Stub support for TCP_SYNCNT and TCP_WINDOW_CLAMP.

This change adds support for TCP_SYNCNT and TCP_WINDOW_CLAMP options
in GetSockOpt/SetSockOpt. This change does not really change any
behaviour in Netstack and only stores/returns the stored value.

Actual honoring of these options will be added as required.

Fixes #2626, #2625

PiperOrigin-RevId: 311453777

1 files changed, 21 insertions, 0 deletions

diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index cfd9a4e8e..1e64283b5 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -64,6 +64,10 @@ const (
 	// DefaultTCPTimeWaitTimeout is the amount of time that sockets linger
 	// in TIME_WAIT state before being marked closed.
 	DefaultTCPTimeWaitTimeout = 60 * time.Second
+
+	// DefaultSynRetries is the default value for the number of SYN retransmits
+	// before a connect is aborted.
+	DefaultSynRetries = 6
 )
 
 // SACKEnabled option can be used to enable SACK support in the TCP
@@ -164,6 +168,7 @@ type protocol struct {
 	tcpTimeWaitTimeout         time.Duration
 	minRTO                     time.Duration
 	synRcvdCount               synRcvdCounter
+	synRetries                 uint8
 	dispatcher                 *dispatcher
 }
 
@@ -346,6 +351,15 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 		p.mu.Unlock()
 		return nil
 
+	case tcpip.TCPSynRetriesOption:
+		if v < 1 || v > 255 {
+			return tcpip.ErrInvalidOptionValue
+		}
+		p.mu.Lock()
+		p.synRetries = uint8(v)
+		p.mu.Unlock()
+		return nil
+
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
@@ -420,6 +434,12 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 		p.mu.RUnlock()
 		return nil
 
+	case *tcpip.TCPSynRetriesOption:
+		p.mu.RLock()
+		*v = tcpip.TCPSynRetriesOption(p.synRetries)
+		p.mu.RUnlock()
+		return nil
+
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
@@ -452,6 +472,7 @@ func NewProtocol() stack.TransportProtocol {
 		tcpTimeWaitTimeout:         DefaultTCPTimeWaitTimeout,
 		synRcvdCount:               synRcvdCounter{threshold: SynRcvdCountThreshold},
 		dispatcher:                 newDispatcher(runtime.GOMAXPROCS(0)),
+		synRetries:                 DefaultSynRetries,
 		minRTO:                     MinRTO,
 	}
 }