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/*
* login.go - Checks the validity of a login token key against PAM.
*
* 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 pam contains all the functionality for interfacing with Linux
// Pluggable Authentication Modules (PAM). Currently, all this package does is
// check the validity of a user's login passphrase.
// See http://www.linux-pam.org/Linux-PAM-html/ for more information.
package pam
import "C"
import (
"fmt"
"log"
"sync"
"github.com/pkg/errors"
"github.com/google/fscrypt/crypto"
"github.com/google/fscrypt/util"
)
// Pam error values
var (
ErrPassphrase = errors.New("incorrect login passphrase")
)
// Global state is needed for the PAM callback, so we guard this function with a
// lock. tokenToCheck is only ever non-nil when tokenLock is held.
var (
tokenLock sync.Mutex
tokenToCheck *crypto.Key
)
// userInput is run when the callback needs some input from the user. We prompt
// the user for information and return their answer. A return value of nil
// indicates an error occurred.
//
//export userInput
func userInput(prompt *C.char) *C.char {
fmt.Print(C.GoString(prompt))
input, err := util.ReadLine()
if err != nil {
log.Printf("getting input for PAM: %s", err)
return nil
}
return C.CString(input)
}
// passphraseInput is run when the callback needs a passphrase from the user. We
// pass along the tokenToCheck without prompting. A return value of nil
// indicates an error occurred.
//
//export passphraseInput
func passphraseInput(prompt *C.char) *C.char {
log.Printf("getting secret data for PAM: %q", C.GoString(prompt))
if tokenToCheck == nil {
log.Print("secret data requested multiple times")
return nil
}
// Subsequent calls to passphrase input should fail
input := (*C.char)(tokenToCheck.UnsafeToCString())
tokenToCheck = nil
return input
}
// IsUserLoginToken returns nil if the presented token is the user's login key,
// and returns an error otherwise. Note that unless we are currently running as
// root, this check will only work for the user running this process.
func IsUserLoginToken(username string, token *crypto.Key, quiet bool) error {
log.Printf("Checking login token for %s", username)
// We require global state for the function. This function never takes
// ownership of the token, so it is not responsible for wiping it.
tokenLock.Lock()
tokenToCheck = token
defer func() {
tokenToCheck = nil
tokenLock.Unlock()
}()
transaction, err := Start("fscrypt", username)
if err != nil {
return err
}
defer transaction.End()
// Ask PAM to authenticate the token.
authenticated, err := transaction.Authenticate(quiet)
if err != nil {
return err
}
if !authenticated {
return ErrPassphrase
}
return nil
}
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