fix(tarfs): follow hardlinks in ReadFile

Signed-off-by: Brad Lugo <[email protected]>

go.mod

@@ -55,6 +55,7 @@ require (
 	github.com/prometheus/common v0.48.0 // indirect
 	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
 	go.opentelemetry.io/otel/metric v1.24.0 // indirect
 	golang.org/x/mod v0.16.0 // indirect
 	google.golang.org/protobuf v1.33.0 // indirect

go.sum

@@ -172,13 +172,17 @@ github.com/sirupsen/logrus v1.4.1/go.mod h1:ni0Sbl8bgC9z8RoU9G6nDWqqs/fq4eDPysMB
 github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/objx v0.2.0 h1:Hbg2NidpLE8veEBkEZTL3CvlkUIVzuU9jDplZO54c48=
 github.com/stretchr/objx v0.2.0/go.mod h1:qt09Ya8vawLte6SNmTgCsAVtYtaKzEcn8ATUoHMkEqE=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
 github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
 github.com/ulikunitz/xz v0.5.11 h1:kpFauv27b6ynzBNT/Xy+1k+fK4WswhN/6PN5WhFAGw8=

pkg/tarfs/tarfs.go

@@ -457,10 +457,28 @@ func (f *FS) ReadFile(name string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	if i.h.FileInfo().Mode().Type()&fs.ModeSymlink != 0 {
+
+	typ := i.h.FileInfo().Mode().Type()
+	var r *tar.Reader
+	switch {
+	case typ.IsRegular() && i.h.Typeflag != tar.TypeLink:
+		r = tar.NewReader(io.NewSectionReader(f.r, i.off, i.sz))
+	case typ.IsRegular() && i.h.Typeflag == tar.TypeLink:
+		tgt, err := f.getInode(op, i.h.Linkname)
+		if err != nil {
+			return nil, err
+		}
+		r = tar.NewReader(io.NewSectionReader(f.r, tgt.off, tgt.sz))
+	case typ&fs.ModeSymlink != 0: // typ.IsSymlink()
 		return f.ReadFile(i.h.Linkname)
+	default:
+		// Pretend all other kinds of files don't exist.
+		return nil, &fs.PathError{
+			Op:   op,
+			Path: name,
+			Err:  fs.ErrExist,
+		}
 	}
-	r := tar.NewReader(io.NewSectionReader(f.r, i.off, i.sz))
 	if _, err := r.Next(); err != nil {
 		return nil, &fs.PathError{
 			Op:   op,

pkg/tarfs/tarfs_test.go

@@ -460,6 +460,83 @@ func TestSymlinks(t *testing.T) {
 	}))
 }
 
+func TestReadFile(t *testing.T) {
+	type tarfsFile struct {
+		Header tar.Header
+		Data   []byte
+	}
+
+	tmp := t.TempDir()
+	setupAndRun := func(openErr bool, tarfsFiles []tarfsFile, chk func(*testing.T, *FS)) {
+		t.Helper()
+		// This is a perfect candidate for using test.GenerateFixture, but
+		// creates an import cycle.
+		f, err := os.Create(filepath.Join(tmp, path.Base(t.Name())))
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer f.Close()
+
+		tw := tar.NewWriter(f)
+		for _, tarfsFile := range tarfsFiles {
+			h := tarfsFile.Header
+			h.Size = int64(len(tarfsFile.Data))
+			h.Format = tar.FormatGNU
+			if err := tw.WriteHeader(&h); err != nil {
+				t.Error(err)
+			}
+			_, err := tw.Write(tarfsFile.Data)
+			if err != nil {
+				t.Error(err)
+			}
+		}
+		if err := tw.Close(); err != nil {
+			t.Error(err)
+		}
+
+		sys, err := New(f)
+		t.Log(err)
+		if (err != nil) != openErr {
+			t.Fail()
+		}
+
+		if chk != nil {
+			chk(t, sys)
+		}
+	}
+
+	t.Run("Hardlink", func(t *testing.T) {
+		originalData := []byte(`Hello, World!`)
+		abData := make([]byte, len(originalData))
+		copy(abData, originalData)
+
+		setupAndRun(false, []tarfsFile{
+			{
+				Header: tar.Header{Name: `a/`},
+			},
+			{
+				Header: tar.Header{Name: `a/b`},
+				Data:   abData,
+			},
+			{
+				Header: tar.Header{
+					Name:     `a/c`,
+					Typeflag: tar.TypeLink,
+					Linkname: `a/b`,
+				},
+			},
+		}, func(t *testing.T, sys *FS) {
+			acFile, err := sys.ReadFile("a/c")
+			if err != nil {
+				t.Errorf("error while opening file: %v", err)
+			}
+			if !bytes.Equal(originalData, acFile) {
+				t.Errorf("unexpected \"%s\", got \"%s\"", originalData, acFile)
+			}
+		})
+	})
+}
+
 func TestKnownLayers(t *testing.T) {
 	ents, err := os.ReadDir(`testdata/known`)
 	if err != nil {