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// Copyright 2018 Google Inc.
//
// 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"
"sync"
"gvisor.googlesource.com/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: Consider supporting disabling setgroups(2), which "was
// added in Linux 3.19, but was backported to many earlier stable kernel
// series, because it addresses a security issue" - user_namespaces(7). (It
// was not backported to 3.11.10, which we are currently imitating.)
}
// 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, syserror.EPERM
}
if !c.EffectiveKGID.In(c.UserNamespace).Ok() {
return nil, syserror.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
}
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