Add support for SO_ERROR to packet sockets.

Packet sockets also seem to allow double binding and do not return an error on
linux. This was tested by running the syscall test in a linux namespace as root
and the current test DoubleBind fails@HEAD.

Passes after this change.

Updates #173

PiperOrigin-RevId: 321445137

2 files changed, 42 insertions, 2 deletions

diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index 57b7f5c19..92b487381 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -79,6 +79,11 @@ type endpoint struct {
 	closed        bool
 	stats         tcpip.TransportEndpointStats `state:"nosave"`
 	bound         bool
+	boundNIC      tcpip.NICID
+
+	// lastErrorMu protects lastError.
+	lastErrorMu sync.Mutex   `state:"nosave"`
+	lastError   *tcpip.Error `state:".(string)"`
 }
 
 // NewEndpoint returns a new packet endpoint.
@@ -229,12 +234,14 @@ func (ep *endpoint) Bind(addr tcpip.FullAddress) *tcpip.Error {
 	ep.mu.Lock()
 	defer ep.mu.Unlock()
 
-	if ep.bound {
-		return tcpip.ErrAlreadyBound
+	if ep.bound && ep.boundNIC == addr.NIC {
+		// If the NIC being bound is the same then just return success.
+		return nil
 	}
 
 	// Unregister endpoint with all the nics.
 	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)
+	ep.bound = false
 
 	// Bind endpoint to receive packets from specific interface.
 	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, ep.netProto, ep); err != nil {
@@ -242,6 +249,7 @@ func (ep *endpoint) Bind(addr tcpip.FullAddress) *tcpip.Error {
 	}
 
 	ep.bound = true
+	ep.boundNIC = addr.NIC
 
 	return nil
 }
@@ -336,8 +344,21 @@ func (ep *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 	}
 }
 
+func (ep *endpoint) takeLastError() *tcpip.Error {
+	ep.lastErrorMu.Lock()
+	defer ep.lastErrorMu.Unlock()
+
+	err := ep.lastError
+	ep.lastError = nil
+	return err
+}
+
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (ep *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
+	switch opt.(type) {
+	case tcpip.ErrorOption:
+		return ep.takeLastError()
+	}
 	return tcpip.ErrNotSupported
 }
 
diff --git a/pkg/tcpip/transport/packet/endpoint_state.go b/pkg/tcpip/transport/packet/endpoint_state.go
index 9b88f17e4..e2fa96d17 100644
--- a/pkg/tcpip/transport/packet/endpoint_state.go
+++ b/pkg/tcpip/transport/packet/endpoint_state.go
@@ -15,6 +15,7 @@
 package packet
 
 import (
+	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
@@ -70,3 +71,21 @@ func (ep *endpoint) afterLoad() {
 		panic(*err)
 	}
 }
+
+// saveLastError is invoked by stateify.
+func (ep *endpoint) saveLastError() string {
+	if ep.lastError == nil {
+		return ""
+	}
+
+	return ep.lastError.String()
+}
+
+// loadLastError is invoked by stateify.
+func (ep *endpoint) loadLastError(s string) {
+	if s == "" {
+		return
+	}
+
+	ep.lastError = tcpip.StringToError(s)
+}