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samuelkarpdmcgowan
samuelkarp
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dmcgowan
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v1 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. Port of the same change for the v2 runtime Signed-off-by: Samuel Karp <[email protected]> (cherry picked from commit 6886c6a)
1 parent 97db45e commit 68119b4

2 files changed

Lines changed: 200 additions & 1 deletion

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‎runtime/v1/linux/bundle.go‎

Lines changed: 55 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@ package linux
2121
import (
2222
"context"
2323
"crypto/sha256"
24+
"encoding/json"
2425
"fmt"
2526
"io/ioutil"
2627
"os"
@@ -30,6 +31,7 @@ import (
3031
"github.com/containerd/containerd/runtime/linux/runctypes"
3132
"github.com/containerd/containerd/runtime/v1/shim"
3233
"github.com/containerd/containerd/runtime/v1/shim/client"
34+
"github.com/opencontainers/runtime-spec/specs-go"
3335
"github.com/pkg/errors"
3436
)
3537

@@ -48,14 +50,17 @@ func newBundle(id, path, workDir string, spec []byte) (b *bundle, err error) {
4850
return nil, err
4951
}
5052
path = filepath.Join(path, id)
51-
if err := os.Mkdir(path, 0711); err != nil {
53+
if err := os.Mkdir(path, 0700); err != nil {
5254
return nil, err
5355
}
5456
defer func() {
5557
if err != nil {
5658
os.RemoveAll(path)
5759
}
5860
}()
61+
if err := prepareBundleDirectoryPermissions(path, spec); err != nil {
62+
return nil, err
63+
}
5964
workDir = filepath.Join(workDir, id)
6065
if err := os.MkdirAll(workDir, 0711); err != nil {
6166
return nil, err
@@ -77,6 +82,55 @@ func newBundle(id, path, workDir string, spec []byte) (b *bundle, err error) {
7782
}, err
7883
}
7984

85+
// prepareBundleDirectoryPermissions prepares the permissions of the bundle
86+
// directory. When user namespaces are enabled, the permissions are modified
87+
// to allow the remapped root GID to access the bundle.
88+
func prepareBundleDirectoryPermissions(path string, spec []byte) error {
89+
gid, err := remappedGID(spec)
90+
if err != nil {
91+
return err
92+
}
93+
if gid == 0 {
94+
return nil
95+
}
96+
if err := os.Chown(path, -1, int(gid)); err != nil {
97+
return err
98+
}
99+
return os.Chmod(path, 0710)
100+
}
101+
102+
// ociSpecUserNS is a subset of specs.Spec used to reduce garbage during
103+
// unmarshal.
104+
type ociSpecUserNS struct {
105+
Linux *linuxSpecUserNS
106+
}
107+
108+
// linuxSpecUserNS is a subset of specs.Linux used to reduce garbage during
109+
// unmarshal.
110+
type linuxSpecUserNS struct {
111+
GIDMappings []specs.LinuxIDMapping
112+
}
113+
114+
// remappedGID reads the remapped GID 0 from the OCI spec, if it exists. If
115+
// there is no remapping, remappedGID returns 0. If the spec cannot be parsed,
116+
// remappedGID returns an error.
117+
func remappedGID(spec []byte) (uint32, error) {
118+
var ociSpec ociSpecUserNS
119+
err := json.Unmarshal(spec, &ociSpec)
120+
if err != nil {
121+
return 0, err
122+
}
123+
if ociSpec.Linux == nil || len(ociSpec.Linux.GIDMappings) == 0 {
124+
return 0, nil
125+
}
126+
for _, mapping := range ociSpec.Linux.GIDMappings {
127+
if mapping.ContainerID == 0 {
128+
return mapping.HostID, nil
129+
}
130+
}
131+
return 0, nil
132+
}
133+
80134
type bundle struct {
81135
id string
82136
path string

‎runtime/v1/linux/bundle_test.go‎

Lines changed: 145 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,145 @@
1+
//go:build linux
2+
// +build linux
3+
4+
/*
5+
Copyright The containerd Authors.
6+
7+
Licensed under the Apache License, Version 2.0 (the "License");
8+
you may not use this file except in compliance with the License.
9+
You may obtain a copy of the License at
10+
11+
http://www.apache.org/licenses/LICENSE-2.0
12+
13+
Unless required by applicable law or agreed to in writing, software
14+
distributed under the License is distributed on an "AS IS" BASIS,
15+
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16+
See the License for the specific language governing permissions and
17+
limitations under the License.
18+
*/
19+
20+
package linux
21+
22+
import (
23+
"encoding/json"
24+
"fmt"
25+
"io/ioutil"
26+
"os"
27+
"path/filepath"
28+
"strconv"
29+
"syscall"
30+
"testing"
31+
32+
"github.com/containerd/containerd/oci"
33+
"github.com/containerd/continuity/testutil"
34+
"github.com/opencontainers/runtime-spec/specs-go"
35+
"github.com/stretchr/testify/assert"
36+
"github.com/stretchr/testify/require"
37+
)
38+
39+
func TestNewBundle(t *testing.T) {
40+
testutil.RequiresRoot(t)
41+
tests := []struct {
42+
userns bool
43+
}{{
44+
userns: false,
45+
}, {
46+
userns: true,
47+
}}
48+
const usernsGID = 4200
49+
50+
for i, tc := range tests {
51+
t.Run(strconv.Itoa(i), func(t *testing.T) {
52+
dir, err := ioutil.TempDir("", "test-new-bundle")
53+
require.NoError(t, err, "failed to create test directory")
54+
defer os.RemoveAll(dir)
55+
work := filepath.Join(dir, "work")
56+
state := filepath.Join(dir, "state")
57+
id := fmt.Sprintf("new-bundle-%d", i)
58+
spec := oci.Spec{}
59+
if tc.userns {
60+
spec.Linux = &specs.Linux{
61+
GIDMappings: []specs.LinuxIDMapping{{ContainerID: 0, HostID: usernsGID}},
62+
}
63+
}
64+
specBytes, err := json.Marshal(&spec)
65+
require.NoError(t, err, "failed to marshal spec")
66+
67+
b, err := newBundle(id, work, state, specBytes)
68+
require.NoError(t, err, "newBundle should succeed")
69+
require.NotNil(t, b, "bundle should not be nil")
70+
71+
fi, err := os.Stat(b.path)
72+
assert.NoError(t, err, "should be able to stat bundle path")
73+
if tc.userns {
74+
assert.Equal(t, os.ModeDir|0710, fi.Mode(), "bundle path should be a directory with perm 0710")
75+
} else {
76+
assert.Equal(t, os.ModeDir|0700, fi.Mode(), "bundle path should be a directory with perm 0700")
77+
}
78+
stat, ok := fi.Sys().(*syscall.Stat_t)
79+
require.True(t, ok, "should assert to *syscall.Stat_t")
80+
expectedGID := uint32(0)
81+
if tc.userns {
82+
expectedGID = usernsGID
83+
}
84+
assert.Equal(t, expectedGID, stat.Gid, "gid should match")
85+
86+
})
87+
}
88+
}
89+
90+
func TestRemappedGID(t *testing.T) {
91+
tests := []struct {
92+
spec oci.Spec
93+
gid uint32
94+
}{{
95+
// empty spec
96+
spec: oci.Spec{},
97+
gid: 0,
98+
}, {
99+
// empty Linux section
100+
spec: oci.Spec{
101+
Linux: &specs.Linux{},
102+
},
103+
gid: 0,
104+
}, {
105+
// empty ID mappings
106+
spec: oci.Spec{
107+
Linux: &specs.Linux{
108+
GIDMappings: make([]specs.LinuxIDMapping, 0),
109+
},
110+
},
111+
gid: 0,
112+
}, {
113+
// valid ID mapping
114+
spec: oci.Spec{
115+
Linux: &specs.Linux{
116+
GIDMappings: []specs.LinuxIDMapping{{
117+
ContainerID: 0,
118+
HostID: 1000,
119+
}},
120+
},
121+
},
122+
gid: 1000,
123+
}, {
124+
// missing ID mapping
125+
spec: oci.Spec{
126+
Linux: &specs.Linux{
127+
GIDMappings: []specs.LinuxIDMapping{{
128+
ContainerID: 100,
129+
HostID: 1000,
130+
}},
131+
},
132+
},
133+
gid: 0,
134+
}}
135+
136+
for i, tc := range tests {
137+
t.Run(strconv.Itoa(i), func(t *testing.T) {
138+
s, err := json.Marshal(tc.spec)
139+
require.NoError(t, err, "failed to marshal spec")
140+
gid, err := remappedGID(s)
141+
assert.NoError(t, err, "should unmarshal successfully")
142+
assert.Equal(t, tc.gid, gid, "expected GID to match")
143+
})
144+
}
145+
}

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