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// Copyright 2018 CNI authors
//
// 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.
// This file was originally a part of the containernetworking/plugins
// repository.
// It was copied here and modified for local use by the libpod maintainers.
package netns
import (
"crypto/rand"
"fmt"
"os"
"path"
"runtime"
"strings"
"sync"
"github.com/containernetworking/plugins/pkg/ns"
"golang.org/x/sys/unix"
)
const nsRunDir = "/var/run/netns"
// NewNS creates a new persistent (bind-mounted) network namespace and returns
// an object representing that namespace, without switching to it.
func NewNS() (ns.NetNS, error) {
b := make([]byte, 16)
_, err := rand.Reader.Read(b)
if err != nil {
return nil, fmt.Errorf("failed to generate random netns name: %v", err)
}
// Create the directory for mounting network namespaces
// This needs to be a shared mountpoint in case it is mounted in to
// other namespaces (containers)
err = os.MkdirAll(nsRunDir, 0755)
if err != nil {
return nil, err
}
// Remount the namespace directory shared. This will fail if it is not
// already a mountpoint, so bind-mount it on to itself to "upgrade" it
// to a mountpoint.
err = unix.Mount("", nsRunDir, "none", unix.MS_SHARED|unix.MS_REC, "")
if err != nil {
if err != unix.EINVAL {
return nil, fmt.Errorf("mount --make-rshared %s failed: %q", nsRunDir, err)
}
// Recursively remount /var/run/netns on itself. The recursive flag is
// so that any existing netns bindmounts are carried over.
err = unix.Mount(nsRunDir, nsRunDir, "none", unix.MS_BIND|unix.MS_REC, "")
if err != nil {
return nil, fmt.Errorf("mount --rbind %s %s failed: %q", nsRunDir, nsRunDir, err)
}
// Now we can make it shared
err = unix.Mount("", nsRunDir, "none", unix.MS_SHARED|unix.MS_REC, "")
if err != nil {
return nil, fmt.Errorf("mount --make-rshared %s failed: %q", nsRunDir, err)
}
}
nsName := fmt.Sprintf("cni-%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:])
// create an empty file at the mount point
nsPath := path.Join(nsRunDir, nsName)
mountPointFd, err := os.Create(nsPath)
if err != nil {
return nil, err
}
mountPointFd.Close()
// Ensure the mount point is cleaned up on errors; if the namespace
// was successfully mounted this will have no effect because the file
// is in-use
defer os.RemoveAll(nsPath)
var wg sync.WaitGroup
wg.Add(1)
// do namespace work in a dedicated goroutine, so that we can safely
// Lock/Unlock OSThread without upsetting the lock/unlock state of
// the caller of this function
go (func() {
defer wg.Done()
runtime.LockOSThread()
// Don't unlock. By not unlocking, golang will kill the OS thread when the
// goroutine is done (for go1.10+)
var origNS ns.NetNS
origNS, err = ns.GetNS(getCurrentThreadNetNSPath())
if err != nil {
return
}
defer origNS.Close()
// create a new netns on the current thread
err = unix.Unshare(unix.CLONE_NEWNET)
if err != nil {
return
}
// Put this thread back to the orig ns, since it might get reused (pre go1.10)
defer origNS.Set()
// bind mount the netns from the current thread (from /proc) onto the
// mount point. This causes the namespace to persist, even when there
// are no threads in the ns.
err = unix.Mount(getCurrentThreadNetNSPath(), nsPath, "none", unix.MS_BIND, "")
if err != nil {
err = fmt.Errorf("failed to bind mount ns at %s: %v", nsPath, err)
}
})()
wg.Wait()
if err != nil {
return nil, fmt.Errorf("failed to create namespace: %v", err)
}
return ns.GetNS(nsPath)
}
// UnmountNS unmounts the NS held by the netns object
func UnmountNS(ns ns.NetNS) error {
nsPath := ns.Path()
// Only unmount if it's been bind-mounted (don't touch namespaces in /proc...)
if strings.HasPrefix(nsPath, nsRunDir) {
if err := unix.Unmount(nsPath, unix.MNT_DETACH); err != nil {
return fmt.Errorf("failed to unmount NS: at %s: %v", nsPath, err)
}
if err := os.Remove(nsPath); err != nil {
return fmt.Errorf("failed to remove ns path %s: %v", nsPath, err)
}
}
return nil
}
// getCurrentThreadNetNSPath copied from pkg/ns
func getCurrentThreadNetNSPath() string {
// /proc/self/ns/net returns the namespace of the main thread, not
// of whatever thread this goroutine is running on. Make sure we
// use the thread's net namespace since the thread is switching around
return fmt.Sprintf("/proc/%d/task/%d/ns/net", os.Getpid(), unix.Gettid())
}
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