unix: return ECONNRESET if peer closed with data not read

For SOCK_STREAM type unix socket, we shall return ECONNRESET if peer is
closed with data not read.

We explictly set a flag when closing one end, to differentiate from
just shutdown (where zero shall be returned).

Fixes: #735

Signed-off-by: Jianfeng Tan <henry.tjf@antfin.com>

pkg/sentry/fs/host/socket.go

@@ -385,3 +385,6 @@ func (c *ConnectedEndpoint) RecvMaxQueueSize() int64 {
 func (c *ConnectedEndpoint) Release() {
 	c.ref.DecRefWithDestructor(c.close)
 }
+
+// CloseUnread implements transport.ConnectedEndpoint.CloseUnread.
+func (c *ConnectedEndpoint) CloseUnread() {}

pkg/sentry/socket/unix/transport/connectioned.go

@@ -220,6 +220,11 @@ func (e *connectionedEndpoint) Close() {
 	case e.Connected():
 		e.connected.CloseSend()
 		e.receiver.CloseRecv()
+		// Still have unread data? If yes, we set this into the write
+		// end so that the peer can get ECONNRESET) when it does read.
+		if e.receiver.RecvQueuedSize() > 0 {
+			e.connected.CloseUnread()
+		}
 		c = e.connected
 		r = e.receiver
 		e.connected = nil

pkg/sentry/socket/unix/transport/queue.go

@@ -33,6 +33,7 @@ type queue struct {
 
 	mu       sync.Mutex `state:"nosave"`
 	closed   bool
+	unread   bool
 	used     int64
 	limit    int64
 	dataList messageList
@@ -160,7 +161,9 @@ func (q *queue) Dequeue() (e *message, notify bool, err *syserr.Error) {
 	if q.dataList.Front() == nil {
 		err := syserr.ErrWouldBlock
 		if q.closed {
-			err = syserr.ErrClosedForReceive
+			if err = syserr.ErrClosedForReceive; q.unread {
+				err = syserr.ErrConnectionReset
+			}
 		}
 		q.mu.Unlock()
 
@@ -188,7 +191,9 @@ func (q *queue) Peek() (*message, *syserr.Error) {
 	if q.dataList.Front() == nil {
 		err := syserr.ErrWouldBlock
 		if q.closed {
-			err = syserr.ErrClosedForReceive
+			if err = syserr.ErrClosedForReceive; q.unread {
+				err = syserr.ErrConnectionReset
+			}
 		}
 		return nil, err
 	}
@@ -208,3 +213,11 @@ func (q *queue) QueuedSize() int64 {
 func (q *queue) MaxQueueSize() int64 {
 	return q.limit
 }
+
+// CloseUnread sets flag to indicate that the peer is closed (not shutdown)
+// with unread data. So if read on this queue shall return ECONNRESET error.
+func (q *queue) CloseUnread() {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	q.unread = true
+}

pkg/sentry/socket/unix/transport/unix.go

@@ -604,6 +604,10 @@ type ConnectedEndpoint interface {
 	// Release releases any resources owned by the ConnectedEndpoint. It should
 	// be called before droping all references to a ConnectedEndpoint.
 	Release()
+
+	// CloseUnread sets the fact that this end is closed with unread data to
+	// the peer socket.
+	CloseUnread()
 }
 
 // +stateify savable
@@ -707,6 +711,11 @@ func (e *connectedEndpoint) Release() {
 	e.writeQueue.DecRef()
 }
 
+// CloseUnread implements ConnectedEndpoint.CloseUnread.
+func (e *connectedEndpoint) CloseUnread() {
+	e.writeQueue.CloseUnread()
+}
+
 // baseEndpoint is an embeddable unix endpoint base used in both the connected and connectionless
 // unix domain socket Endpoint implementations.
 //

test/syscalls/linux/socket_unix_stream.cc

@@ -14,6 +14,7 @@
 
 #include <stdio.h>
 #include <sys/un.h>
+#include <poll.h>
 #include "gtest/gtest.h"
 #include "gtest/gtest.h"
 #include "test/syscalls/linux/socket_test_util.h"
@@ -70,6 +71,25 @@ TEST_P(StreamUnixSocketPairTest, RecvmsgOneSideClosed) {
               SyscallSucceedsWithValue(0));
 }
 
+TEST_P(StreamUnixSocketPairTest, ReadOneSideClosedWithUnreadData) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  char buf[10] = {};
+  ASSERT_THAT(RetryEINTR(write)(sockets->second_fd(), buf, sizeof(buf)),
+              SyscallSucceedsWithValue(sizeof(buf)));
+
+  ASSERT_THAT(shutdown(sockets->first_fd(), SHUT_RDWR),
+              SyscallSucceeds());
+
+  ASSERT_THAT(RetryEINTR(read)(sockets->second_fd(), buf, sizeof(buf)),
+              SyscallSucceedsWithValue(0));
+
+  ASSERT_THAT(close(sockets->release_first_fd()), SyscallSucceeds());
+
+  ASSERT_THAT(RetryEINTR(read)(sockets->second_fd(), buf, sizeof(buf)),
+              SyscallFailsWithErrno(ECONNRESET));
+}
+
 INSTANTIATE_TEST_SUITE_P(
     AllUnixDomainSockets, StreamUnixSocketPairTest,
     ::testing::ValuesIn(IncludeReversals(VecCat<SocketPairKind>(