Save shutdown flags first.

With rpcinet if shutdown flags are not saved before making
the rpc a race is possible where blocked threads are woken
up before the flags have been persisted. This would mean
that threads can block indefinitely in a recvmsg after a
shutdown(SHUT_RD) has happened.

PiperOrigin-RevId: 223089783
Change-Id: If595e7add12aece54bcdf668ab64c570910d061a

1 files changed, 7 insertions, 4 deletions

diff --git a/pkg/sentry/socket/rpcinet/socket.go b/pkg/sentry/socket/rpcinet/socket.go
index 788d853c9..7328661ab 100644
--- a/pkg/sentry/socket/rpcinet/socket.go
+++ b/pkg/sentry/socket/rpcinet/socket.go
@@ -354,6 +354,13 @@ func (s *socketOperations) Listen(t *kernel.Task, backlog int) *syserr.Error {
 
 // Shutdown implements socket.Socket.Shutdown.
 func (s *socketOperations) Shutdown(t *kernel.Task, how int) *syserr.Error {
+	// We save the shutdown state because of strange differences on linux
+	// related to recvs on blocking vs. non-blocking sockets after a SHUT_RD.
+	// We need to emulate that behavior on the blocking side.
+	// TODO: There is a possible race that can exist with loopback,
+	// where data could possibly be lost.
+	s.setShutdownFlags(how)
+
 	stack := t.NetworkContext().(*Stack)
 	id, c := stack.rpcConn.NewRequest(pb.SyscallRequest{Args: &pb.SyscallRequest_Shutdown{&pb.ShutdownRequest{Fd: s.fd, How: int64(how)}}}, false /* ignoreResult */)
 	<-c
@@ -362,10 +369,6 @@ func (s *socketOperations) Shutdown(t *kernel.Task, how int) *syserr.Error {
 		return syserr.FromHost(syscall.Errno(e))
 	}
 
-	// We save the shutdown state because of strange differences on linux
-	// related to recvs on blocking vs. non-blocking sockets after a SHUT_RD.
-	// We need to emulate that behavior on the blocking side.
-	s.setShutdownFlags(how)
 	return nil
 }