Fix handling of Linux network namespaces

The CNI plugins upstream removed their network namespace creation
code, making it a test package only. Copy it into our repository
and slightly modify it for our use (most notably, use MNT_DETACH
when unmounting namespaces).

This new CNI code splits closing and unmounting network
namespaces, which allows us to greatly reduce the number of
occasions on which we call teardownNetwork() and make more errors
in that function fatal instead of warnings. Instead, we can call
Close() and just close the open file descriptor in cases where
the namespace has already been cleaned up.

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>

Closes: #1165
Approved by: baude

1 files changed, 161 insertions, 0 deletions

diff --git a/pkg/netns/netns_linux.go b/pkg/netns/netns_linux.go
new file mode 100644
index 000000000..f88939f11
--- /dev/null
+++ b/pkg/netns/netns_linux.go
@@ -0,0 +1,161 @@
+// 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"
+
+// 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())
+}