1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
// Copyright 2018 The gVisor 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 auth
import (
"math"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
)
// A UserNamespace represents a user namespace. See user_namespaces(7) for
// details.
//
// +stateify savable
type UserNamespace struct {
// parent is this namespace's parent. If this is the root namespace, parent
// is nil. The parent pointer is immutable.
parent *UserNamespace
// owner is the effective UID of the namespace's creator in the root
// namespace. owner is immutable.
owner KUID
// mu protects the following fields.
//
// If mu will be locked in multiple UserNamespaces, it must be locked in
// descendant namespaces before ancestors.
mu sync.Mutex `state:"nosave"`
// Mappings of user/group IDs between this namespace and its parent.
//
// All ID maps, once set, cannot be changed. This means that successful
// UID/GID translations cannot be racy.
uidMapFromParent idMapSet
uidMapToParent idMapSet
gidMapFromParent idMapSet
gidMapToParent idMapSet
// TODO(b/27454212): Support disabling setgroups(2).
}
// NewRootUserNamespace returns a UserNamespace that is appropriate for a
// system's root user namespace.
func NewRootUserNamespace() *UserNamespace {
var ns UserNamespace
// """
// The initial user namespace has no parent namespace, but, for
// consistency, the kernel provides dummy user and group ID mapping files
// for this namespace. Looking at the uid_map file (gid_map is the same)
// from a shell in the initial namespace shows:
//
// $ cat /proc/$$/uid_map
// 0 0 4294967295
// """ - user_namespaces(7)
for _, m := range []*idMapSet{
&ns.uidMapFromParent,
&ns.uidMapToParent,
&ns.gidMapFromParent,
&ns.gidMapToParent,
} {
if !m.Add(idMapRange{0, math.MaxUint32}, 0) {
panic("Failed to insert into empty ID map")
}
}
return &ns
}
// Root returns the root of the user namespace tree containing ns.
func (ns *UserNamespace) Root() *UserNamespace {
for ns.parent != nil {
ns = ns.parent
}
return ns
}
// "The kernel imposes (since version 3.11) a limit of 32 nested levels of user
// namespaces." - user_namespaces(7)
const maxUserNamespaceDepth = 32
func (ns *UserNamespace) depth() int {
var i int
for ns != nil {
i++
ns = ns.parent
}
return i
}
// NewChildUserNamespace returns a new user namespace created by a caller with
// credentials c.
func (c *Credentials) NewChildUserNamespace() (*UserNamespace, error) {
if c.UserNamespace.depth() >= maxUserNamespaceDepth {
// "... Calls to unshare(2) or clone(2) that would cause this limit to
// be exceeded fail with the error EUSERS." - user_namespaces(7)
return nil, syserror.EUSERS
}
// "EPERM: CLONE_NEWUSER was specified in flags, but either the effective
// user ID or the effective group ID of the caller does not have a mapping
// in the parent namespace (see user_namespaces(7))." - clone(2)
// "CLONE_NEWUSER requires that the user ID and group ID of the calling
// process are mapped to user IDs and group IDs in the user namespace of
// the calling process at the time of the call." - unshare(2)
if !c.EffectiveKUID.In(c.UserNamespace).Ok() {
return nil, linuxerr.EPERM
}
if !c.EffectiveKGID.In(c.UserNamespace).Ok() {
return nil, linuxerr.EPERM
}
return &UserNamespace{
parent: c.UserNamespace,
owner: c.EffectiveKUID,
// "When a user namespace is created, it starts without a mapping of
// user IDs (group IDs) to the parent user namespace." -
// user_namespaces(7)
}, nil
}
|
