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/*
* util.go - Various helpers used throughout fscrypt
*
* 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 util contains useful components for simplifying Go code.
//
// The package contains common error types (errors.go) and functions for
// converting arrays to pointers.
package util
import (
"bufio"
"fmt"
"log"
"os"
"os/user"
"strconv"
"unsafe"
"golang.org/x/sys/unix"
)
// Ptr converts a Go byte array to a pointer to the start of the array.
func Ptr(slice []byte) unsafe.Pointer {
if len(slice) == 0 {
return nil
}
return unsafe.Pointer(&slice[0])
}
// ByteSlice takes a pointer to some data and views it as a slice of bytes.
// Note, indexing into this slice is unsafe.
func ByteSlice(ptr unsafe.Pointer) []byte {
// Slice must fit in the smallest address space go supports.
return (*[1 << 30]byte)(ptr)[:]
}
// PointerSlice takes a pointer to an array of pointers and views it as a slice
// of pointers. Note, indexing into this slice is unsafe.
func PointerSlice(ptr unsafe.Pointer) []unsafe.Pointer {
// Slice must fit in the smallest address space go supports.
return (*[1 << 28]unsafe.Pointer)(ptr)[:]
}
// Index returns the first index i such that inVal == inArray[i].
// ok is true if we find a match, false otherwise.
func Index(inVal int64, inArray []int64) (index int, ok bool) {
for index, val := range inArray {
if val == inVal {
return index, true
}
}
return 0, false
}
// Lookup finds inVal in inArray and returns the corresponding element in
// outArray. Specifically, if inVal == inArray[i], outVal == outArray[i].
// ok is true if we find a match, false otherwise.
func Lookup(inVal int64, inArray, outArray []int64) (outVal int64, ok bool) {
index, ok := Index(inVal, inArray)
if !ok {
return 0, false
}
return outArray[index], true
}
// MinInt returns the lesser of a and b.
func MinInt(a, b int) int {
if a < b {
return a
}
return b
}
// MaxInt returns the greater of a and b.
func MaxInt(a, b int) int {
if a > b {
return a
}
return b
}
// MinInt64 returns the lesser of a and b.
func MinInt64(a, b int64) int64 {
if a < b {
return a
}
return b
}
// ReadLine returns a line of input from standard input. An empty string is
// returned if the user didn't insert anything or on error.
func ReadLine() (string, error) {
scanner := bufio.NewScanner(os.Stdin)
scanner.Scan()
return scanner.Text(), scanner.Err()
}
// AtoiOrPanic converts a string to an int or it panics. Should only be used in
// situations where the input MUST be a decimal number.
func AtoiOrPanic(input string) int {
i, err := strconv.Atoi(input)
if err != nil {
panic(err)
}
return i
}
// UserFromUID returns the User corresponding to the given user id.
func UserFromUID(uid int64) (*user.User, error) {
return user.LookupId(strconv.FormatInt(uid, 10))
}
// EffectiveUser returns the user entry corresponding to the effective user.
func EffectiveUser() (*user.User, error) {
return UserFromUID(int64(os.Geteuid()))
}
// IsUserRoot checks if the effective user is root.
func IsUserRoot() bool {
return os.Geteuid() == 0
}
// Chown changes the owner of a File to a User.
func Chown(file *os.File, user *user.User) error {
uid := AtoiOrPanic(user.Uid)
gid := AtoiOrPanic(user.Gid)
return file.Chown(uid, gid)
}
// IsKernelVersionAtLeast returns true if the Linux kernel version is at least
// major.minor. If something goes wrong it assumes false.
func IsKernelVersionAtLeast(major, minor int) bool {
var uname unix.Utsname
if err := unix.Uname(&uname); err != nil {
log.Printf("Uname failed [%v], assuming old kernel", err)
return false
}
release := string(uname.Release[:])
log.Printf("Kernel version is %s", release)
var actualMajor, actualMinor int
if n, _ := fmt.Sscanf(release, "%d.%d", &actualMajor, &actualMinor); n != 2 {
log.Printf("Unrecognized uname format %q, assuming old kernel", release)
return false
}
return actualMajor > major ||
(actualMajor == major && actualMinor >= minor)
}
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