned up and it continues to refer to the deleted port.

When the monitor thread attempts to access the deleted port OVS crashes.
Crash can happen with bridge delete and bond delete also.

Fix:
Remove all references to the LLDP structure and free it when
the port is deleted.

Signed-off-by: Surya Rudra <rudrasurya.r@altencalsoftlabs.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

ofproto/ofproto-dpif.c

@@ -2239,24 +2239,24 @@ set_lldp(struct ofport *ofport_,
          const struct smap *cfg)
 {
     struct ofport_dpif *ofport = ofport_dpif_cast(ofport_);
+    struct ofproto_dpif *ofproto = ofproto_dpif_cast(ofport->up.ofproto);
     int error = 0;
 
     if (cfg) {
         if (!ofport->lldp) {
-            struct ofproto_dpif *ofproto;
-
-            ofproto = ofproto_dpif_cast(ofport->up.ofproto);
             ofproto->backer->need_revalidate = REV_RECONFIGURE;
             ofport->lldp = lldp_create(ofport->up.netdev, ofport_->mtu, cfg);
         }
 
         if (!lldp_configure(ofport->lldp, cfg)) {
+            lldp_unref(ofport->lldp);
+            ofport->lldp = NULL;
             error = EINVAL;
         }
-    }
-    if (error) {
+    } else if (ofport->lldp) {
         lldp_unref(ofport->lldp);
         ofport->lldp = NULL;
+        ofproto->backer->need_revalidate = REV_RECONFIGURE;
     }
 
     ofproto_dpif_monitor_port_update(ofport,

ofproto/ofproto.c

@@ -2492,6 +2492,9 @@ ofproto_port_unregister(struct ofproto *ofproto, ofp_port_t ofp_port)
 {
     struct ofport *port = ofproto_get_port(ofproto, ofp_port);
     if (port) {
+        if (port->ofproto->ofproto_class->set_lldp) {
+            port->ofproto->ofproto_class->set_lldp(port, NULL);
+        }
         if (port->ofproto->ofproto_class->set_stp_port) {
             port->ofproto->ofproto_class->set_stp_port(port, NULL);
         }