diff options
| -rw-r--r-- | pkg/tcpip/transport/tcp/connect.go | 9 | ||||
| -rw-r--r-- | pkg/tcpip/transport/tcp/tcp_test.go | 121 |
2 files changed, 129 insertions, 1 deletions
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go index 00c0c9a92..f14f0ca65 100644 --- a/pkg/tcpip/transport/tcp/connect.go +++ b/pkg/tcpip/transport/tcp/connect.go @@ -299,6 +299,15 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error { return nil } + // RFC 793, Section 3.9, page 69, states that in the SYN-RCVD state, a + // sequence number outside of the window causes an ACK with the proper seq + // number and "After sending the acknowledgment, drop the unacceptable + // segment and return." + if !s.sequenceNumber.InWindow(h.ackNum, h.rcvWnd) { + h.ep.sendRaw(buffer.VectorisedView{}, header.TCPFlagAck, h.iss+1, h.ackNum, h.rcvWnd) + return nil + } + if s.flagIsSet(header.TCPFlagSyn) && s.sequenceNumber != h.ackNum-1 { // We received two SYN segments with different sequence // numbers, so we reset this and restart the whole diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go index 64f765c70..c4b45aa6f 100644 --- a/pkg/tcpip/transport/tcp/tcp_test.go +++ b/pkg/tcpip/transport/tcp/tcp_test.go @@ -4673,7 +4673,7 @@ func TestListenSynRcvdQueueFull(t *testing.T) { SrcPort: context.TestPort, DstPort: context.StackPort, Flags: header.TCPFlagSyn, - SeqNum: seqnum.Value(789), + SeqNum: irs, RcvWnd: 30000, }) @@ -4825,6 +4825,125 @@ func TestListenBacklogFullSynCookieInUse(t *testing.T) { } } +func TestSynRcvdBadSeqNumber(t *testing.T) { + c := context.New(t, defaultMTU) + defer c.Cleanup() + + // Create TCP endpoint. + var err *tcpip.Error + c.EP, err = c.Stack().NewEndpoint(tcp.ProtocolNumber, ipv4.ProtocolNumber, &c.WQ) + if err != nil { + t.Fatalf("NewEndpoint failed: %s", err) + } + + // Bind to wildcard. + if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil { + t.Fatalf("Bind failed: %s", err) + } + + // Start listening. + if err := c.EP.Listen(10); err != nil { + t.Fatalf("Listen failed: %s", err) + } + + // Send a SYN to get a SYN-ACK. This should put the ep into SYN-RCVD state + irs := seqnum.Value(789) + c.SendPacket(nil, &context.Headers{ + SrcPort: context.TestPort, + DstPort: context.StackPort, + Flags: header.TCPFlagSyn, + SeqNum: irs, + RcvWnd: 30000, + }) + + // Receive the SYN-ACK reply. + b := c.GetPacket() + tcpHdr := header.TCP(header.IPv4(b).Payload()) + iss := seqnum.Value(tcpHdr.SequenceNumber()) + tcpCheckers := []checker.TransportChecker{ + checker.SrcPort(context.StackPort), + checker.DstPort(context.TestPort), + checker.TCPFlags(header.TCPFlagAck | header.TCPFlagSyn), + checker.AckNum(uint32(irs) + 1), + } + checker.IPv4(t, b, checker.TCP(tcpCheckers...)) + + // Now send a packet with an out-of-window sequence number + largeSeqnum := irs + seqnum.Value(tcpHdr.WindowSize()) + 1 + c.SendPacket(nil, &context.Headers{ + SrcPort: context.TestPort, + DstPort: context.StackPort, + Flags: header.TCPFlagAck, + SeqNum: largeSeqnum, + AckNum: iss + 1, + RcvWnd: 30000, + }) + + // Should receive an ACK with the expected SEQ number + b = c.GetPacket() + tcpCheckers = []checker.TransportChecker{ + checker.SrcPort(context.StackPort), + checker.DstPort(context.TestPort), + checker.TCPFlags(header.TCPFlagAck), + checker.AckNum(uint32(irs) + 1), + checker.SeqNum(uint32(iss + 1)), + } + checker.IPv4(t, b, checker.TCP(tcpCheckers...)) + + // Now that the socket replied appropriately with the ACK, + // complete the connection to test that the large SEQ num + // did not change the state from SYN-RCVD. + + // Send ACK to move to ESTABLISHED state. + c.SendPacket(nil, &context.Headers{ + SrcPort: context.TestPort, + DstPort: context.StackPort, + Flags: header.TCPFlagAck, + SeqNum: irs + 1, + AckNum: iss + 1, + RcvWnd: 30000, + }) + + newEP, _, err := c.EP.Accept() + + if err != nil && err != tcpip.ErrWouldBlock { + t.Fatalf("Accept failed: %s", err) + } + + if err == tcpip.ErrWouldBlock { + // Try to accept the connections in the backlog. + we, ch := waiter.NewChannelEntry(nil) + c.WQ.EventRegister(&we, waiter.EventIn) + defer c.WQ.EventUnregister(&we) + + // Wait for connection to be established. + select { + case <-ch: + newEP, _, err = c.EP.Accept() + if err != nil { + t.Fatalf("Accept failed: %s", err) + } + + case <-time.After(1 * time.Second): + t.Fatalf("Timed out waiting for accept") + } + } + + // Now verify that the TCP socket is usable and in a connected state. + data := "Don't panic" + _, _, err = newEP.Write(tcpip.SlicePayload(buffer.NewViewFromBytes([]byte(data))), tcpip.WriteOptions{}) + + if err != nil { + t.Fatalf("Write failed: %s", err) + } + + pkt := c.GetPacket() + tcpHdr = header.TCP(header.IPv4(pkt).Payload()) + if string(tcpHdr.Payload()) != data { + t.Fatalf("Unexpected data: got %s, want %s", string(tcpHdr.Payload()), data) + } +} + func TestPassiveConnectionAttemptIncrement(t *testing.T) { c := context.New(t, defaultMTU) defer c.Cleanup() |