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/*
* privileges.go - Handles inserting/removing into user keyrings.
*
* 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
import (
"bytes"
"fmt"
"io/ioutil"
"log"
"strconv"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
)
const (
// file which lists all visible keys
keyListFilename = "/proc/keys"
// keyType is always logon as required by filesystem encryption.
keyType = "logon"
)
// FindKey tries to locate a key in the kernel keyring with the provided
// description. The key id is returned if we can find the key. An error is
// returned if the key does not exist.
func FindKey(description string) (int, error) {
keyringID, err := getUserKeyringID()
if err != nil {
return 0, err
}
keyID, err := unix.KeyctlSearch(keyringID, keyType, description, 0)
log.Printf("KeyctlSearch(%d, %s, %s) = %d, %v", keyringID, keyType, description, keyID, err)
if err != nil {
return 0, errors.Wrap(ErrKeyringSearch, err.Error())
}
return keyID, err
}
// RemoveKey tries to remove a policy key from the kernel keyring with the
// provided description. An error is returned if the key does not exist.
func RemoveKey(description string) error {
keyID, err := FindKey(description)
if err != nil {
return err
}
// We use KEYCTL_INVALIDATE instead of KEYCTL_REVOKE because
// invalidating a key immediately removes it.
_, err = unix.KeyctlInt(unix.KEYCTL_INVALIDATE, keyID, 0, 0, 0)
log.Printf("KeyctlInvalidate(%d) = %v", keyID, err)
if err != nil {
return errors.Wrap(ErrKeyringDelete, err.Error())
}
return nil
}
// InsertKey puts the provided data into the kernel keyring with the provided
// description.
func InsertKey(data []byte, description string) error {
keyringID, err := getUserKeyringID()
if err != nil {
return err
}
keyID, err := unix.AddKey(keyType, description, data, keyringID)
log.Printf("KeyctlAddKey(%s, %s, <data>, %d) = %d, %v",
keyType, description, keyringID, keyID, err)
if err != nil {
return errors.Wrap(ErrKeyringInsert, err.Error())
}
return nil
}
var keyringIDCache = make(map[int]int)
// getUserKeyringID returns the key id of the current user's user keyring. A
// simpler approach would be to use
// unix.KeyctlGetKeyringID(unix.KEY_SPEC_USER_KEYRING, false)
// which would work in almost all cases. However, despite the fact that the rest
// of the keyrings API uses the _effective_ UID throughout, the translation of
// KEY_SPEC_USER_KEYRING is done with respect to the _real_ UID. This means that
// a simpler implementation would not respect permissions dropping.
func getUserKeyringID() (int, error) {
// We will cache the result of this function.
euid := unix.Geteuid()
if keyringID, ok := keyringIDCache[euid]; ok {
return keyringID, nil
}
data, err := ioutil.ReadFile(keyListFilename)
if err != nil {
log.Print(err)
return 0, ErrReadingKeyList
}
expectedName := fmt.Sprintf("_uid.%d:", euid)
for _, line := range bytes.Split(data, []byte{'\n'}) {
if len(line) == 0 {
continue
}
// Each line in /proc/keys should have 9 columns.
columns := bytes.Fields(line)
if len(columns) < 9 {
return 0, ErrReadingKeyList
}
hexID := string(columns[0])
owner := string(columns[5])
name := string(columns[8])
// Our desired key is owned by the user and has the right name.
// The owner check is so another user cannot DOS this user by
// inserting a keyring with a similar name.
if owner != strconv.Itoa(euid) || name != expectedName {
continue
}
// The keyring's ID is encoded as hex.
parsedID, err := strconv.ParseInt(hexID, 16, 32)
if err != nil {
log.Print(err)
return 0, ErrReadingKeyList
}
keyringID := int(parsedID)
// For some stupid reason, a thread does not automaticaly "possess" keys
// in the user keyring. So we link it into the process keyring so that
// we will not get "permission denied" when purging or modifying keys.
if err := keyringLink(keyringID, unix.KEY_SPEC_PROCESS_KEYRING); err != nil {
return 0, err
}
keyringIDCache[euid] = keyringID
return keyringID, nil
}
return 0, ErrFindingKeyring
}
func keyringLink(keyID int, keyringID int) error {
_, err := unix.KeyctlInt(unix.KEYCTL_LINK, keyID, keyringID, 0, 0)
log.Printf("KeyctlLink(%d, %d) = %v", keyID, keyringID, err)
if err != nil {
return errors.Wrap(ErrKeyringLink, err.Error())
}
return err
}
func keyringUnlink(keyID int, keyringID int) error {
_, err := unix.KeyctlInt(unix.KEYCTL_UNLINK, keyID, keyringID, 0, 0)
log.Printf("KeyctlUnlink(%d, %d) = %v", keyID, keyringID, err)
if err != nil {
return errors.Wrap(ErrKeyringUnlink, err.Error())
}
return err
}
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