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-rw-r--r--pkg/tcpip/transport/tcp/accept.go30
-rw-r--r--pkg/tcpip/transport/tcp/connect.go19
-rw-r--r--pkg/tcpip/transport/tcp/tcp_test.go138
3 files changed, 176 insertions, 11 deletions
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index e9c5099ea..0802e984e 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -143,6 +143,15 @@ func decSynRcvdCount() {
synRcvdCount.Unlock()
}
+// synCookiesInUse() returns true if the synRcvdCount is greater than
+// SynRcvdCountThreshold.
+func synCookiesInUse() bool {
+ synRcvdCount.Lock()
+ v := synRcvdCount.value
+ synRcvdCount.Unlock()
+ return v >= SynRcvdCountThreshold
+}
+
// newListenContext creates a new listen context.
func newListenContext(stk *stack.Stack, listenEP *endpoint, rcvWnd seqnum.Size, v6only bool, netProto tcpip.NetworkProtocolNumber) *listenContext {
l := &listenContext{
@@ -446,6 +455,27 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
return
}
+ if !synCookiesInUse() {
+ // Send a reset as this is an ACK for which there is no
+ // half open connections and we are not using cookies
+ // yet.
+ //
+ // The only time we should reach here when a connection
+ // was opened and closed really quickly and a delayed
+ // ACK was received from the sender.
+ replyWithReset(s)
+ return
+ }
+
+ // Since SYN cookies are in use this is potentially an ACK to a
+ // SYN-ACK we sent but don't have a half open connection state
+ // as cookies are being used to protect against a potential SYN
+ // flood. In such cases validate the cookie and if valid create
+ // a fully connected endpoint and deliver to the accept queue.
+ //
+ // If not, silently drop the ACK to avoid leaking information
+ // when under a potential syn flood attack.
+ //
// Validate the cookie.
data, ok := ctx.isCookieValid(s.id, s.ackNumber-1, s.sequenceNumber-1)
if !ok || int(data) >= len(mssTable) {
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 00d2ae524..21038a65a 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -720,13 +720,18 @@ func (e *endpoint) handleClose() *tcpip.Error {
return nil
}
-// resetConnectionLocked sends a RST segment and puts the endpoint in an error
-// state with the given error code. This method must only be called from the
-// protocol goroutine.
+// resetConnectionLocked puts the endpoint in an error state with the given
+// error code and sends a RST if and only if the error is not ErrConnectionReset
+// indicating that the connection is being reset due to receiving a RST. This
+// method must only be called from the protocol goroutine.
func (e *endpoint) resetConnectionLocked(err *tcpip.Error) {
- e.sendRaw(buffer.VectorisedView{}, header.TCPFlagAck|header.TCPFlagRst, e.snd.sndUna, e.rcv.rcvNxt, 0)
+ // Only send a reset if the connection is being aborted for a reason
+ // other than receiving a reset.
e.state = StateError
e.hardError = err
+ if err != tcpip.ErrConnectionReset {
+ e.sendRaw(buffer.VectorisedView{}, header.TCPFlagAck|header.TCPFlagRst, e.snd.sndUna, e.rcv.rcvNxt, 0)
+ }
}
// completeWorkerLocked is called by the worker goroutine when it's about to
@@ -806,7 +811,7 @@ func (e *endpoint) keepaliveTimerExpired() *tcpip.Error {
if e.keepalive.unacked >= e.keepalive.count {
e.keepalive.Unlock()
- return tcpip.ErrConnectionReset
+ return tcpip.ErrTimeout
}
// RFC1122 4.2.3.6: TCP keepalive is a dataless ACK with
@@ -1068,6 +1073,10 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
e.workMu.Lock()
if err := funcs[v].f(); err != nil {
e.mu.Lock()
+ // Ensure we release all endpoint registration and route
+ // references as the connection is now in an error
+ // state.
+ e.workerCleanup = true
e.resetConnectionLocked(err)
// Lock released below.
epilogue()
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index f79b8ec5f..32bb45224 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -190,21 +190,146 @@ func TestTCPResetsSentIncrement(t *testing.T) {
}
}
+// TestTCPResetSentForACKWhenNotUsingSynCookies checks that the stack generates
+// a RST if an ACK is received on the listening socket for which there is no
+// active handshake in progress and we are not using SYN cookies.
+func TestTCPResetSentForACKWhenNotUsingSynCookies(t *testing.T) {
+ c := context.New(t, defaultMTU)
+ defer c.Cleanup()
+
+ wq := &waiter.Queue{}
+ ep, err := c.Stack().NewEndpoint(tcp.ProtocolNumber, ipv4.ProtocolNumber, wq)
+ if err != nil {
+ t.Fatalf("NewEndpoint failed: %v", err)
+ }
+ if err := ep.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
+ t.Fatalf("Bind failed: %v", err)
+ }
+
+ if err := ep.Listen(10); err != nil {
+ t.Fatalf("Listen failed: %v", err)
+ }
+
+ // Send a SYN request.
+ iss := seqnum.Value(789)
+ c.SendPacket(nil, &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: context.StackPort,
+ Flags: header.TCPFlagSyn,
+ SeqNum: iss,
+ })
+
+ // Receive the SYN-ACK reply.
+ b := c.GetPacket()
+ tcpHdr := header.TCP(header.IPv4(b).Payload())
+ c.IRS = seqnum.Value(tcpHdr.SequenceNumber())
+
+ ackHeaders := &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: context.StackPort,
+ Flags: header.TCPFlagAck,
+ SeqNum: iss + 1,
+ AckNum: c.IRS + 1,
+ }
+
+ // Send ACK.
+ c.SendPacket(nil, ackHeaders)
+
+ // Try to accept the connection.
+ we, ch := waiter.NewChannelEntry(nil)
+ wq.EventRegister(&we, waiter.EventIn)
+ defer wq.EventUnregister(&we)
+
+ c.EP, _, err = ep.Accept()
+ if err == tcpip.ErrWouldBlock {
+ // Wait for connection to be established.
+ select {
+ case <-ch:
+ c.EP, _, err = ep.Accept()
+ if err != nil {
+ t.Fatalf("Accept failed: %v", err)
+ }
+
+ case <-time.After(1 * time.Second):
+ t.Fatalf("Timed out waiting for accept")
+ }
+ }
+
+ c.EP.Close()
+ checker.IPv4(t, c.GetPacket(), checker.TCP(
+ checker.SrcPort(context.StackPort),
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS+1)),
+ checker.AckNum(uint32(iss)+1),
+ checker.TCPFlags(header.TCPFlagFin|header.TCPFlagAck)))
+
+ finHeaders := &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: context.StackPort,
+ Flags: header.TCPFlagAck | header.TCPFlagFin,
+ SeqNum: iss + 1,
+ AckNum: c.IRS + 2,
+ }
+
+ c.SendPacket(nil, finHeaders)
+
+ // Get the ACK to the FIN we just sent.
+ c.GetPacket()
+
+ // Now resend the same ACK, this ACK should generate a RST as there
+ // should be no endpoint in SYN-RCVD state and we are not using
+ // syn-cookies yet. The reason we send the same ACK is we need a valid
+ // cookie(IRS) generated by the netstack without which the ACK will be
+ // rejected.
+ c.SendPacket(nil, ackHeaders)
+
+ checker.IPv4(t, c.GetPacket(), checker.TCP(
+ checker.SrcPort(context.StackPort),
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS+1)),
+ checker.AckNum(uint32(iss)+1),
+ checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck)))
+}
+
func TestTCPResetsReceivedIncrement(t *testing.T) {
c := context.New(t, defaultMTU)
defer c.Cleanup()
stats := c.Stack().Stats()
want := stats.TCP.ResetsReceived.Value() + 1
- ackNum := seqnum.Value(789)
+ iss := seqnum.Value(789)
rcvWnd := seqnum.Size(30000)
- c.CreateConnected(ackNum, rcvWnd, nil)
+ c.CreateConnected(iss, rcvWnd, nil)
c.SendPacket(nil, &context.Headers{
SrcPort: context.TestPort,
DstPort: c.Port,
- SeqNum: c.IRS.Add(2),
- AckNum: ackNum.Add(2),
+ SeqNum: iss.Add(1),
+ AckNum: c.IRS.Add(1),
+ RcvWnd: rcvWnd,
+ Flags: header.TCPFlagRst,
+ })
+
+ if got := stats.TCP.ResetsReceived.Value(); got != want {
+ t.Errorf("got stats.TCP.ResetsReceived.Value() = %v, want = %v", got, want)
+ }
+}
+
+func TestTCPResetsDoNotGenerateResets(t *testing.T) {
+ c := context.New(t, defaultMTU)
+ defer c.Cleanup()
+
+ stats := c.Stack().Stats()
+ want := stats.TCP.ResetsReceived.Value() + 1
+ iss := seqnum.Value(789)
+ rcvWnd := seqnum.Size(30000)
+ c.CreateConnected(iss, rcvWnd, nil)
+
+ c.SendPacket(nil, &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: c.Port,
+ SeqNum: iss.Add(1),
+ AckNum: c.IRS.Add(1),
RcvWnd: rcvWnd,
Flags: header.TCPFlagRst,
})
@@ -212,6 +337,7 @@ func TestTCPResetsReceivedIncrement(t *testing.T) {
if got := stats.TCP.ResetsReceived.Value(); got != want {
t.Errorf("got stats.TCP.ResetsReceived.Value() = %v, want = %v", got, want)
}
+ c.CheckNoPacketTimeout("got an unexpected packet", 100*time.Millisecond)
}
func TestActiveHandshake(t *testing.T) {
@@ -3459,8 +3585,8 @@ func TestKeepalive(t *testing.T) {
),
)
- if _, _, err := c.EP.Read(nil); err != tcpip.ErrConnectionReset {
- t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrConnectionReset)
+ if _, _, err := c.EP.Read(nil); err != tcpip.ErrTimeout {
+ t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrTimeout)
}
}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-19 10:11:20 +0000