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

5 files changed, 39 insertions, 28 deletions

diff --git a/pkg/sentry/socket/unix/transport/connectioned.go b/pkg/sentry/socket/unix/transport/connectioned.go
index e3a75b519..aa4f3c04d 100644
--- a/pkg/sentry/socket/unix/transport/connectioned.go
+++ b/pkg/sentry/socket/unix/transport/connectioned.go
@@ -391,7 +391,7 @@ func (e *connectionedEndpoint) Listen(backlog int) *syserr.Error {
 }
 
 // Accept accepts a new connection.
-func (e *connectionedEndpoint) Accept() (Endpoint, *syserr.Error) {
+func (e *connectionedEndpoint) Accept(peerAddr *tcpip.FullAddress) (Endpoint, *syserr.Error) {
 	e.Lock()
 	defer e.Unlock()
 
@@ -401,6 +401,18 @@ func (e *connectionedEndpoint) Accept() (Endpoint, *syserr.Error) {
 
 	select {
 	case ne := <-e.acceptedChan:
+		if peerAddr != nil {
+			ne.Lock()
+			c := ne.connected
+			ne.Unlock()
+			if c != nil {
+				addr, err := c.GetLocalAddress()
+				if err != nil {
+					return nil, syserr.TranslateNetstackError(err)
+				}
+				*peerAddr = addr
+			}
+		}
 		return ne, nil
 
 	default:
diff --git a/pkg/sentry/socket/unix/transport/connectionless.go b/pkg/sentry/socket/unix/transport/connectionless.go
index 4751b2fd8..f8aacca13 100644
--- a/pkg/sentry/socket/unix/transport/connectionless.go
+++ b/pkg/sentry/socket/unix/transport/connectionless.go
@@ -144,12 +144,12 @@ func (e *connectionlessEndpoint) Connect(ctx context.Context, server BoundEndpoi
 }
 
 // Listen starts listening on the connection.
-func (e *connectionlessEndpoint) Listen(int) *syserr.Error {
+func (*connectionlessEndpoint) Listen(int) *syserr.Error {
 	return syserr.ErrNotSupported
 }
 
 // Accept accepts a new connection.
-func (e *connectionlessEndpoint) Accept() (Endpoint, *syserr.Error) {
+func (*connectionlessEndpoint) Accept(*tcpip.FullAddress) (Endpoint, *syserr.Error) {
 	return nil, syserr.ErrNotSupported
 }
 
diff --git a/pkg/sentry/socket/unix/transport/unix.go b/pkg/sentry/socket/unix/transport/unix.go
index 1200cf9bb..cbbdd000f 100644
--- a/pkg/sentry/socket/unix/transport/unix.go
+++ b/pkg/sentry/socket/unix/transport/unix.go
@@ -151,7 +151,10 @@ type Endpoint interface {
 	// block if no new connections are available.
 	//
 	// The returned Queue is the wait queue for the newly created endpoint.
-	Accept() (Endpoint, *syserr.Error)
+	//
+	// peerAddr if not nil will be populated with the address of the connected
+	// peer on a successful accept.
+	Accept(peerAddr *tcpip.FullAddress) (Endpoint, *syserr.Error)
 
 	// Bind binds the endpoint to a specific local address and port.
 	// Specifying a NIC is optional.
diff --git a/pkg/sentry/socket/unix/unix.go b/pkg/sentry/socket/unix/unix.go
index 0a7a26495..616530eb6 100644
--- a/pkg/sentry/socket/unix/unix.go
+++ b/pkg/sentry/socket/unix/unix.go
@@ -205,7 +205,7 @@ 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 *SocketOperations) blockingAccept(t *kernel.Task) (transport.Endpoint, *syserr.Error) {
+func (s *SocketOperations) blockingAccept(t *kernel.Task, peerAddr *tcpip.FullAddress) (transport.Endpoint, *syserr.Error) {
 	// Register for notifications.
 	e, ch := waiter.NewChannelEntry(nil)
 	s.EventRegister(&e, waiter.EventIn)
@@ -214,7 +214,7 @@ func (s *SocketOperations) blockingAccept(t *kernel.Task) (transport.Endpoint, *
 	// Try to accept the connection; if it fails, then wait until we get a
 	// notification.
 	for {
-		if ep, err := s.ep.Accept(); err != syserr.ErrWouldBlock {
+		if ep, err := s.ep.Accept(peerAddr); err != syserr.ErrWouldBlock {
 			return ep, err
 		}
 
@@ -227,15 +227,18 @@ func (s *SocketOperations) blockingAccept(t *kernel.Task) (transport.Endpoint, *
 // Accept implements the linux syscall accept(2) for sockets backed by
 // a transport.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, err := s.ep.Accept()
+	var peerAddr *tcpip.FullAddress
+	if peerRequested {
+		peerAddr = &tcpip.FullAddress{}
+	}
+	ep, err := s.ep.Accept(peerAddr)
 	if err != nil {
 		if err != syserr.ErrWouldBlock || !blocking {
 			return 0, nil, 0, err
 		}
 
 		var err *syserr.Error
-		ep, err = s.blockingAccept(t)
+		ep, err = s.blockingAccept(t, peerAddr)
 		if err != nil {
 			return 0, nil, 0, err
 		}
@@ -252,13 +255,8 @@ 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.
-		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 = netstack.ConvertAddress(linux.AF_UNIX, *peerAddr)
 	}
 
 	fd, e := t.NewFDFrom(0, ns, kernel.FDFlags{
diff --git a/pkg/sentry/socket/unix/unix_vfs2.go b/pkg/sentry/socket/unix/unix_vfs2.go
index 65a285b8f..e25c7e84a 100644
--- a/pkg/sentry/socket/unix/unix_vfs2.go
+++ b/pkg/sentry/socket/unix/unix_vfs2.go
@@ -96,7 +96,7 @@ func (s *SocketVFS2) GetSockOpt(t *kernel.Task, level, name int, outPtr usermem.
 
 // 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 *SocketVFS2) blockingAccept(t *kernel.Task) (transport.Endpoint, *syserr.Error) {
+func (s *SocketVFS2) blockingAccept(t *kernel.Task, peerAddr *tcpip.FullAddress) (transport.Endpoint, *syserr.Error) {
 	// Register for notifications.
 	e, ch := waiter.NewChannelEntry(nil)
 	s.socketOpsCommon.EventRegister(&e, waiter.EventIn)
@@ -105,7 +105,7 @@ func (s *SocketVFS2) blockingAccept(t *kernel.Task) (transport.Endpoint, *syserr
 	// Try to accept the connection; if it fails, then wait until we get a
 	// notification.
 	for {
-		if ep, err := s.ep.Accept(); err != syserr.ErrWouldBlock {
+		if ep, err := s.ep.Accept(peerAddr); err != syserr.ErrWouldBlock {
 			return ep, err
 		}
 
@@ -118,15 +118,18 @@ func (s *SocketVFS2) blockingAccept(t *kernel.Task) (transport.Endpoint, *syserr
 // Accept implements the linux syscall accept(2) for sockets backed by
 // a transport.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, err := s.ep.Accept()
+	var peerAddr *tcpip.FullAddress
+	if peerRequested {
+		peerAddr = &tcpip.FullAddress{}
+	}
+	ep, err := s.ep.Accept(peerAddr)
 	if err != nil {
 		if err != syserr.ErrWouldBlock || !blocking {
 			return 0, nil, 0, err
 		}
 
 		var err *syserr.Error
-		ep, err = s.blockingAccept(t)
+		ep, err = s.blockingAccept(t, peerAddr)
 		if err != nil {
 			return 0, nil, 0, err
 		}
@@ -144,13 +147,8 @@ func (s *SocketVFS2) Accept(t *kernel.Task, peerRequested bool, flags int, block
 
 	var addr linux.SockAddr
 	var addrLen uint32
-	if peerRequested {
-		// Get address of the peer.
-		var err *syserr.Error
-		addr, addrLen, err = ns.Impl().(*SocketVFS2).GetPeerName(t)
-		if err != nil {
-			return 0, nil, 0, err
-		}
+	if peerAddr != nil {
+		addr, addrLen = netstack.ConvertAddress(linux.AF_UNIX, *peerAddr)
 	}
 
 	fd, e := t.NewFDFromVFS2(0, ns, kernel.FDFlags{