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Revert "Pass root to chroot to for chroot Untar" 

This reverts commit 9781cceb09.

Signed-off-by: Tibor Vass <tibor@docker.com>
This commit is contained in:
Tibor Vass 2019-06-12 04:06:21 +00:00
parent 96df6d4d0b
commit 60013ba69b
5 changed files with 12 additions and 132 deletions
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7
daemon/archive.go
View File

@ -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
}

24
pkg/chrootarchive/archive.go
View File

@ -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)
}

34
pkg/chrootarchive/archive_unix.go
View File

@ -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()

77
pkg/chrootarchive/archive_unix_test.go
View File

@ -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")
}

2
pkg/chrootarchive/archive_windows.go
View File

@ -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.