Fix Accept to not return error for sockets in accept queue.

Accept on gVisor will return an error if a socket in the accept queue was closed
before Accept() was called. Linux will return the new fd even if the returned
socket is already closed by the peer say due to a RST being sent by the peer.

This seems to be intentional in linux more details on the github issue.

Fixes #3780

PiperOrigin-RevId: 329828404

pkg/sentry/socket/netstack/netstack.go

@@ -830,7 +830,7 @@ func (s *socketOpsCommon) Listen(t *kernel.Task, backlog int) *syserr.Error {
 
 // blockingAccept implements a blocking version of accept(2), that is, if no
 // connections are ready to be accept, it will block until one becomes ready.
-func (s *socketOpsCommon) blockingAccept(t *kernel.Task) (tcpip.Endpoint, *waiter.Queue, *syserr.Error) {
+func (s *socketOpsCommon) blockingAccept(t *kernel.Task, peerAddr *tcpip.FullAddress) (tcpip.Endpoint, *waiter.Queue, *syserr.Error) {
 	// Register for notifications.
 	e, ch := waiter.NewChannelEntry(nil)
 	s.EventRegister(&e, waiter.EventIn)
@@ -839,7 +839,7 @@ func (s *socketOpsCommon) blockingAccept(t *kernel.Task) (tcpip.Endpoint, *waite
 	// Try to accept the connection again; if it fails, then wait until we
 	// get a notification.
 	for {
-		if ep, wq, err := s.Endpoint.Accept(); err != tcpip.ErrWouldBlock {
+		if ep, wq, err := s.Endpoint.Accept(peerAddr); err != tcpip.ErrWouldBlock {
 			return ep, wq, syserr.TranslateNetstackError(err)
 		}
 
@@ -852,15 +852,18 @@ func (s *socketOpsCommon) blockingAccept(t *kernel.Task) (tcpip.Endpoint, *waite
 // Accept implements the linux syscall accept(2) for sockets backed by
 // tcpip.Endpoint.
 func (s *SocketOperations) Accept(t *kernel.Task, peerRequested bool, flags int, blocking bool) (int32, linux.SockAddr, uint32, *syserr.Error) {
-	// Issue the accept request to get the new endpoint.
-	ep, wq, terr := s.Endpoint.Accept()
+	var peerAddr *tcpip.FullAddress
+	if peerRequested {
+		peerAddr = &tcpip.FullAddress{}
+	}
+	ep, wq, terr := s.Endpoint.Accept(peerAddr)
 	if terr != nil {
 		if terr != tcpip.ErrWouldBlock || !blocking {
 			return 0, nil, 0, syserr.TranslateNetstackError(terr)
 		}
 
 		var err *syserr.Error
-		ep, wq, err = s.blockingAccept(t)
+		ep, wq, err = s.blockingAccept(t, peerAddr)
 		if err != nil {
 			return 0, nil, 0, err
 		}
@@ -880,13 +883,8 @@ func (s *SocketOperations) Accept(t *kernel.Task, peerRequested bool, flags int,
 
 	var addr linux.SockAddr
 	var addrLen uint32
-	if peerRequested {
-		// Get address of the peer and write it to peer slice.
-		var err *syserr.Error
-		addr, addrLen, err = ns.FileOperations.(*SocketOperations).GetPeerName(t)
-		if err != nil {
-			return 0, nil, 0, err
-		}
+	if peerAddr != nil {
+		addr, addrLen = ConvertAddress(s.family, *peerAddr)
 	}
 
 	fd, e := t.NewFDFrom(0, ns, kernel.FDFlags{

pkg/sentry/socket/netstack/netstack_vfs2.go

@@ -151,14 +151,18 @@ func (s *SocketVFS2) Write(ctx context.Context, src usermem.IOSequence, opts vfs
 // tcpip.Endpoint.
 func (s *SocketVFS2) Accept(t *kernel.Task, peerRequested bool, flags int, blocking bool) (int32, linux.SockAddr, uint32, *syserr.Error) {
 	// Issue the accept request to get the new endpoint.
-	ep, wq, terr := s.Endpoint.Accept()
+	var peerAddr *tcpip.FullAddress
+	if peerRequested {
+		peerAddr = &tcpip.FullAddress{}
+	}
+	ep, wq, terr := s.Endpoint.Accept(peerAddr)
 	if terr != nil {
 		if terr != tcpip.ErrWouldBlock || !blocking {
 			return 0, nil, 0, syserr.TranslateNetstackError(terr)
 		}
 
 		var err *syserr.Error
-		ep, wq, err = s.blockingAccept(t)
+		ep, wq, err = s.blockingAccept(t, peerAddr)
 		if err != nil {
 			return 0, nil, 0, err
 		}
@@ -176,13 +180,9 @@ func (s *SocketVFS2) Accept(t *kernel.Task, peerRequested bool, flags int, block
 
 	var addr linux.SockAddr
 	var addrLen uint32
-	if peerRequested {
+	if peerAddr != nil {
 		// Get address of the peer and write it to peer slice.
-		var err *syserr.Error
-		addr, addrLen, err = ns.Impl().(*SocketVFS2).GetPeerName(t)
-		if err != nil {
-			return 0, nil, 0, err
-		}
+		addr, addrLen = ConvertAddress(s.family, *peerAddr)
 	}
 
 	fd, e := t.NewFDFromVFS2(0, ns, kernel.FDFlags{