Read _LIBCONTAINER_INITPID in nsexec.c

This fixes ExtraFiles for execin
Thanks @Mic95 for report

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

integration/execin_test.go

@@ -314,3 +314,78 @@ func TestExecInEnvironment(t *testing.T) {
 		t.Fatalf("unexpected running process, output %q", out)
 	}
 }
+
+func TestExecinPassExtraFiles(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+	rootfs, err := newRootfs()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer remove(rootfs)
+	config := newTemplateConfig(rootfs)
+	container, err := newContainer(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer container.Destroy()
+
+	// Execute a first process in the container
+	stdinR, stdinW, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	process := &libcontainer.Process{
+		Args:  []string{"cat"},
+		Env:   standardEnvironment,
+		Stdin: stdinR,
+	}
+	err = container.Start(process)
+	stdinR.Close()
+	defer stdinW.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var stdout bytes.Buffer
+	pipeout1, pipein1, err := os.Pipe()
+	pipeout2, pipein2, err := os.Pipe()
+	inprocess := &libcontainer.Process{
+		Args:       []string{"sh", "-c", "cd /proc/$$/fd; echo -n *; echo -n 1 >3; echo -n 2 >4"},
+		Env:        []string{"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"},
+		ExtraFiles: []*os.File{pipein1, pipein2},
+		Stdin:      nil,
+		Stdout:     &stdout,
+	}
+	err = container.Start(inprocess)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	waitProcess(inprocess, t)
+
+	out := string(stdout.Bytes())
+	// fd 5 is the directory handle for /proc/$$/fd
+	if out != "0 1 2 3 4 5" {
+		t.Fatalf("expected to have the file descriptors '0 1 2 3 4 5' passed to exec, got '%s'", out)
+	}
+	var buf = []byte{0}
+	_, err = pipeout1.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out1 := string(buf)
+	if out1 != "1" {
+		t.Fatalf("expected first pipe to receive '1', got '%s'", out1)
+	}
+
+	_, err = pipeout2.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out2 := string(buf)
+	if out2 != "2" {
+		t.Fatalf("expected second pipe to receive '2', got '%s'", out2)
+	}
+}

nsenter/nsenter_test.go

@@ -24,7 +24,7 @@ func TestNsenterAlivePid(t *testing.T) {
 		Path:       os.Args[0],
 		Args:       args,
 		ExtraFiles: []*os.File{w},
-		Env:        []string{fmt.Sprintf("_LIBCONTAINER_INITPID=%d", os.Getpid())},
+		Env:        []string{fmt.Sprintf("_LIBCONTAINER_INITPID=%d", os.Getpid()), "_LIBCONTAINER_INITPIPE=3"},
 	}
 
 	if err := cmd.Start(); err != nil {

nsenter/nsexec.c

@@ -66,7 +66,7 @@ void nsexec()
 	const int num = sizeof(namespaces) / sizeof(char *);
 	jmp_buf env;
 	char buf[PATH_MAX], *val;
-	int i, tfd, child, len, consolefd = -1;
+	int i, tfd, child, len, pipenum, consolefd = -1;
 	pid_t pid;
 	char *console;
 
@@ -81,6 +81,19 @@ void nsexec()
 		exit(1);
 	}
 
+	val = getenv("_LIBCONTAINER_INITPIPE");
+	if (val == NULL) {
+		pr_perror("Child pipe not found");
+		exit(1);
+	}
+
+	pipenum = atoi(val);
+	snprintf(buf, sizeof(buf), "%d", pipenum);
+	if (strcmp(val, buf)) {
+		pr_perror("Unable to parse _LIBCONTAINER_INITPIPE");
+		exit(1);
+	}
+
 	console = getenv("_LIBCONTAINER_CONSOLE_PATH");
 	if (console != NULL) {
 		consolefd = open(console, O_RDWR);
@@ -158,7 +171,7 @@ void nsexec()
 
 	len = snprintf(buf, sizeof(buf), "{ \"pid\" : %d }\n", child);
 
-	if (write(3, buf, len) != len) {
+	if (write(pipenum, buf, len) != len) {
 		pr_perror("Unable to send a child pid");
 		kill(child, SIGKILL);
 		exit(1);