syz-fuzzer: fix gvisor testing

Testing code wasn't ready to dial stdin.
Make it use the same logic rpc package uses
to connecto to host.

3 files changed, 34 insertions, 15 deletions

diff --git a/pkg/instance/instance.go b/pkg/instance/instance.go
index 2849098ac..f804b2724 100644
--- a/pkg/instance/instance.go
+++ b/pkg/instance/instance.go
@@ -8,6 +8,7 @@ package instance
 import (
 	"bytes"
 	"fmt"
+	"io/ioutil"
 	"net"
 	"os"
 	"path/filepath"
@@ -214,10 +215,21 @@ func (inst *inst) testInstance() error {
 	acceptErr := make(chan error, 1)
 	go func() {
 		conn, err := ln.Accept()
-		if err == nil {
-			conn.Close()
+		if err != nil {
+			acceptErr <- err
+			return
 		}
-		acceptErr <- err
+		defer conn.Close()
+		data, err := ioutil.ReadAll(conn)
+		if err != nil {
+			acceptErr <- err
+			return
+		}
+		if string(data) != "HELLO" {
+			acceptErr <- fmt.Errorf("received bad handshake from VM: %q", string(data))
+			return
+		}
+		acceptErr <- nil
 	}()
 	fwdAddr, err := inst.vm.Forward(ln.Addr().(*net.TCPAddr).Port)
 	if err != nil {
diff --git a/pkg/rpctype/rpc.go b/pkg/rpctype/rpc.go
index 6d9048077..3838855a4 100644
--- a/pkg/rpctype/rpc.go
+++ b/pkg/rpctype/rpc.go
@@ -56,20 +56,25 @@ type RPCClient struct {
 	c    *rpc.Client
 }
 
-func NewRPCClient(addr string) (*RPCClient, error) {
+func Dial(addr string) (net.Conn, error) {
 	var conn net.Conn
 	var err error
 	if addr == "stdin" {
 		// This is used by vm/gvisor which passes us a unix socket connection in stdin.
-		if conn, err = net.FileConn(os.Stdin); err != nil {
-			return nil, err
-		}
-	} else {
-		if conn, err = net.DialTimeout("tcp", addr, 60*time.Second); err != nil {
-			return nil, err
-		}
-		conn.(*net.TCPConn).SetKeepAlive(true)
-		conn.(*net.TCPConn).SetKeepAlivePeriod(time.Minute)
+		return net.FileConn(os.Stdin)
+	}
+	if conn, err = net.DialTimeout("tcp", addr, 60*time.Second); err != nil {
+		return nil, err
+	}
+	conn.(*net.TCPConn).SetKeepAlive(true)
+	conn.(*net.TCPConn).SetKeepAlivePeriod(time.Minute)
+	return conn, nil
+}
+
+func NewRPCClient(addr string) (*RPCClient, error) {
+	conn, err := Dial(addr)
+	if err != nil {
+		return nil, err
 	}
 	cli := &RPCClient{
 		conn: conn,
diff --git a/syz-fuzzer/testing.go b/syz-fuzzer/testing.go
index f5f3158ab..7b544ee35 100644
--- a/syz-fuzzer/testing.go
+++ b/syz-fuzzer/testing.go
@@ -5,7 +5,6 @@ package main
 
 import (
 	"fmt"
-	"net"
 	"strings"
 	"time"
 
@@ -30,10 +29,13 @@ type checkArgs struct {
 
 func testImage(hostAddr string, args *checkArgs) {
 	log.Logf(0, "connecting to host at %v", hostAddr)
-	conn, err := net.Dial("tcp", hostAddr)
+	conn, err := rpctype.Dial(hostAddr)
 	if err != nil {
 		log.Fatalf("failed to connect: %v", err)
 	}
+	if _, err := conn.Write([]byte("HELLO")); err != nil {
+		log.Fatalf("failed to write to host: %v", err)
+	}
 	conn.Close()
 	if _, err := checkMachine(args); err != nil {
 		log.Fatalf("%v", err)