Populate IGMPv3 report checksum

Updates #8346

PiperOrigin-RevId: 501969927

pkg/tcpip/checker/checker.go

@@ -1650,6 +1650,9 @@ func IGMPv3Report(expectedRecords map[tcpip.Address]header.IGMPv3ReportRecordTyp
 		}
 
 		report := header.IGMPv3Report(igmp)
+		if got, want := report.Checksum(), header.IGMPCalculateChecksum(igmp); got != want {
+			t.Errorf("got report.Checksum() = %d, want = %d", got, want)
+		}
 
 		records := report.GroupAddressRecords()
 		for len(expectedRecords) != 0 {

pkg/tcpip/header/igmp_test.go

@@ -336,6 +336,11 @@ func TestIGMPv3Report(t *testing.T) {
 			test.serializer.SerializeInto(b)
 
 			report := header.IGMPv3Report(b)
+
+			if got, want := report.Checksum(), header.IGMPCalculateChecksum(header.IGMP(report)); got != want {
+				t.Errorf("got report.Checksum() = %d, want = %d", got, want)
+			}
+
 			expectedRecords := test.serializer.Records
 
 			records := report.GroupAddressRecords()

pkg/tcpip/header/igmpv3.go

@@ -309,12 +309,13 @@ func (s *IGMPv3ReportSerializer) SerializeInto(b []byte) {
 	b[igmpv3ReportReserved1Offset] = 0
 	binary.BigEndian.PutUint16(b[igmpv3ReportReserved2Offset:], 0)
 	binary.BigEndian.PutUint16(b[igmpv3ReportNumberOfGroupAddressRecordsOffset:], uint16(len(s.Records)))
-	b = b[igmpv3ReportGroupAddressRecordsOffset:]
+	recordsBytes := b[igmpv3ReportGroupAddressRecordsOffset:]
 	for _, record := range s.Records {
 		len := record.Length()
-		record.SerializeInto(b[:len])
-		b = b[len:]
+		record.SerializeInto(recordsBytes[:len])
+		recordsBytes = recordsBytes[len:]
 	}
+	binary.BigEndian.PutUint16(b[igmpChecksumOffset:], IGMPCalculateChecksum(b))
 }
 
 // IGMPv3ReportGroupAddressRecord is an IGMPv3 record.
@@ -436,6 +437,11 @@ func (r IGMPv3ReportGroupAddressRecord) Sources() (AddressIterator, bool) {
 //	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 type IGMPv3Report []byte
 
+// Checksum returns the checksum.
+func (i IGMPv3Report) Checksum() uint16 {
+	return binary.BigEndian.Uint16(i[igmpChecksumOffset:])
+}
+
 // IGMPv3ReportGroupAddressRecordIterator is an iterator over IGMPv3 Multicast
 // Address Records.
 type IGMPv3ReportGroupAddressRecordIterator struct {