discover: filter packets without correct syntax

Sometimes LLDP packets are sent with "default" port
description field. This allows the listening to continue on
malformed packets.

Signed-off-by: Tuomas Katila <[email protected]>

Author: tkatila

Makefile

@@ -231,7 +231,7 @@ GOLANGCI_LINT = $(LOCALBIN)/golangci-lint-$(GOLANGCI_LINT_VERSION)
 KUSTOMIZE_VERSION ?= v5.3.0
 CONTROLLER_TOOLS_VERSION ?= v0.14.0
 ENVTEST_VERSION ?= release-0.17
-GOLANGCI_LINT_VERSION ?= v1.64.7
+GOLANGCI_LINT_VERSION ?= v1.64.8
 
 .PHONY: kustomize
 kustomize: $(KUSTOMIZE) ## Download kustomize locally if necessary.

cmd/discover/main.go

@@ -95,6 +95,13 @@ func detectLLDP(config *cmdConfig, networkConfigs map[string]*networkConfigurati
 	lldpResultChan := make(chan lldp.DiscoveryResult, len(networkConfigs))
 	timeoutctx, cancelctx := context.WithTimeout(config.ctx, config.timeout)
 
+	filterFunc := func(portDescription string) bool {
+		// Check if the port description field has the correct data in it
+		_, _, err := parseIPFromString(portDescription)
+
+		return err == nil
+	}
+
 	defer cancelctx()
 
 	for _, networkconfig := range networkConfigs {
@@ -107,7 +114,7 @@ func detectLLDP(config *cmdConfig, networkConfigs map[string]*networkConfigurati
 		wg.Add(1)
 		go func() {
 			lldpClient := lldp.NewClient(timeoutctx, networkconfig.link.Attrs().Name, *networkconfig.localHwAddr)
-			if err := lldpClient.Start(lldpResultChan); err != nil {
+			if err := lldpClient.Start(lldpResultChan, filterFunc); err != nil {
 				klog.Infof("Cannot start LLDP client: %v\n", err)
 			}
 			wg.Done()

cmd/discover/network.go

@@ -213,6 +213,15 @@ func getNetworkConfigs(interfaces []string) ([]string, map[string]*networkConfig
 	return allinterfaces, links, nil
 }
 
+func parseIPFromString(portDescription string) (net.IP, *net.IPNet, error) {
+	substrings := strings.Split(portDescription, " ")
+	if len(substrings) < 2 {
+		return nil, nil, fmt.Errorf("port description field doesn't follow expected format (no-alert CIDR)")
+	}
+
+	return net.ParseCIDR(substrings[1])
+}
+
 func selectMask30L3Address(nwconfig *networkConfiguration) (*net.IP, *net.IP, error) {
 	var (
 		peerNetwork *net.IPNet
@@ -221,15 +230,9 @@ func selectMask30L3Address(nwconfig *networkConfiguration) (*net.IP, *net.IP, er
 		err         error
 	)
 
-	substrings := strings.Split(nwconfig.portDescription, " ")
-	if len(substrings) < 2 {
-		return nil, nil, fmt.Errorf("interface '%s' could not split string '%s'",
-			nwconfig.link.Attrs().Name, nwconfig.portDescription)
-	}
-
-	peeraddr, peerNetwork, err = net.ParseCIDR(substrings[1])
+	peeraddr, peerNetwork, err = parseIPFromString(nwconfig.portDescription)
 	if err != nil {
-		return nil, nil, fmt.Errorf("interface '%s' could not parse '%s': %v",
+		return nil, nil, fmt.Errorf("interface '%s' could not parse CIDR from port description '%s': %v",
 			nwconfig.link.Attrs().Name, nwconfig.portDescription, err)
 	}
 

pkg/lldp/client.go

@@ -70,7 +70,7 @@ func NewClient(ctx context.Context, ifacename string, hwAddr []byte) *Client {
 // Start searches on the configured interface for lldp packages and
 // pushes the optional TLV SysName and SysDescription fields of each
 // found lldp package into the given channel.
-func (l *Client) Start(resultChan chan<- DiscoveryResult) error {
+func (l *Client) Start(resultChan chan<- DiscoveryResult, portDescriptionFilter func(string) bool) error {
 	defer l.Close()
 
 	var packetSource *gopacket.PacketSource
@@ -110,6 +110,8 @@ func (l *Client) Start(resultChan chan<- DiscoveryResult) error {
 				continue
 			}
 
+			infoFound := false
+
 			dr := DiscoveryResult{InterfaceName: l.InterfaceName}
 			for _, layer := range packet.Layers() {
 				if layer.LayerType() == layers.LayerTypeLinkLayerDiscovery {
@@ -134,12 +136,26 @@ func (l *Client) Start(resultChan chan<- DiscoveryResult) error {
 					if !ok {
 						continue
 					}
+
+					if portDescriptionFilter != nil && !portDescriptionFilter(info.PortDescription) {
+						// Filter function did not match, ignore this packet
+						continue
+					}
+
 					dr.SysName = info.SysName
 					dr.SysDescription = info.SysDescription
 					dr.PortDescription = info.PortDescription
+
+					infoFound = true
 				}
 
 			}
+
+			if !infoFound {
+				// We did not find the info layer, ignore this packet
+				continue
+			}
+
 			resultChan <- dr
 			return nil