95 lines
2.8 KiB
Go
95 lines
2.8 KiB
Go
// +build linux
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package utils
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/*
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* Copyright 2016, 2017 SUSE LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import (
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"fmt"
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"os"
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"golang.org/x/sys/unix"
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)
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// MaxSendfdLen is the maximum length of the name of a file descriptor being
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// sent using SendFd. The name of the file handle returned by RecvFd will never
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// be larger than this value.
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const MaxNameLen = 4096
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// oobSpace is the size of the oob slice required to store a single FD. Note
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// that unix.UnixRights appears to make the assumption that fd is always int32,
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// so sizeof(fd) = 4.
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var oobSpace = unix.CmsgSpace(4)
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// RecvFd waits for a file descriptor to be sent over the given AF_UNIX
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// socket. The file name of the remote file descriptor will be recreated
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// locally (it is sent as non-auxiliary data in the same payload).
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func RecvFd(socket *os.File) (*os.File, error) {
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// For some reason, unix.Recvmsg uses the length rather than the capacity
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// when passing the msg_controllen and other attributes to recvmsg. So we
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// have to actually set the length.
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name := make([]byte, MaxNameLen)
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oob := make([]byte, oobSpace)
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sockfd := socket.Fd()
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n, oobn, _, _, err := unix.Recvmsg(int(sockfd), name, oob, 0)
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if err != nil {
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return nil, err
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}
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if n >= MaxNameLen || oobn != oobSpace {
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return nil, fmt.Errorf("recvfd: incorrect number of bytes read (n=%d oobn=%d)", n, oobn)
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}
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// Truncate.
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name = name[:n]
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oob = oob[:oobn]
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scms, err := unix.ParseSocketControlMessage(oob)
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if err != nil {
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return nil, err
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}
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if len(scms) != 1 {
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return nil, fmt.Errorf("recvfd: number of SCMs is not 1: %d", len(scms))
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}
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scm := scms[0]
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fds, err := unix.ParseUnixRights(&scm)
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if err != nil {
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return nil, err
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}
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if len(fds) != 1 {
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return nil, fmt.Errorf("recvfd: number of fds is not 1: %d", len(fds))
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}
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fd := uintptr(fds[0])
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return os.NewFile(fd, string(name)), nil
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}
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// SendFd sends a file descriptor over the given AF_UNIX socket. In
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// addition, the file.Name() of the given file will also be sent as
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// non-auxiliary data in the same payload (allowing to send contextual
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// information for a file descriptor).
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func SendFd(socket, file *os.File) error {
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name := []byte(file.Name())
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if len(name) >= MaxNameLen {
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return fmt.Errorf("sendfd: filename too long: %s", file.Name())
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}
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oob := unix.UnixRights(int(file.Fd()))
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return unix.Sendmsg(int(socket.Fd()), name, oob, nil, 0)
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}
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