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path: root/Godeps/_workspace/src/github.com/microsoft/go-winio/privilege.go
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package winio

import (
    "bytes"
    "encoding/binary"
    "fmt"
    "runtime"
    "syscall"
    "unicode/utf16"
)

//sys adjustTokenPrivileges(token syscall.Handle, releaseAll bool, input *byte, outputSize uint32, output *byte, requiredSize *uint32) (success bool, err error) [true] = advapi32.AdjustTokenPrivileges
//sys impersonateSelf(level uint32) (err error) = advapi32.ImpersonateSelf
//sys revertToSelf() (err error) = advapi32.RevertToSelf
//sys openThreadToken(thread syscall.Handle, accessMask uint32, openAsSelf bool, token *syscall.Handle) (err error) = advapi32.OpenThreadToken
//sys getCurrentThread() (h syscall.Handle) = GetCurrentThread
//sys lookupPrivilegeValue(systemName string, name string, luid *uint64) (err error) = advapi32.LookupPrivilegeValueW
//sys lookupPrivilegeName(systemName string, luid *uint64, buffer *uint16, size *uint32) (err error) = advapi32.LookupPrivilegeNameW
//sys lookupPrivilegeDisplayName(systemName string, name *uint16, buffer *uint16, size *uint32, languageId *uint32) (err error) = advapi32.LookupPrivilegeDisplayNameW

const (
    SE_PRIVILEGE_ENABLED = 2

    ERROR_NOT_ALL_ASSIGNED syscall.Errno = 1300

    SeBackupPrivilege  = "SeBackupPrivilege"
    SeRestorePrivilege = "SeRestorePrivilege"
)

const (
    securityAnonymous = iota
    securityIdentification
    securityImpersonation
    securityDelegation
)

type PrivilegeError struct {
    privileges []uint64
}

func (e *PrivilegeError) Error() string {
    s := ""
    if len(e.privileges) > 1 {
        s = "Could not enable privileges "
    } else {
        s = "Could not enable privilege "
    }
    for i, p := range e.privileges {
        if i != 0 {
            s += ", "
        }
        s += `"`
        s += getPrivilegeName(p)
        s += `"`
    }
    return s
}

func RunWithPrivilege(name string, fn func() error) error {
    return RunWithPrivileges([]string{name}, fn)
}

func RunWithPrivileges(names []string, fn func() error) error {
    var privileges []uint64
    for _, name := range names {
        p := uint64(0)
        err := lookupPrivilegeValue("", name, &p)
        if err != nil {
            return err
        }
        privileges = append(privileges, p)
    }
    runtime.LockOSThread()
    defer runtime.UnlockOSThread()
    token, err := newThreadToken()
    if err != nil {
        return err
    }
    defer releaseThreadToken(token)
    err = adjustPrivileges(token, privileges)
    if err != nil {
        return err
    }
    return fn()
}

func adjustPrivileges(token syscall.Handle, privileges []uint64) error {
    var b bytes.Buffer
    binary.Write(&b, binary.LittleEndian, uint32(len(privileges)))
    for _, p := range privileges {
        binary.Write(&b, binary.LittleEndian, p)
        binary.Write(&b, binary.LittleEndian, uint32(SE_PRIVILEGE_ENABLED))
    }
    prevState := make([]byte, b.Len())
    reqSize := uint32(0)
    success, err := adjustTokenPrivileges(token, false, &b.Bytes()[0], uint32(len(prevState)), &prevState[0], &reqSize)
    if !success {
        return err
    }
    if err == ERROR_NOT_ALL_ASSIGNED {
        return &PrivilegeError{privileges}
    }
    return nil
}

func getPrivilegeName(luid uint64) string {
    var nameBuffer [256]uint16
    bufSize := uint32(len(nameBuffer))
    err := lookupPrivilegeName("", &luid, &nameBuffer[0], &bufSize)
    if err != nil {
        return fmt.Sprintf("<unknown privilege %d>", luid)
    }

    var displayNameBuffer [256]uint16
    displayBufSize := uint32(len(displayNameBuffer))
    var langId uint32
    err = lookupPrivilegeDisplayName("", &nameBuffer[0], &displayNameBuffer[0], &displayBufSize, &langId)
    if err != nil {
        return fmt.Sprintf("<unknown privilege %s>", utf16.Decode(nameBuffer[:bufSize]))
    }

    return string(utf16.Decode(displayNameBuffer[:displayBufSize]))
}

func newThreadToken() (syscall.Handle, error) {
    err := impersonateSelf(securityImpersonation)
    if err != nil {
        panic(err)
        return 0, err
    }

    var token syscall.Handle
    err = openThreadToken(getCurrentThread(), syscall.TOKEN_ADJUST_PRIVILEGES|syscall.TOKEN_QUERY, false, &token)
    if err != nil {
        rerr := revertToSelf()
        if rerr != nil {
            panic(rerr)
        }
        return 0, err
    }
    return token, nil
}

func releaseThreadToken(h syscall.Handle) {
    err := revertToSelf()
    if err != nil {
        panic(err)
    }
    syscall.Close(h)
}