sandbox: place files with content

Signed-off-by: Ophestra <cat@gensokyo.uk>

sandbox/container_test.go

@@ -88,7 +88,8 @@ func TestContainer(t *testing.T) {
 				Tmpfs("/tmp", 0, 0755).
 				Bind(os.Args[0], os.Args[0], 0).
 				Mkdir("/usr/bin").
-				Link(os.Args[0], "/usr/bin/sandbox.test")
+				Link(os.Args[0], "/usr/bin/sandbox.test").
+				Place("/etc/hostname", []byte(container.Args[5]))
 			// in case test has cgo enabled
 			var libPaths []string
 			if entries, err := ldd.ExecFilter(ctx,
@@ -109,7 +110,9 @@ func TestContainer(t *testing.T) {
 			mnt = append(mnt, tc.mnt...)
 			mnt = append(mnt,
 				&check.Mntent{FSName: "tmpfs", Dir: "/tmp", Type: "tmpfs", Opts: "host_passthrough"},
-				&check.Mntent{FSName: "\x00", Dir: os.Args[0], Type: "\x00", Opts: "\x00"})
+				&check.Mntent{FSName: "\x00", Dir: os.Args[0], Type: "\x00", Opts: "\x00"},
+				&check.Mntent{FSName: "rootfs", Dir: "/etc/hostname", Type: "tmpfs", Opts: "host_passthrough"},
+			)
 			for _, name := range libPaths {
 				mnt = append(mnt, &check.Mntent{FSName: "\x00", Dir: name, Type: "\x00", Opts: "\x00", Freq: -1, Passno: -1})
 			}
@@ -175,6 +178,12 @@ func TestHelperCheckContainer(t *testing.T) {
 		} else if name != os.Args[5] {
 			t.Errorf("Hostname: %q, want %q", name, os.Args[5])
 		}
+
+		if p, err := os.ReadFile("/etc/hostname"); err != nil {
+			t.Fatalf("%v", err)
+		} else if string(p) != os.Args[5] {
+			t.Errorf("/etc/hostname: %q, want %q", string(p), os.Args[5])
+		}
 	})
 	t.Run("seccomp", func(t *testing.T) { check.MustAssertSeccomp() })
 	t.Run("mntent", func(t *testing.T) { check.MustAssertMounts("", "/proc/mounts", "/proc/self/fd/0") })

sandbox/sequential.go

@@ -6,6 +6,7 @@ import (
 	"math"
 	"os"
 	"path"
+	"slices"
 	"syscall"
 	"unsafe"
 )
@@ -262,3 +263,55 @@ func (f *Ops) Mkdir(dest string) *Ops {
 	*f = append(*f, Mkdir(dest))
 	return f
 }
+
+func init() { gob.Register(new(Tmpfile)) }
+
+// Tmpfile places a file in container Path containing Data.
+type Tmpfile struct {
+	Path string
+	Data []byte
+}
+
+func (t *Tmpfile) apply(*Params) error {
+	if !path.IsAbs(t.Path) {
+		return msg.WrapErr(syscall.EBADE,
+			fmt.Sprintf("path %q is not absolute", t.Path))
+	}
+
+	var tmpPath string
+	if f, err := os.CreateTemp("/", "tmp.*"); err != nil {
+		return msg.WrapErr(err, err.Error())
+	} else if _, err = f.Write(t.Data); err != nil {
+		return wrapErrSuffix(err,
+			"cannot write to intermediate file:")
+	} else if err = f.Close(); err != nil {
+		return wrapErrSuffix(err,
+			"cannot close intermediate file:")
+	} else {
+		tmpPath = f.Name()
+	}
+
+	if err := bindMount(tmpPath, t.Path, BindSource|bindAbsolute); err != nil {
+		return err
+	} else if err = os.Remove(tmpPath); err != nil {
+		return msg.WrapErr(err, err.Error())
+	}
+	return nil
+}
+
+func (t *Tmpfile) Is(op Op) bool {
+	vt, ok := op.(*Tmpfile)
+	return ok && t.Path == vt.Path && slices.Equal(t.Data, vt.Data)
+}
+func (*Tmpfile) prefix() string { return "placing" }
+func (t *Tmpfile) String() string {
+	return fmt.Sprintf("tmpfile %q (%d bytes)", t.Path, len(t.Data))
+}
+func (f *Ops) Place(name string, data []byte) *Ops { *f = append(*f, &Tmpfile{name, data}); return f }
+func (f *Ops) PlaceP(name string, dataP **[]byte) *Ops {
+	t := &Tmpfile{Path: name}
+	*dataP = &t.Data
+
+	*f = append(*f, t)
+	return f
+}