Return proper exit code for exec errors

Exec erros from the exec() syscall in the container's init should be
treated as if the container ran but couldn't execute the process for the
user instead of returning a libcontainer error as if it was an issue in
the library.

Before specifying different commands like `/etc`, `asldfkjasdlfj`, or
`/alsdjfkasdlfj` would always return 1 on the command line with a
libcontainer specific error message.  Now they return the correct
message and exit status defined for unix processes.

Example:

```bash
root@deathstar:/containers/redis# runc start test
exec: "/asdlfkjasldkfj": file does not exist
root@deathstar:/containers/redis# echo $?
127
root@deathstar:/containers/redis# runc start test
exec: "asdlfkjasldkfj": executable file not found in $PATH
root@deathstar:/containers/redis# echo $?
127
root@deathstar:/containers/redis# runc start test
exec: "/etc": permission denied
root@deathstar:/containers/redis# echo $?
126
```

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

libcontainer/factory_linux.go

@@ -227,32 +227,40 @@ func (l *LinuxFactory) StartInitialization() (err error) {
 		pipe = os.NewFile(uintptr(pipefd), "pipe")
 		it   = initType(os.Getenv("_LIBCONTAINER_INITTYPE"))
 	)
+	defer pipe.Close()
 	// clear the current process's environment to clean any libcontainer
 	// specific env vars.
 	os.Clearenv()
-	var i initer
-	defer func() {
-		// We have an error during the initialization of the container's init,
-		// send it back to the parent process in the form of an initError.
-		// If container's init successed, syscall.Exec will not return, hence
-		// this defer function will never be called.
+	i, err := newContainerInit(it, pipe)
+	if err != nil {
+		l.sendError(nil, pipe, err)
+		return err
+	}
+	if err := i.Init(); err != nil {
+		if !isExecError(err) {
+			l.sendError(i, pipe, err)
+		}
+		return err
+	}
+	return nil
+}
+
+func (l *LinuxFactory) sendError(i initer, pipe *os.File, err error) {
+	// We have an error during the initialization of the container's init,
+	// send it back to the parent process in the form of an initError.
+	// If container's init successed, syscall.Exec will not return, hence
+	// this defer function will never be called.
+	if i != nil {
 		if _, ok := i.(*linuxStandardInit); ok {
 			//  Synchronisation only necessary for standard init.
 			if err := utils.WriteJSON(pipe, syncT{procError}); err != nil {
 				panic(err)
 			}
 		}
-		if err := utils.WriteJSON(pipe, newSystemError(err)); err != nil {
-			panic(err)
-		}
-		// ensure that this pipe is always closed
-		pipe.Close()
-	}()
-	i, err = newContainerInit(it, pipe)
-	if err != nil {
-		return err
 	}
-	return i.Init()
+	if err := utils.WriteJSON(pipe, newSystemError(err)); err != nil {
+		panic(err)
+	}
 }
 
 func (l *LinuxFactory) loadState(root string) (*State, error) {
@@ -280,3 +288,8 @@ func (l *LinuxFactory) validateID(id string) error {
 	}
 	return nil
 }
+
+func isExecError(err error) bool {
+	_, ok := err.(*exec.Error)
+	return ok
+}

libcontainer/integration/execin_test.go

@@ -4,8 +4,10 @@ import (
 	"bytes"
 	"io"
 	"os"
+	"os/exec"
 	"strconv"
 	"strings"
+	"syscall"
 	"testing"
 	"time"
 
@@ -138,25 +140,27 @@ func TestExecInError(t *testing.T) {
 	}()
 	ok(t, err)
 
-	for i := 0; i < 42; i++ {
-		var out bytes.Buffer
-		unexistent := &libcontainer.Process{
-			Cwd:    "/",
-			Args:   []string{"unexistent"},
-			Env:    standardEnvironment,
-			Stdout: &out,
-		}
-		err = container.Start(unexistent)
-		if err == nil {
-			t.Fatal("Should be an error")
-		}
-		if !strings.Contains(err.Error(), "executable file not found") {
-			t.Fatalf("Should be error about not found executable, got %s", err)
-		}
-		if !bytes.Contains(out.Bytes(), []byte("executable file not found")) {
-			t.Fatalf("executable file not found error not delivered to stdio:\n%s", out.String())
+	var out bytes.Buffer
+	unexistent := &libcontainer.Process{
+		Cwd:    "/",
+		Args:   []string{"unexistent"},
+		Env:    standardEnvironment,
+		Stdout: &out,
+		Stderr: &out,
+	}
+	err = container.Start(unexistent)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ws, err := unexistent.Wait()
+	if err != nil {
+		if _, ok := err.(*exec.ExitError); !ok {
+			t.Fatal(err)
 		}
 	}
+	if s := ws.Sys().(syscall.WaitStatus).ExitStatus(); s != 127 {
+		t.Fatalf("expected wait status of 127 but received %d", s)
+	}
 }
 
 func TestExecInTTY(t *testing.T) {

libcontainer/integration/init_test.go

@@ -1,8 +1,11 @@
 package integration
 
 import (
+	"fmt"
 	"os"
+	"os/exec"
 	"runtime"
+	"strconv"
 	"testing"
 
 	"github.com/Sirupsen/logrus"
@@ -24,8 +27,25 @@ func init() {
 		logrus.Fatalf("unable to initialize for container: %s", err)
 	}
 	if err := factory.StartInitialization(); err != nil {
+		// return proper unix error codes
+		if exerr, ok := err.(*exec.Error); ok {
+			switch exerr.Err {
+			case os.ErrPermission:
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(126)
+			case exec.ErrNotFound:
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(127)
+			default:
+				if os.IsNotExist(exerr.Err) {
+					fmt.Fprintf(os.Stderr, "exec: %s: %v\n", strconv.Quote(exerr.Name), os.ErrNotExist)
+					os.Exit(127)
+				}
+			}
+		}
 		logrus.Fatal(err)
 	}
+	panic("init: init failed to start contianer")
 }
 
 var (

start.go

@@ -84,7 +84,7 @@ func init() {
 		if err := factory.StartInitialization(); err != nil {
 			fatal(err)
 		}
-		panic("--this line should have never been executed, congratulations--")
+		panic("libcontainer: container init failed to exec")
 	}
 }
 

utils.go

@@ -6,7 +6,9 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"strconv"
 	"syscall"
 
 	"github.com/Sirupsen/logrus"
@@ -161,6 +163,22 @@ func getContainer(context *cli.Context) (libcontainer.Container, error) {
 // fatal prints the error's details if it is a libcontainer specific error type
 // then exits the program with an exit status of 1.
 func fatal(err error) {
+	// return proper unix error codes
+	if exerr, ok := err.(*exec.Error); ok {
+		switch exerr.Err {
+		case os.ErrPermission:
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(126)
+		case exec.ErrNotFound:
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(127)
+		default:
+			if os.IsNotExist(exerr.Err) {
+				fmt.Fprintf(os.Stderr, "exec: %s: %v\n", strconv.Quote(exerr.Name), os.ErrNotExist)
+				os.Exit(127)
+			}
+		}
+	}
 	if lerr, ok := err.(libcontainer.Error); ok {
 		lerr.Detail(os.Stderr)
 		os.Exit(1)