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// +build !windows
package chrootarchive
import (
gotar "archive/tar"
"bytes"
"io"
"io/ioutil"
"os"
"path"
"path/filepath"
"strings"
"testing"
"github.com/docker/docker/pkg/archive"
"golang.org/x/sys/unix"
"gotest.tools/v3/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")
}
// 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 unwittingly leak
// host data into the archive.
func TestTarWithMaliciousSymlinks(t *testing.T) {
dir, err := ioutil.TempDir("", t.Name())
assert.NilError(t, err)
// defer os.RemoveAll(dir)
t.Log(dir)
root := filepath.Join(dir, "root")
err = os.MkdirAll(root, 0755)
assert.NilError(t, err)
hostFileData := []byte("I am a host file")
// 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"), hostFileData, 0644)
assert.NilError(t, err)
safe := filepath.Join(root, "safe")
err = unix.Symlink(dir, safe)
assert.NilError(t, err)
data := filepath.Join(dir, "data")
err = os.MkdirAll(data, 0755)
assert.NilError(t, err)
type testCase struct {
p string
includes []string
}
cases := []testCase{
{p: safe, includes: []string{"host-file"}},
{p: safe + "/", includes: []string{"host-file"}},
{p: safe, includes: nil},
{p: safe + "/", includes: nil},
{p: root, includes: []string{"safe/host-file"}},
{p: root, includes: []string{"/safe/host-file"}},
{p: root, includes: nil},
}
maxBytes := len(hostFileData)
for _, tc := range cases {
t.Run(path.Join(tc.p+"_"+strings.Join(tc.includes, "_")), func(t *testing.T) {
// Here if we use archive.TarWithOptions directly or change the "root" parameter
// to be the same as "safe", data from the host will be leaked into the archive
var opts *archive.TarOptions
if tc.includes != nil {
opts = &archive.TarOptions{
IncludeFiles: tc.includes,
}
}
rdr, err := Tar(tc.p, opts, root)
assert.NilError(t, err)
defer rdr.Close()
tr := gotar.NewReader(rdr)
assert.Assert(t, !isDataInTar(t, tr, hostFileData, int64(maxBytes)), "host data leaked to archive")
})
}
}
func isDataInTar(t *testing.T, tr *gotar.Reader, compare []byte, maxBytes int64) bool {
for {
h, err := tr.Next()
if err == io.EOF {
break
}
assert.NilError(t, err)
if h.Size == 0 {
continue
}
assert.Assert(t, h.Size <= maxBytes, "%s: file size exceeds max expected size %d: %d", h.Name, maxBytes, h.Size)
data := make([]byte, int(h.Size))
_, err = io.ReadFull(tr, data)
assert.NilError(t, err)
if bytes.Contains(data, compare) {
return true
}
}
return false
}
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