From 7d56b24f1a9af82dfaa10ff55a4e3c36a7efd943 Mon Sep 17 00:00:00 2001 From: Samuel Karp Date: Mon, 20 Sep 2021 16:20:26 -0700 Subject: [PATCH] v2 runtime: reduce permissions for bundle dir Bundle directory permissions should be 0700 by default. On Linux with user namespaces enabled, the remapped root also needs access to the bundle directory. In this case, the bundle directory is modified to 0710 and group ownership is changed to the remapped root group. Signed-off-by: Samuel Karp --- runtime/v2/bundle.go | 5 +- runtime/v2/bundle_default.go | 24 ++++++ runtime/v2/bundle_linux.go | 74 ++++++++++++++++ runtime/v2/bundle_linux_test.go | 145 ++++++++++++++++++++++++++++++++ runtime/v2/bundle_test.go | 23 +++++ 5 files changed, 270 insertions(+), 1 deletion(-) create mode 100644 runtime/v2/bundle_default.go create mode 100644 runtime/v2/bundle_linux.go create mode 100644 runtime/v2/bundle_linux_test.go create mode 100644 runtime/v2/bundle_test.go diff --git a/runtime/v2/bundle.go b/runtime/v2/bundle.go index 1a58e627b..954163b0f 100644 --- a/runtime/v2/bundle.go +++ b/runtime/v2/bundle.go @@ -72,7 +72,10 @@ func NewBundle(ctx context.Context, root, state, id string, spec []byte) (b *Bun if err := os.MkdirAll(filepath.Dir(b.Path), 0711); err != nil { return nil, err } - if err := os.Mkdir(b.Path, 0711); err != nil { + if err := os.Mkdir(b.Path, 0700); err != nil { + return nil, err + } + if err := prepareBundleDirectoryPermissions(b.Path, spec); err != nil { return nil, err } paths = append(paths, b.Path) diff --git a/runtime/v2/bundle_default.go b/runtime/v2/bundle_default.go new file mode 100644 index 000000000..2be40c825 --- /dev/null +++ b/runtime/v2/bundle_default.go @@ -0,0 +1,24 @@ +//go:build !linux +// +build !linux + +/* + Copyright The containerd Authors. + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +*/ + +package v2 + +// prepareBundleDirectoryPermissions prepares the permissions of the bundle +// directory according to the needs of the current platform. +func prepareBundleDirectoryPermissions(path string, spec []byte) error { return nil } diff --git a/runtime/v2/bundle_linux.go b/runtime/v2/bundle_linux.go new file mode 100644 index 000000000..5f1915d77 --- /dev/null +++ b/runtime/v2/bundle_linux.go @@ -0,0 +1,74 @@ +/* + Copyright The containerd Authors. + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +*/ + +package v2 + +import ( + "encoding/json" + "os" + + "github.com/opencontainers/runtime-spec/specs-go" +) + +// prepareBundleDirectoryPermissions prepares the permissions of the bundle +// directory according to the needs of the current platform. +// On Linux when user namespaces are enabled, the permissions are modified to +// allow the remapped root GID to access the bundle. +func prepareBundleDirectoryPermissions(path string, spec []byte) error { + gid, err := remappedGID(spec) + if err != nil { + return err + } + if gid == 0 { + return nil + } + if err := os.Chown(path, -1, int(gid)); err != nil { + return err + } + return os.Chmod(path, 0710) +} + +// ociSpecUserNS is a subset of specs.Spec used to reduce garbage during +// unmarshal. +type ociSpecUserNS struct { + Linux *linuxSpecUserNS +} + +// linuxSpecUserNS is a subset of specs.Linux used to reduce garbage during +// unmarshal. +type linuxSpecUserNS struct { + GIDMappings []specs.LinuxIDMapping +} + +// remappedGID reads the remapped GID 0 from the OCI spec, if it exists. If +// there is no remapping, remappedGID returns 0. If the spec cannot be parsed, +// remappedGID returns an error. +func remappedGID(spec []byte) (uint32, error) { + var ociSpec ociSpecUserNS + err := json.Unmarshal(spec, &ociSpec) + if err != nil { + return 0, err + } + if ociSpec.Linux == nil || len(ociSpec.Linux.GIDMappings) == 0 { + return 0, nil + } + for _, mapping := range ociSpec.Linux.GIDMappings { + if mapping.ContainerID == 0 { + return mapping.HostID, nil + } + } + return 0, nil +} diff --git a/runtime/v2/bundle_linux_test.go b/runtime/v2/bundle_linux_test.go new file mode 100644 index 000000000..1828fb8cf --- /dev/null +++ b/runtime/v2/bundle_linux_test.go @@ -0,0 +1,145 @@ +/* + Copyright The containerd Authors. + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +*/ + +package v2 + +import ( + "context" + "encoding/json" + "fmt" + "io/ioutil" + "os" + "path/filepath" + "strconv" + "syscall" + "testing" + + "github.com/containerd/containerd/namespaces" + "github.com/containerd/containerd/oci" + "github.com/containerd/containerd/pkg/testutil" + "github.com/opencontainers/runtime-spec/specs-go" + "github.com/stretchr/testify/assert" + "github.com/stretchr/testify/require" +) + +func TestNewBundle(t *testing.T) { + testutil.RequiresRoot(t) + tests := []struct { + userns bool + }{{ + userns: false, + }, { + userns: true, + }} + const usernsGID = 4200 + + for i, tc := range tests { + t.Run(strconv.Itoa(i), func(t *testing.T) { + dir, err := ioutil.TempDir("", "test-new-bundle") + require.NoError(t, err, "failed to create test directory") + defer os.RemoveAll(dir) + work := filepath.Join(dir, "work") + state := filepath.Join(dir, "state") + id := fmt.Sprintf("new-bundle-%d", i) + spec := oci.Spec{} + if tc.userns { + spec.Linux = &specs.Linux{ + GIDMappings: []specs.LinuxIDMapping{{ContainerID: 0, HostID: usernsGID}}, + } + } + specBytes, err := json.Marshal(&spec) + require.NoError(t, err, "failed to marshal spec") + + ctx := namespaces.WithNamespace(context.TODO(), namespaces.Default) + b, err := NewBundle(ctx, work, state, id, specBytes) + require.NoError(t, err, "NewBundle should succeed") + require.NotNil(t, b, "bundle should not be nil") + + fi, err := os.Stat(b.Path) + assert.NoError(t, err, "should be able to stat bundle path") + if tc.userns { + assert.Equal(t, os.ModeDir|0710, fi.Mode(), "bundle path should be a directory with perm 0710") + } else { + assert.Equal(t, os.ModeDir|0700, fi.Mode(), "bundle path should be a directory with perm 0700") + } + stat, ok := fi.Sys().(*syscall.Stat_t) + require.True(t, ok, "should assert to *syscall.Stat_t") + expectedGID := uint32(0) + if tc.userns { + expectedGID = usernsGID + } + assert.Equal(t, expectedGID, stat.Gid, "gid should match") + + }) + } +} + +func TestRemappedGID(t *testing.T) { + tests := []struct { + spec oci.Spec + gid uint32 + }{{ + // empty spec + spec: oci.Spec{}, + gid: 0, + }, { + // empty Linux section + spec: oci.Spec{ + Linux: &specs.Linux{}, + }, + gid: 0, + }, { + // empty ID mappings + spec: oci.Spec{ + Linux: &specs.Linux{ + GIDMappings: make([]specs.LinuxIDMapping, 0), + }, + }, + gid: 0, + }, { + // valid ID mapping + spec: oci.Spec{ + Linux: &specs.Linux{ + GIDMappings: []specs.LinuxIDMapping{{ + ContainerID: 0, + HostID: 1000, + }}, + }, + }, + gid: 1000, + }, { + // missing ID mapping + spec: oci.Spec{ + Linux: &specs.Linux{ + GIDMappings: []specs.LinuxIDMapping{{ + ContainerID: 100, + HostID: 1000, + }}, + }, + }, + gid: 0, + }} + + for i, tc := range tests { + t.Run(strconv.Itoa(i), func(t *testing.T) { + s, err := json.Marshal(tc.spec) + require.NoError(t, err, "failed to marshal spec") + gid, err := remappedGID(s) + assert.NoError(t, err, "should unmarshal successfully") + assert.Equal(t, tc.gid, gid, "expected GID to match") + }) + } +} diff --git a/runtime/v2/bundle_test.go b/runtime/v2/bundle_test.go new file mode 100644 index 000000000..54e5f24cc --- /dev/null +++ b/runtime/v2/bundle_test.go @@ -0,0 +1,23 @@ +/* + Copyright The containerd Authors. + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +*/ + +package v2 + +import ( + // When testutil is imported for one platform (bundle_linux_test.go) it + // should be imported for all platforms. + _ "github.com/containerd/containerd/pkg/testutil" +)