Use spec with clean paths for gofer

Otherwise the gofer's attach point may be different from sandbox when there
symlinks in the path.

PiperOrigin-RevId: 219730492
Change-Id: Ia9c4c2d16228c6a1a9e790e0cb673fd881003fe1

5 files changed, 52 insertions, 21 deletions

diff --git a/runsc/boot/loader_test.go b/runsc/boot/loader_test.go
index c342ee005..d5cee5608 100644
--- a/runsc/boot/loader_test.go
+++ b/runsc/boot/loader_test.go
@@ -77,8 +77,11 @@ func startGofer(root string) (int, func(), error) {
 		syscall.Close(goferEnd)
 		return 0, nil, fmt.Errorf("error creating server on FD %d: %v", goferEnd, err)
 	}
+	at, err := fsgofer.NewAttachPoint(root, fsgofer.Config{ROMount: true})
+	if err != nil {
+		return 0, nil, err
+	}
 	go func() {
-		at := fsgofer.NewAttachPoint(root, fsgofer.Config{ROMount: true})
 		s := p9.NewServer(at)
 		if err := s.Handle(socket); err != nil {
 			log.Infof("Gofer is stopping. FD: %d, err: %v\n", goferEnd, err)
diff --git a/runsc/cmd/gofer.go b/runsc/cmd/gofer.go
index 7cc666e10..4ec3dba9c 100644
--- a/runsc/cmd/gofer.go
+++ b/runsc/cmd/gofer.go
@@ -99,7 +99,12 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		panic("unreachable")
 	}
 
-	spec, err := specutils.ReadSpec(g.bundleDir)
+	specFile, err := specutils.OpenCleanSpec(g.bundleDir)
+	if err != nil {
+		Fatalf("error opening spec: %v", err)
+	}
+	spec, err := specutils.ReadSpecFromFile(g.bundleDir, specFile)
+	specFile.Close()
 	if err != nil {
 		Fatalf("error reading spec: %v", err)
 	}
@@ -121,10 +126,14 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 
 	// Start with root mount, then add any other additional mount as needed.
 	ats := make([]p9.Attacher, 0, len(spec.Mounts)+1)
-	ats = append(ats, fsgofer.NewAttachPoint("/", fsgofer.Config{
+	ap, err := fsgofer.NewAttachPoint("/", fsgofer.Config{
 		ROMount:      spec.Root.Readonly,
 		PanicOnWrite: g.panicOnWrite,
-	}))
+	})
+	if err != nil {
+		Fatalf("Error creating attach point: %v", err)
+	}
+	ats = append(ats, ap)
 	log.Infof("Serving %q mapped to %q on FD %d (ro: %t)", "/", root, g.ioFDs[0], spec.Root.Readonly)
 
 	mountIdx := 1 // first one is the root
@@ -134,7 +143,11 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 				ROMount:      isReadonlyMount(m.Options),
 				PanicOnWrite: g.panicOnWrite,
 			}
-			ats = append(ats, fsgofer.NewAttachPoint(m.Destination, cfg))
+			ap, err := fsgofer.NewAttachPoint(m.Destination, cfg)
+			if err != nil {
+				Fatalf("Error creating attach point: %v", err)
+			}
+			ats = append(ats, ap)
 
 			if mountIdx >= len(g.ioFDs) {
 				Fatalf("No FD found for mount. Did you forget --io-fd? mount: %d, %v", len(g.ioFDs), m)
diff --git a/runsc/container/container.go b/runsc/container/container.go
index 9da25a863..4c542ccb9 100644
--- a/runsc/container/container.go
+++ b/runsc/container/container.go
@@ -374,6 +374,9 @@ func (c *Container) Start(conf *boot.Config) error {
 			return fmt.Errorf("setup mounts: %v", err)
 		}
 		c.Spec.Mounts = cleanMounts
+		if err := specutils.WriteCleanSpec(c.BundleDir, c.Spec); err != nil {
+			return fmt.Errorf("writing clean spec: %v", err)
+		}
 
 		// Create the gofer process.
 		ioFiles, err := c.createGoferProcess(c.Spec, conf, c.BundleDir)
diff --git a/runsc/fsgofer/fsgofer.go b/runsc/fsgofer/fsgofer.go
index 4412d7e2f..b5746447f 100644
--- a/runsc/fsgofer/fsgofer.go
+++ b/runsc/fsgofer/fsgofer.go
@@ -26,6 +26,7 @@ import (
 	"math"
 	"os"
 	"path"
+	"path/filepath"
 	"sync"
 	"syscall"
 
@@ -99,24 +100,28 @@ type attachPoint struct {
 }
 
 // NewAttachPoint creates a new attacher that gives local file
-// access to all files under 'prefix'.
-func NewAttachPoint(prefix string, c Config) p9.Attacher {
+// access to all files under 'prefix'. 'prefix' must be an absolute path.
+func NewAttachPoint(prefix string, c Config) (p9.Attacher, error) {
+	// Sanity check the prefix.
+	if !filepath.IsAbs(prefix) {
+		return nil, fmt.Errorf("attach point prefix must be absolute %q", prefix)
+	}
 	return &attachPoint{
 		prefix:  prefix,
 		conf:    c,
 		devices: make(map[uint64]uint8),
-	}
+	}, nil
 }
 
 // Attach implements p9.Attacher.
 func (a *attachPoint) Attach() (p9.File, error) {
-	// Sanity check the prefix.
-	fi, err := os.Stat(a.prefix)
+	// dirFD (1st argument) is ignored because 'prefix' is always absolute.
+	stat, err := statAt(-1, a.prefix)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("stat file %q, err: %v", a.prefix, err)
 	}
 	mode := os.O_RDWR
-	if a.conf.ROMount || fi.IsDir() {
+	if a.conf.ROMount || stat.Mode&syscall.S_IFDIR != 0 {
 		mode = os.O_RDONLY
 	}
 
@@ -125,11 +130,6 @@ func (a *attachPoint) Attach() (p9.File, error) {
 	if err != nil {
 		return nil, fmt.Errorf("unable to open file %q, err: %v", a.prefix, err)
 	}
-	stat, err := stat(int(f.Fd()))
-	if err != nil {
-		f.Close()
-		return nil, fmt.Errorf("failed to stat file %q, err: %v", a.prefix, err)
-	}
 
 	a.attachedMu.Lock()
 	defer a.attachedMu.Unlock()
diff --git a/runsc/fsgofer/fsgofer_test.go b/runsc/fsgofer/fsgofer_test.go
index f799b1e25..47b5380dc 100644
--- a/runsc/fsgofer/fsgofer_test.go
+++ b/runsc/fsgofer/fsgofer_test.go
@@ -80,7 +80,10 @@ func runCustom(t *testing.T, types []fileType, confs []Config, test func(*testin
 			}
 			defer os.RemoveAll(path)
 
-			a := NewAttachPoint(path, c)
+			a, err := NewAttachPoint(path, c)
+			if err != nil {
+				t.Fatalf("NewAttachPoint failed: %v", err)
+			}
 			root, err := a.Attach()
 			if err != nil {
 				t.Fatalf("Attach failed, err: %v", err)
@@ -107,7 +110,10 @@ func setup(ft fileType) (string, string, error) {
 	}
 
 	// First attach with writable configuration to setup tree.
-	a := NewAttachPoint(path, Config{})
+	a, err := NewAttachPoint(path, Config{})
+	if err != nil {
+		return "", "", err
+	}
 	root, err := a.Attach()
 	if err != nil {
 		return "", "", fmt.Errorf("Attach failed, err: %v", err)
@@ -556,7 +562,10 @@ func TestAttachFile(t *testing.T) {
 		t.Fatalf("os.Create(%q) failed, err: %v", path, err)
 	}
 
-	a := NewAttachPoint(path, conf)
+	a, err := NewAttachPoint(path, conf)
+	if err != nil {
+		t.Fatalf("NewAttachPoint failed: %v", err)
+	}
 	root, err := a.Attach()
 	if err != nil {
 		t.Fatalf("Attach failed, err: %v", err)
@@ -595,7 +604,10 @@ func TestDoubleAttachError(t *testing.T) {
 		t.Fatalf("ioutil.TempDir() failed, err: %v", err)
 	}
 	defer os.RemoveAll(root)
-	a := NewAttachPoint(root, conf)
+	a, err := NewAttachPoint(root, conf)
+	if err != nil {
+		t.Fatalf("NewAttachPoint failed: %v", err)
+	}
 
 	if _, err := a.Attach(); err != nil {
 		t.Fatalf("Attach failed: %v", err)