Revert "Pass root to chroot to for chroot Untar"

This reverts commit 9781cceb09.

Signed-off-by: Tibor Vass <tibor@docker.com>

daemon/archive.go

@@ -31,12 +31,11 @@ type archiver interface {
 }
 
 // helper functions to extract or archive
-func extractArchive(i interface{}, src io.Reader, dst string, opts *archive.TarOptions, root string) error {
+func extractArchive(i interface{}, src io.Reader, dst string, opts *archive.TarOptions) error {
 	if ea, ok := i.(extractor); ok {
 		return ea.ExtractArchive(src, dst, opts)
 	}
-
-	return chrootarchive.UntarWithRoot(src, dst, opts, root)
+	return chrootarchive.Untar(src, dst, opts)
 }
 
 func archivePath(i interface{}, src string, opts *archive.TarOptions) (io.ReadCloser, error) {
@@ -368,7 +367,7 @@ func (daemon *Daemon) containerExtractToDir(container *container.Container, path
 		}
 	}
 
-	if err := extractArchive(driver, content, resolvedPath, options, container.BaseFS.Path()); err != nil {
+	if err := extractArchive(driver, content, resolvedPath, options); err != nil {
 		return err
 	}
 

pkg/chrootarchive/archive.go

@@ -27,34 +27,18 @@ func NewArchiver(idMapping *idtools.IdentityMapping) *archive.Archiver {
 // The archive may be compressed with one of the following algorithms:
 //  identity (uncompressed), gzip, bzip2, xz.
 func Untar(tarArchive io.Reader, dest string, options *archive.TarOptions) error {
-	return untarHandler(tarArchive, dest, options, true, dest)
-}
-
-// UntarWithRoot is the same as `Untar`, but allows you to pass in a root directory
-// The root directory is the directory that will be chrooted to.
-// `dest` must be a path within `root`, if it is not an error will be returned.
-//
-// `root` should set to a directory which is not controlled by any potentially
-// malicious process.
-//
-// This should be used to prevent a potential attacker from manipulating `dest`
-// such that it would provide access to files outside of `dest` through things
-// like symlinks. Normally `ResolveSymlinksInScope` would handle this, however
-// sanitizing symlinks in this manner is inherrently racey:
-// ref: CVE-2018-15664
-func UntarWithRoot(tarArchive io.Reader, dest string, options *archive.TarOptions, root string) error {
-	return untarHandler(tarArchive, dest, options, true, root)
+	return untarHandler(tarArchive, dest, options, true)
 }
 
 // UntarUncompressed reads a stream of bytes from `archive`, parses it as a tar archive,
 // and unpacks it into the directory at `dest`.
 // The archive must be an uncompressed stream.
 func UntarUncompressed(tarArchive io.Reader, dest string, options *archive.TarOptions) error {
-	return untarHandler(tarArchive, dest, options, false, dest)
+	return untarHandler(tarArchive, dest, options, false)
 }
 
 // Handler for teasing out the automatic decompression
-func untarHandler(tarArchive io.Reader, dest string, options *archive.TarOptions, decompress bool, root string) error {
+func untarHandler(tarArchive io.Reader, dest string, options *archive.TarOptions, decompress bool) error {
 	if tarArchive == nil {
 		return fmt.Errorf("Empty archive")
 	}
@@ -85,5 +69,5 @@ func untarHandler(tarArchive io.Reader, dest string, options *archive.TarOptions
 		r = decompressedArchive
 	}
 
-	return invokeUnpack(r, dest, options, root)
+	return invokeUnpack(r, dest, options)
 }

pkg/chrootarchive/archive_unix.go

@@ -10,7 +10,6 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
-	"path/filepath"
 	"runtime"
 
 	"github.com/docker/docker/pkg/archive"
@@ -31,21 +30,11 @@ func untar() {
 		fatal(err)
 	}
 
-	dst := flag.Arg(0)
-	var root string
-	if len(flag.Args()) > 1 {
-		root = flag.Arg(1)
-	}
-
-	if root == "" {
-		root = dst
-	}
-
-	if err := chroot(root); err != nil {
+	if err := chroot(flag.Arg(0)); err != nil {
 		fatal(err)
 	}
 
-	if err := archive.Unpack(os.Stdin, dst, options); err != nil {
+	if err := archive.Unpack(os.Stdin, "/", options); err != nil {
 		fatal(err)
 	}
 	// fully consume stdin in case it is zero padded
@@ -56,7 +45,7 @@ func untar() {
 	os.Exit(0)
 }
 
-func invokeUnpack(decompressedArchive io.Reader, dest string, options *archive.TarOptions, root string) error {
+func invokeUnpack(decompressedArchive io.Reader, dest string, options *archive.TarOptions) error {
 
 	// We can't pass a potentially large exclude list directly via cmd line
 	// because we easily overrun the kernel's max argument/environment size
@@ -68,21 +57,7 @@ func invokeUnpack(decompressedArchive io.Reader, dest string, options *archive.T
 		return fmt.Errorf("Untar pipe failure: %v", err)
 	}
 
-	if root != "" {
-		relDest, err := filepath.Rel(root, dest)
-		if err != nil {
-			return err
-		}
-		if relDest == "." {
-			relDest = "/"
-		}
-		if relDest[0] != '/' {
-			relDest = "/" + relDest
-		}
-		dest = relDest
-	}
-
-	cmd := reexec.Command("docker-untar", dest, root)
+	cmd := reexec.Command("docker-untar", dest)
 	cmd.Stdin = decompressedArchive
 
 	cmd.ExtraFiles = append(cmd.ExtraFiles, r)
@@ -94,7 +69,6 @@ func invokeUnpack(decompressedArchive io.Reader, dest string, options *archive.T
 		w.Close()
 		return fmt.Errorf("Untar error on re-exec cmd: %v", err)
 	}
-
 	//write the options to the pipe for the untar exec to read
 	if err := json.NewEncoder(w).Encode(options); err != nil {
 		w.Close()

pkg/chrootarchive/archive_unix_test.go

@@ -1,77 +0,0 @@
-// +build !windows
-
-package chrootarchive
-
-import (
-	"bytes"
-	"io"
-	"io/ioutil"
-	"os"
-	"path/filepath"
-	"testing"
-
-	"github.com/docker/docker/pkg/archive"
-	"golang.org/x/sys/unix"
-	"gotest.tools/assert"
-)
-
-// Test for CVE-2018-15664
-// Assures that in the case where an "attacker" controlled path is a symlink to
-// some path outside of a container's rootfs that we do not copy data to a
-// container path that will actually overwrite data on the host
-func TestUntarWithMaliciousSymlinks(t *testing.T) {
-	dir, err := ioutil.TempDir("", t.Name())
-	assert.NilError(t, err)
-	defer os.RemoveAll(dir)
-
-	root := filepath.Join(dir, "root")
-
-	err = os.MkdirAll(root, 0755)
-	assert.NilError(t, err)
-
-	// Add a file into a directory above root
-	// Ensure that we can't access this file while tarring.
-	err = ioutil.WriteFile(filepath.Join(dir, "host-file"), []byte("I am a host file"), 0644)
-	assert.NilError(t, err)
-
-	// Create some data which which will be copied into the "container" root into
-	// the symlinked path.
-	// Before this change, the copy would overwrite the "host" content.
-	// With this change it should not.
-	data := filepath.Join(dir, "data")
-	err = os.MkdirAll(data, 0755)
-	assert.NilError(t, err)
-	err = ioutil.WriteFile(filepath.Join(data, "local-file"), []byte("pwn3d"), 0644)
-	assert.NilError(t, err)
-
-	safe := filepath.Join(root, "safe")
-	err = unix.Symlink(dir, safe)
-	assert.NilError(t, err)
-
-	rdr, err := archive.TarWithOptions(data, &archive.TarOptions{IncludeFiles: []string{"local-file"}, RebaseNames: map[string]string{"local-file": "host-file"}})
-	assert.NilError(t, err)
-
-	// Use tee to test both the good case and the bad case w/o recreating the archive
-	bufRdr := bytes.NewBuffer(nil)
-	tee := io.TeeReader(rdr, bufRdr)
-
-	err = UntarWithRoot(tee, safe, nil, root)
-	assert.Assert(t, err != nil)
-	assert.ErrorContains(t, err, "open /safe/host-file: no such file or directory")
-
-	// Make sure the "host" file is still in tact
-	// Before the fix the host file would be overwritten
-	hostData, err := ioutil.ReadFile(filepath.Join(dir, "host-file"))
-	assert.NilError(t, err)
-	assert.Equal(t, string(hostData), "I am a host file")
-
-	// Now test by chrooting to an attacker controlled path
-	// This should succeed as is and overwrite a "host" file
-	// Note that this would be a mis-use of this function.
-	err = UntarWithRoot(bufRdr, safe, nil, safe)
-	assert.NilError(t, err)
-
-	hostData, err = ioutil.ReadFile(filepath.Join(dir, "host-file"))
-	assert.NilError(t, err)
-	assert.Equal(t, string(hostData), "pwn3d")
-}

pkg/chrootarchive/archive_windows.go

@@ -14,7 +14,7 @@ func chroot(path string) error {
 
 func invokeUnpack(decompressedArchive io.ReadCloser,
 	dest string,
-	options *archive.TarOptions, root string) error {
+	options *archive.TarOptions) error {
 	// Windows is different to Linux here because Windows does not support
 	// chroot. Hence there is no point sandboxing a chrooted process to
 	// do the unpack. We call inline instead within the daemon process.