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
131
132
|
/*
* privileges.go - Handles raising and dropping user privileges.
*
* Copyright 2017 Google Inc.
* Author: Joe Richey (joerichey@google.com)
*
* 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 security manages:
// - Keyring Operations (keyring.go)
// - Privilege manipulation (privileges.go)
// - Maintaining the link between the root and user keyrings.
package security
import (
"log"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
"github.com/google/fscrypt/util"
)
// Package security error values
var (
ErrReadingKeyList = util.SystemError("could not read keys from " + keyListFilename)
ErrFindingKeyring = util.SystemError("could not find user keyring")
ErrKeyringInsert = util.SystemError("could not insert key into the keyring")
ErrKeyringSearch = errors.New("could not find key with descriptor")
ErrKeyringDelete = util.SystemError("could not delete key from the keyring")
ErrKeyringLink = util.SystemError("could not link keyring")
ErrKeyringUnlink = util.SystemError("could not unlink keyring")
)
// Privileges contains the state needed to restore a user's original privileges.
type Privileges struct {
euid int
egid int
groups []int
}
// DropThreadPrivileges temporarily drops the privileges of the current thread
// to have the euid and egid specified. The returned opaque Privileges structure
// should later be passed to RestoreThreadPrivileges.
// Due to golang/go#1435, these privileges are only dropped for a single thread.
// This function also makes sure that the appropriate user keyrings are linked.
// This ensures that the user's keys are visible from commands like sudo.
func DropThreadPrivileges(euid int, egid int) (privs *Privileges, err error) {
privs = &Privileges{
euid: unix.Geteuid(),
egid: unix.Getegid(),
}
if privs.groups, err = unix.Getgroups(); err != nil {
return nil, errors.Wrapf(err, "getting groups")
}
// We link the privileged keyring into the thread keyring so that we
// can still modify it after dropping privileges.
privilegedUserKeyringID, err := getUserKeyringID()
if err != nil {
return
}
if err = keyringLink(privilegedUserKeyringID, unix.KEY_SPEC_THREAD_KEYRING); err != nil {
return
}
defer keyringUnlink(privilegedUserKeyringID, unix.KEY_SPEC_THREAD_KEYRING)
// Drop euid last so we have permissions to drop the others.
if err = unix.Setregid(-1, egid); err != nil {
err = errors.Wrapf(err, "dropping egid to %d", egid)
return
}
if err = unix.Setgroups([]int{egid}); err != nil {
err = errors.Wrapf(err, "dropping groups")
return
}
if err = unix.Setreuid(-1, euid); err != nil {
err = errors.Wrapf(err, "dropping euid to %d", euid)
return
}
log.Printf("privileges dropped to euid=%d, egid=%d", euid, egid)
// Failure should undo the privilege modification
defer func() {
if err != nil {
raiseErr := RaiseThreadPrivileges(privs)
log.Printf("when reverting privilege changes: %v", raiseErr)
}
}()
// If the link already exists, this linking does nothing and succeeds.
droppedUserKeyringID, err := getUserKeyringID()
if err != nil {
return
}
if err = keyringLink(droppedUserKeyringID, privilegedUserKeyringID); err != nil {
return
}
log.Printf("user keyring (%d) linked into root user keyring (%d)",
droppedUserKeyringID, privilegedUserKeyringID)
return privs, nil
}
// RaiseThreadPrivileges returns the state of a threads privileges to what it
// was before the call to DropThreadPrivileges.
func RaiseThreadPrivileges(privs *Privileges) error {
// Raise euid last so we have permissions to raise the others.
if err := unix.Setreuid(-1, privs.euid); err != nil {
return errors.Wrapf(err, "raising euid to %d", privs.euid)
}
if err := unix.Setregid(-1, privs.egid); err != nil {
return errors.Wrapf(err, "raising egid to %d", privs.egid)
}
if err := unix.Setgroups(privs.groups); err != nil {
return errors.Wrapf(err, "raising groups")
}
log.Printf("privileges raised to euid=%d, egid=%d", privs.euid, privs.egid)
return nil
}
|
