Merge pull request #6026 from vmarmol/nsenter
Adding initial version of C-based nsenter for allowing execin in libcontainer.
This commit is contained in:
Victor Vieux
commit
7e96f8de1c
3 changed files with 229 additions and 102 deletions
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@ -3,119 +3,54 @@
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package namespaces
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import (
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"fmt"
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"encoding/json"
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"os"
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"path/filepath"
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"strconv"
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"syscall"
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"github.com/dotcloud/docker/pkg/label"
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"github.com/dotcloud/docker/pkg/libcontainer"
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"github.com/dotcloud/docker/pkg/libcontainer/mount"
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"github.com/dotcloud/docker/pkg/system"
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)
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// ExecIn uses an existing pid and joins the pid's namespaces with the new command.
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func ExecIn(container *libcontainer.Container, nspid int, args []string) (int, error) {
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// clear the current processes env and replace it with the environment
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// defined on the container
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if err := LoadContainerEnvironment(container); err != nil {
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return -1, err
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func ExecIn(container *libcontainer.Container, nspid int, args []string) error {
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// TODO(vmarmol): If this gets too long, send it over a pipe to the child.
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// Marshall the container into JSON since it won't be available in the namespace.
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containerJson, err := json.Marshal(container)
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if err != nil {
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return err
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}
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for key, enabled := range container.Namespaces {
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// skip the PID namespace on unshare because it it not supported
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if enabled && key != "NEWPID" {
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if ns := libcontainer.GetNamespace(key); ns != nil {
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if err := system.Unshare(ns.Value); err != nil {
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return -1, err
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}
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}
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}
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}
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fds, err := getNsFds(nspid, container)
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closeFds := func() {
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for _, f := range fds {
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system.Closefd(f)
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}
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}
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if err != nil {
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closeFds()
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return -1, err
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}
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// TODO(vmarmol): Move this to the container JSON.
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processLabel, err := label.GetPidCon(nspid)
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if err != nil {
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closeFds()
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return -1, err
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}
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// foreach namespace fd, use setns to join an existing container's namespaces
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for _, fd := range fds {
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if fd > 0 {
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if err := system.Setns(fd, 0); err != nil {
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closeFds()
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return -1, fmt.Errorf("setns %s", err)
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}
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}
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system.Closefd(fd)
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return err
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}
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// if the container has a new pid and mount namespace we need to
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// remount proc and sys to pick up the changes
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if container.Namespaces["NEWNS"] && container.Namespaces["NEWPID"] {
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pid, err := system.Fork()
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if err != nil {
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return -1, err
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}
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if pid == 0 {
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// TODO: make all raw syscalls to be fork safe
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if err := system.Unshare(syscall.CLONE_NEWNS); err != nil {
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return -1, err
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}
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if err := mount.RemountProc(); err != nil {
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return -1, fmt.Errorf("remount proc %s", err)
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}
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if err := mount.RemountSys(); err != nil {
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return -1, fmt.Errorf("remount sys %s", err)
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}
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goto dropAndExec
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}
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proc, err := os.FindProcess(pid)
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if err != nil {
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return -1, err
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}
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state, err := proc.Wait()
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if err != nil {
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return -1, err
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}
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os.Exit(state.Sys().(syscall.WaitStatus).ExitStatus())
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}
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dropAndExec:
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if err := FinalizeNamespace(container); err != nil {
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return -1, err
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}
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err = label.SetProcessLabel(processLabel)
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if err != nil {
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return -1, err
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}
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if err := system.Execv(args[0], args[0:], container.Env); err != nil {
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return -1, err
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// Enter the namespace and then finish setup
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finalArgs := []string{os.Args[0], "nsenter", strconv.Itoa(nspid), processLabel, string(containerJson)}
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finalArgs = append(finalArgs, args...)
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if err := system.Execv(finalArgs[0], finalArgs[0:], os.Environ()); err != nil {
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return err
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}
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panic("unreachable")
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}
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func getNsFds(pid int, container *libcontainer.Container) ([]uintptr, error) {
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fds := []uintptr{}
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for key, enabled := range container.Namespaces {
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if enabled {
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if ns := libcontainer.GetNamespace(key); ns != nil {
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f, err := os.OpenFile(filepath.Join("/proc/", strconv.Itoa(pid), "ns", ns.File), os.O_RDONLY, 0)
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if err != nil {
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return fds, err
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}
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fds = append(fds, f.Fd())
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}
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}
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// NsEnter is run after entering the namespace.
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func NsEnter(container *libcontainer.Container, processLabel string, nspid int, args []string) error {
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// clear the current processes env and replace it with the environment
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// defined on the container
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if err := LoadContainerEnvironment(container); err != nil {
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return err
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}
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return fds, nil
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if err := FinalizeNamespace(container); err != nil {
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return err
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}
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if err := label.SetProcessLabel(processLabel); err != nil {
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return err
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}
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if err := system.Execv(args[0], args[0:], container.Env); err != nil {
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return err
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}
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panic("unreachable")
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}
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143
pkg/libcontainer/namespaces/nsenter.go
Normal file
143
pkg/libcontainer/namespaces/nsenter.go
Normal file
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@ -0,0 +1,143 @@
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package namespaces
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/*
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#include <dirent.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/sched.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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static const kBufSize = 256;
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void get_args(int *argc, char ***argv) {
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// Read argv
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int fd = open("/proc/self/cmdline", O_RDONLY);
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// Read the whole commandline.
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ssize_t contents_size = 0;
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ssize_t contents_offset = 0;
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char *contents = NULL;
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ssize_t bytes_read = 0;
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do {
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contents_size += kBufSize;
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contents = (char *) realloc(contents, contents_size);
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bytes_read = read(fd, contents + contents_offset, contents_size - contents_offset);
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contents_offset += bytes_read;
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} while (bytes_read > 0);
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close(fd);
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// Parse the commandline into an argv. /proc/self/cmdline has \0 delimited args.
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ssize_t i;
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*argc = 0;
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for (i = 0; i < contents_offset; i++) {
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if (contents[i] == '\0') {
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(*argc)++;
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}
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}
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*argv = (char **) malloc(sizeof(char *) * ((*argc) + 1));
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int idx;
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for (idx = 0; idx < (*argc); idx++) {
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(*argv)[idx] = contents;
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contents += strlen(contents) + 1;
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}
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(*argv)[*argc] = NULL;
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}
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void nsenter() {
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int argc;
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char **argv;
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get_args(&argc, &argv);
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// Ignore if this is not for us.
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if (argc < 2 || strcmp(argv[1], "nsenter") != 0) {
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return;
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}
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// USAGE: <binary> nsenter <PID> <process label> <container JSON> <argv>...
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if (argc < 6) {
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fprintf(stderr, "nsenter: Incorrect usage, not enough arguments\n");
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exit(1);
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}
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pid_t init_pid = strtol(argv[2], NULL, 10);
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if (errno != 0 || init_pid <= 0) {
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fprintf(stderr, "nsenter: Failed to parse PID from \"%s\" with error: \"%s\"\n", argv[2], strerror(errno));
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exit(1);
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}
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argc -= 3;
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argv += 3;
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// Setns on all supported namespaces.
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char ns_dir[kBufSize];
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memset(ns_dir, 0, kBufSize);
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if (snprintf(ns_dir, kBufSize - 1, "/proc/%d/ns/", init_pid) < 0) {
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fprintf(stderr, "nsenter: Error getting ns dir path with error: \"%s\"\n", strerror(errno));
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exit(1);
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}
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struct dirent *dent;
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DIR *dir = opendir(ns_dir);
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if (dir == NULL) {
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fprintf(stderr, "nsenter: Failed to open directory \"%s\" with error: \"%s\"\n", ns_dir, strerror(errno));
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exit(1);
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}
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while((dent = readdir(dir)) != NULL) {
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if(strcmp(dent->d_name, ".") == 0 || strcmp(dent->d_name, "..") == 0 || strcmp(dent->d_name, "user") == 0) {
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continue;
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}
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// Get and open the namespace for the init we are joining..
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char buf[kBufSize];
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memset(buf, 0, kBufSize);
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strncat(buf, ns_dir, kBufSize - 1);
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strncat(buf, dent->d_name, kBufSize - 1);
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int fd = open(buf, O_RDONLY);
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if (fd == -1) {
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fprintf(stderr, "nsenter: Failed to open ns file \"%s\" for ns \"%s\" with error: \"%s\"\n", buf, dent->d_name, strerror(errno));
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exit(1);
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}
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// Set the namespace.
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if (setns(fd, 0) == -1) {
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fprintf(stderr, "nsenter: Failed to setns for \"%s\" with error: \"%s\"\n", dent->d_name, strerror(errno));
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exit(1);
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}
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close(fd);
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}
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closedir(dir);
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// We must fork to actually enter the PID namespace.
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int child = fork();
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if (child == 0) {
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// Finish executing, let the Go runtime take over.
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return;
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} else {
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// Parent, wait for the child.
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int status = 0;
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if (waitpid(child, &status, 0) == -1) {
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fprintf(stderr, "nsenter: Failed to waitpid with error: \"%s\"\n", strerror(errno));
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exit(1);
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}
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// Forward the child's exit code or re-send its death signal.
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if (WIFEXITED(status)) {
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exit(WEXITSTATUS(status));
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} else if (WIFSIGNALED(status)) {
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kill(getpid(), WTERMSIG(status));
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}
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exit(1);
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}
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return;
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}
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__attribute__((constructor)) init() {
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nsenter();
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}
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*/
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import "C"
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@ -27,20 +27,20 @@ func main() {
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log.Fatalf("invalid number of arguments %d", len(os.Args))
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}
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container, err := loadContainer()
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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switch os.Args[1] {
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case "exec": // this is executed outside of the namespace in the cwd
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container, err := loadContainer()
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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var nspid, exitCode int
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if nspid, err = readPid(); err != nil && !os.IsNotExist(err) {
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log.Fatalf("unable to read pid: %s", err)
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}
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if nspid > 0 {
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exitCode, err = namespaces.ExecIn(container, nspid, os.Args[2:])
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err = namespaces.ExecIn(container, nspid, os.Args[2:])
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} else {
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term := namespaces.NewTerminal(os.Stdin, os.Stdout, os.Stderr, container.Tty)
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exitCode, err = startContainer(container, term, dataPath, os.Args[2:])
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@ -50,7 +50,36 @@ func main() {
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log.Fatalf("failed to exec: %s", err)
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}
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os.Exit(exitCode)
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case "nsenter": // this is executed inside the namespace.
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// nsinit nsenter <pid> <process label> <container JSON> <cmd>...
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if len(os.Args) < 6 {
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log.Fatalf("incorrect usage: nsinit nsenter <pid> <process label> <container JSON> <cmd>...")
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}
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container, err := loadContainerFromJson(os.Args[4])
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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nspid, err := strconv.Atoi(os.Args[2])
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if err != nil {
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log.Fatalf("unable to read pid: %s from %q", err, os.Args[2])
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}
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if nspid <= 0 {
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log.Fatalf("cannot enter into namespaces without valid pid: %q", nspid)
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}
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err = namespaces.NsEnter(container, os.Args[3], nspid, os.Args[5:])
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if err != nil {
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log.Fatalf("failed to nsenter: %s", err)
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}
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case "init": // this is executed inside of the namespace to setup the container
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container, err := loadContainer()
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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// by default our current dir is always our rootfs
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rootfs, err := os.Getwd()
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if err != nil {
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@ -70,6 +99,11 @@ func main() {
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log.Fatalf("unable to initialize for container: %s", err)
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}
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case "stats":
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container, err := loadContainer()
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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// returns the stats of the current container.
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stats, err := getContainerStats(container)
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if err != nil {
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@ -80,6 +114,11 @@ func main() {
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os.Exit(0)
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case "spec":
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container, err := loadContainer()
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if err != nil {
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log.Fatalf("unable to load container: %s", err)
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}
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// returns the spec of the current container.
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spec, err := getContainerSpec(container)
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if err != nil {
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@ -90,13 +129,14 @@ func main() {
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os.Exit(0)
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default:
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log.Fatalf("command not supported for nsinit %s", os.Args[0])
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log.Fatalf("command not supported for nsinit %s", os.Args[1])
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}
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}
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func loadContainer() (*libcontainer.Container, error) {
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f, err := os.Open(filepath.Join(dataPath, "container.json"))
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if err != nil {
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log.Printf("Path: %q", filepath.Join(dataPath, "container.json"))
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return nil, err
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}
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defer f.Close()
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@ -108,6 +148,15 @@ func loadContainer() (*libcontainer.Container, error) {
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return container, nil
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}
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func loadContainerFromJson(rawData string) (*libcontainer.Container, error) {
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container := &libcontainer.Container{}
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err := json.Unmarshal([]byte(rawData), container)
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if err != nil {
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return nil, err
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}
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return container, nil
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}
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func readPid() (int, error) {
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data, err := ioutil.ReadFile(filepath.Join(dataPath, "pid"))
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if err != nil {
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