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main: if unprivileged, reexec in a user namespace 

If our CLI is invoked as an unprivileged user (uid != 0),
* create a namespace using our own UID and GID as "0" followed by the
  ranges matching our name and our primary group's name that we find in
  /etc/subuid and /etc/subgid (the latter by way of using newuidmap and
  newgidmap)
* re-exec ourselves inside of that user namespace, prepending global CLI arguments that:
  * override the driver from storage.conf with "vfs"
  * override the storage root from storage.conf with a "containers/storage" subdirectory
    of $XDG_DATA_HOME, or $HOME/.local/share.
  * override the storage runroot from storage.conf with either "$XDG_RUNTIME_DIR/run" or
    "/var/run/user/$uid/run"
  * set default ID mapping settings to map all of the ranges matching
    our name and our primary group's name that we found in /etc/subuid
    and /etc/subgid
  * can still be overridden using the command line

Add a "buildah unshare" CLI that will start an arbitrary command in the
first namespace, so that manual cleanup of locations used by the second
namespace will be possible.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #823
Approved by: rhatdan
This commit is contained in:
Nalin Dahyabhai 2018-06-14 15:42:33 -04:00 committed by Atomic Bot
parent 1accccec61
commit 18063d19b6
15 changed files with 1019 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Makefile
View File

@ -17,7 +17,7 @@ LDFLAGS := -ldflags '-X main.gitCommit=${GIT_COMMIT} -X main.buildInfo=${BUILD_I
all: buildah imgtype docs
buildah: *.go imagebuildah/*.go bind/*.go cmd/buildah/*.go docker/*.go pkg/cli/*.go pkg/parse/*.go util/*.go
buildah: *.go imagebuildah/*.go bind/*.go cmd/buildah/*.go docker/*.go pkg/cli/*.go pkg/parse/*.go unshare/*.c unshare/*.go util/*.go
$(GO) build $(LDFLAGS) -o buildah $(BUILDFLAGS) ./cmd/buildah
imgtype: *.go docker/*.go util/*.go tests/imgtype/imgtype.go

2
cmd/buildah/main.go
View File

@ -81,6 +81,7 @@ func main() {
debug = true
logrus.SetLevel(logrus.DebugLevel)
}
maybeReexecUsingUserNamespace(c, false)
return nil
}
app.After = func(c *cli.Context) error {
@ -110,6 +111,7 @@ func main() {
runCommand,
tagCommand,
umountCommand,
unshareCommand,
versionCommand,
}
err := app.Run(os.Args)

234
cmd/buildah/unshare.go Normal file
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@ -0,0 +1,234 @@
// +build linux
package main
import (
"bytes"
"fmt"
"os"
"os/exec"
"os/user"
"runtime"
"strconv"
"syscall"
"github.com/opencontainers/runtime-spec/specs-go"
"github.com/pkg/errors"
"github.com/projectatomic/buildah/unshare"
"github.com/projectatomic/buildah/util"
"github.com/sirupsen/logrus"
"github.com/urfave/cli"
)
const (
// startedInUserNS is an environment variable that, if set, means that we shouldn't try
// to create and enter a new user namespace and then re-exec ourselves.
startedInUserNS = "_BUILDAH_STARTED_IN_USERNS"
)
var (
unshareDescription = "Runs a command in a modified user namespace"
unshareCommand = cli.Command{
Name: "unshare",
Usage: "Run a command in a modified user namespace",
Description: unshareDescription,
Action: unshareCmd,
ArgsUsage: "[COMMAND [ARGS [...]]]",
SkipArgReorder: true,
}
)
type runnable interface {
Run() error
}
func maybeReexecUsingUserNamespace(c *cli.Context, evenForRoot bool) {
// If we've already been through this once, no need to try again.
if os.Getenv(startedInUserNS) != "" {
return
}
// Figure out if we're already root, or "root", which is close enough,
// unless we've been explicitly told to do this even for root.
me, err := user.Current()
if err != nil {
logrus.Errorf("error determining current user: %v", err)
cli.OsExiter(1)
}
if me.Uid == "0" && !evenForRoot {
return
}
uidNum, err := strconv.ParseUint(me.Uid, 10, 32)
if err != nil {
logrus.Errorf("error parsing current UID %s: %v", me.Uid, err)
cli.OsExiter(1)
}
gidNum, err := strconv.ParseUint(me.Gid, 10, 32)
if err != nil {
logrus.Errorf("error parsing current GID %s: %v", me.Gid, err)
cli.OsExiter(1)
}
runtime.LockOSThread()
defer runtime.UnlockOSThread()
// Read the set of ID mappings that we're allowed to use. Each range
// in /etc/subuid and /etc/subgid file is a starting ID and a range size.
uidmap, gidmap, err := util.GetSubIDMappings(me.Username, me.Username)
if err != nil {
logrus.Errorf("error reading allowed ID mappings: %v", err)
cli.OsExiter(1)
}
if len(uidmap) == 0 {
logrus.Warnf("Found no UID ranges set aside for user %q in /etc/subuid.", me.Username)
}
if len(gidmap) == 0 {
logrus.Warnf("Found no GID ranges set aside for user %q in /etc/subgid.", me.Username)
}
// Build modified maps that map us to uid/gid 0, and maps every other
// range to itself. In a namespace that uses this map, the invoking
// user will appear to be root. This should let us create storage
// directories and access credentials under the invoking user's home
// directory.
uidmap2 := append([]specs.LinuxIDMapping{{HostID: uint32(uidNum), ContainerID: 0, Size: 1}}, uidmap...)
for i := range uidmap2[1:] {
uidmap2[i+1].ContainerID = uidmap2[i+1].HostID
}
gidmap2 := append([]specs.LinuxIDMapping{{HostID: uint32(gidNum), ContainerID: 0, Size: 1}}, gidmap...)
for i := range gidmap2[1:] {
gidmap2[i+1].ContainerID = gidmap2[i+1].HostID
}
// Map the uidmap and gidmap ranges, consecutively, starting at 0.
// When used to created a namespace inside of a namespace that uses the
// maps we've created above, they'll produce mappings which don't map
// in the invoking user. This is more suitable for running commands in
// containers, so we'll want to use it as a default for any containers
// that we create.
umap := new(bytes.Buffer)
for i := range uidmap {
if i > 0 {
fmt.Fprintf(umap, ",")
}
fmt.Fprintf(umap, "%d:%d:%d", uidmap[i].ContainerID, uidmap[i].HostID, uidmap[i].Size)
}
gmap := new(bytes.Buffer)
for i := range gidmap {
if i > 0 {
fmt.Fprintf(gmap, ",")
}
fmt.Fprintf(gmap, "%d:%d:%d", gidmap[i].ContainerID, gidmap[i].HostID, gidmap[i].Size)
}
// Add args to change the global defaults.
defaultStorageDriver := "vfs"
defaultRoot, err := util.UnsharedRootPath(me.HomeDir)
if err != nil {
logrus.Errorf("%v", err)
cli.OsExiter(1)
}
defaultRunroot, err := util.UnsharedRunrootPath(me.Uid)
if err != nil {
logrus.Errorf("%v", err)
cli.OsExiter(1)
}
var moreArgs []string
if !c.GlobalIsSet("storage-driver") || !c.GlobalIsSet("root") || !c.GlobalIsSet("runroot") || (!c.GlobalIsSet("userns-uid-map") && !c.GlobalIsSet("userns-gid-map")) {
logrus.Infof("Running without privileges, assuming arguments:")
if !c.GlobalIsSet("storage-driver") {
logrus.Infof(" --storage-driver %q", defaultStorageDriver)
moreArgs = append(moreArgs, "--storage-driver", defaultStorageDriver)
}
if !c.GlobalIsSet("root") {
logrus.Infof(" --root %q", defaultRoot)
moreArgs = append(moreArgs, "--root", defaultRoot)
}
if !c.GlobalIsSet("runroot") {
logrus.Infof(" --runroot %q", defaultRunroot)
moreArgs = append(moreArgs, "--runroot", defaultRunroot)
}
if !c.GlobalIsSet("userns-uid-map") && !c.GlobalIsSet("userns-gid-map") && umap.Len() > 0 && gmap.Len() > 0 {
logrus.Infof(" --userns-uid-map %q --userns-gid-map %q", umap.String(), gmap.String())
moreArgs = append(moreArgs, "--userns-uid-map", umap.String(), "--userns-gid-map", gmap.String())
}
}
// Unlike most uses of reexec or unshare, we're using a name that
// _won't_ be recognized as a registered reexec handler, since we
// _want_ to fall through reexec.Init() to the normal main().
cmd := unshare.Command(append(append([]string{"buildah-unprivileged"}, moreArgs...), os.Args[1:]...)...)
// If, somehow, we don't become UID 0 in our child, indicate that the child shouldn't try again.
if err = os.Setenv(startedInUserNS, "1"); err != nil {
logrus.Errorf("error setting %s=1 in environment: %v", startedInUserNS, err)
os.Exit(1)
}
// Reuse our stdio.
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
// Set up a new user namespace with the ID mapping.
cmd.UnshareFlags = syscall.CLONE_NEWUSER
cmd.UseNewuidmap = true
cmd.UidMappings = uidmap2
cmd.UseNewgidmap = true
cmd.GidMappings = gidmap2
cmd.GidMappingsEnableSetgroups = true
// Finish up.
logrus.Debugf("running %+v with environment %+v, UID map %+v, and GID map %+v", cmd.Cmd.Args, os.Environ(), cmd.UidMappings, cmd.GidMappings)
execRunnable(cmd)
}
// execRunnable runs the specified unshare command, captures its exit status,
// and exits with the same status.
func execRunnable(cmd runnable) {
if err := cmd.Run(); err != nil {
if exitError, ok := errors.Cause(err).(*exec.ExitError); ok {
if exitError.ProcessState.Exited() {
if waitStatus, ok := exitError.ProcessState.Sys().(syscall.WaitStatus); ok {
if waitStatus.Exited() {
logrus.Errorf("%v", exitError)
os.Exit(waitStatus.ExitStatus())
}
if waitStatus.Signaled() {
logrus.Errorf("%v", exitError)
os.Exit(int(waitStatus.Signal()) + 128)
}
}
}
}
logrus.Errorf("%v", err)
logrus.Errorf("(unable to determine exit status)")
os.Exit(1)
}
os.Exit(0)
}
// unshareCmd execs whatever using the ID mappings that we want to use for ourselves
func unshareCmd(c *cli.Context) error {
// force reexec using the configured ID mappings
maybeReexecUsingUserNamespace(c, true)
// exec the specified command, if there is one
args := c.Args()
if len(args) < 1 {
// try to exec the shell, if one's set
shell, shellSet := os.LookupEnv("SHELL")
if !shellSet {
logrus.Errorf("no command specified")
os.Exit(1)
}
args = []string{shell}
}
cmd := exec.Command(args[0], args[1:]...)
cmd.Env = append(os.Environ(), "USER=root", "USERNAME=root", "GROUP=root", "LOGNAME=root", "UID=0", "GID=0")
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
execRunnable(cmd)
os.Exit(1)
return nil
}

16
cmd/buildah/unshare_unsupported.go Normal file
View File

@ -0,0 +1,16 @@
// +build !linux
package main
var (
unshareCommand = cli.Command{
Name: "unshare",
Hidden: true,
Action: func(c *cli.Context) error { return nil },
SkipArgReorder: true,
}
)
func maybeReexecUsingUserNamespace(c *cli.Context, evenForRoot bool) {
return
}

13
contrib/completions/bash/buildah
View File

@ -753,6 +753,16 @@ return 1
esac
}
_buildah_unshare() {
local boolean_options="
--help
-h
"
local options_with_args="
"
}
_buildah_version() {
local boolean_options="
--help
@ -761,7 +771,7 @@ return 1
local options_with_args="
"
}
}
_buildah() {
local previous_extglob_setting=$(shopt -p extglob)
@ -787,6 +797,7 @@ return 1
tag
umount
unmount
unshare
version
)

3
contrib/rpm/buildah.spec
View File

@ -27,7 +27,7 @@
Name: buildah
# Bump version in buildah.go too
Version: 1.2
Release: 1.git%{shortcommit}%{?dist}
Release: 2.git%{shortcommit}%{?dist}
Summary: A command line tool used to creating OCI Images
License: ASL 2.0
URL: https://%{provider_prefix}
@ -49,6 +49,7 @@ BuildRequires: make
Requires: runc >= 1.0.0-6
Requires: container-selinux
Requires: skopeo-containers
Requires: shadow-utils
Provides: %{repo} = %{version}-%{release}
%description

32
docs/buildah-unshare.md Normal file
View File

@ -0,0 +1,32 @@
# buildah-unshare "19" "June 2018" "buildah"
## NAME
buildah\-unshare - Run a command inside of a modified user namespace.
## SYNOPSIS
**buildah** **unshare** [*options* [...] --] [**command**]
## DESCRIPTION
Launches a process (by default, *$SHELL*) in a new user namespace. The user
namespace is configured so that the invoking user's UID and primary GID appear
to be UID 0 and GID 0, respectively. Any ranges which match that user and
group in /etc/subuid and /etc/subgid are also mapped in as themselves with the
help of the *newuidmap(1)* and *newgidmap(1)* helpers.
This is mainly useful for troubleshooting unprivileged operations and for
manually clearing storage and other data related to images and containers.
## EXAMPLE
buildah unshare id
buildah unshare pwd
buildah unshare cat /proc/self/uid\_map
buildah unshare cat /proc/self/gid\_map
buildah unshare rm -fr $HOME/.local/share/containers/storage /var/run/user/\`id -u\`/run
## SEE ALSO
buildah(1), namespaces(7), newuidmap(1), newgidmap(1), user\_namespaces(7)

17
docs/buildah.md
View File

@ -46,23 +46,23 @@ be used, as the default behavior of using the system-wide configuration
**--root** **value**
Storage root dir (default: "/var/lib/containers/storage")
Storage root dir (default: "/var/lib/containers/storage" for UID 0, "$HOME/.local/share/containers/storage" for other users)
Default root dir is configured in /etc/containers/storage.conf
**--runroot** **value**
Storage state dir (default: "/var/run/containers/storage")
Storage state dir (default: "/var/run/containers/storage" for UID 0, "/var/run/user/$UID/run" for other users)
Default state dir is configured in /etc/containers/storage.conf
**--storage-driver** **value**
Storage driver. Default Storage driver is configured in /etc/containers/storage.conf. Overriding
this option, will drop the storage-opt definitions was well from the storage.conf file. User must
Storage driver. The default storage driver for UID 0 is configured in /etc/containers/storage.conf, and is *vfs* for other users.
Overriding this option will cause the *storage-opt* settings in /etc/containers/storage.conf to be ignored. The user must
specify additional options via the `--storage-opt` flag.
**--storage-opt** **value**
Storage driver option, Default Storage driver options are configured in /etc/containers/storage.conf
Storage driver option, Default storage driver options are configured in /etc/containers/storage.conf
**--userns-uid-map** *mapping*
@ -107,8 +107,9 @@ Print the version
| buildah-run(1) | Run a command inside of the container. |
| buildah-tag(1) | Add an additional name to a local image. |
| buildah-umount(1) | Unmount a working container's root file system. |
| buildah-version(1) | Display the Buildah Version Information |
| storage.conf(5) | Syntax of Container Storage configuration file |
| buildah-unshare(1) | Launch a command in a user namespace with modified ID mappings. |
| buildah-version(1) | Display the Buildah Version Information |
| storage.conf(5) | Syntax of Container Storage configuration file |
## Files
@ -134,7 +135,7 @@ Print the version
registries.conf is the configuration file which specifies which container registries should be consulted when completing image names which do not include a registry or domain portion.
## SEE ALSO
podman(1), mounts.conf(5), registries.conf(5), storage.conf(5)
podman(1), mounts.conf(5), newuidmap(1), newgidmap(1), registries.conf(5), storage.conf(5)
## HISTORY
December 2017, Originally compiled by Tom Sweeney <tsweeney@redhat.com>

110
unshare/unshare.c Normal file
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@ -0,0 +1,110 @@
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <grp.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
static int _buildah_unshare_parse_envint(const char *envname) {
char *p, *q;
long l;
p = getenv(envname);
if (p == NULL) {
return -1;
}
q = NULL;
l = strtol(p, &q, 10);
if ((q == NULL) || (*q != '\0')) {
fprintf(stderr, "Error parsing \"%s\"=\"%s\"!\n", envname, p);
_exit(1);
}
unsetenv(envname);
return l;
}
void _buildah_unshare(void)
{
int flags, pidfd, continuefd, n, pgrp, sid, ctty, allow_setgroups;
char buf[2048];
flags = _buildah_unshare_parse_envint("_Buildah-unshare");
if (flags == -1) {
return;
}
if ((flags & CLONE_NEWUSER) != 0) {
if (unshare(CLONE_NEWUSER) == -1) {
fprintf(stderr, "Error during unshare(CLONE_NEWUSER): %m\n");
_exit(1);
}
}
pidfd = _buildah_unshare_parse_envint("_Buildah-pid-pipe");
if (pidfd != -1) {
snprintf(buf, sizeof(buf), "%llu", (unsigned long long) getpid());
if (write(pidfd, buf, strlen(buf)) != strlen(buf)) {
fprintf(stderr, "Error writing PID to pipe on fd %d: %m\n", pidfd);
_exit(1);
}
close(pidfd);
}
continuefd = _buildah_unshare_parse_envint("_Buildah-continue-pipe");
if (continuefd != -1) {
n = read(continuefd, buf, sizeof(buf));
if (n > 0) {
fprintf(stderr, "Error: %.*s\n", n, buf);
_exit(1);
}
close(continuefd);
}
sid = _buildah_unshare_parse_envint("_Buildah-setsid");
if (sid == 1) {
if (setsid() == -1) {
fprintf(stderr, "Error during setsid: %m\n");
_exit(1);
}
}
pgrp = _buildah_unshare_parse_envint("_Buildah-setpgrp");
if (pgrp == 1) {
if (setpgrp() == -1) {
fprintf(stderr, "Error during setpgrp: %m\n");
_exit(1);
}
}
ctty = _buildah_unshare_parse_envint("_Buildah-ctty");
if (ctty != -1) {
if (ioctl(ctty, TIOCSCTTY, 0) == -1) {
fprintf(stderr, "Error while setting controlling terminal to %d: %m\n", ctty);
_exit(1);
}
}
allow_setgroups = _buildah_unshare_parse_envint("_Buildah-allow-setgroups");
if ((flags & CLONE_NEWUSER) != 0) {
if (allow_setgroups == 1) {
if (setgroups(0, NULL) != 0) {
fprintf(stderr, "Error during setgroups(0, NULL): %m\n");
_exit(1);
}
}
if (setresgid(0, 0, 0) != 0) {
fprintf(stderr, "Error during setresgid(0): %m\n");
_exit(1);
}
if (setresuid(0, 0, 0) != 0) {
fprintf(stderr, "Error during setresuid(0): %m\n");
_exit(1);
}
}
if ((flags & ~CLONE_NEWUSER) != 0) {
if (unshare(flags & ~CLONE_NEWUSER) == -1) {
fprintf(stderr, "Error during unshare(...): %m\n");
_exit(1);
}
}
return;
}

273
unshare/unshare.go Normal file
View File

@ -0,0 +1,273 @@
// +build linux
package unshare
import (
"bytes"
"fmt"
"io"
"os"
"os/exec"
"runtime"
"strconv"
"strings"
"syscall"
"github.com/containers/storage/pkg/reexec"
"github.com/opencontainers/runtime-spec/specs-go"
"github.com/pkg/errors"
"github.com/projectatomic/buildah/util"
)
// Cmd wraps an exec.Cmd created by the reexec package in unshare(), and
// handles setting ID maps and other related settings by triggering
// initialization code in the child.
type Cmd struct {
*exec.Cmd
UnshareFlags int
UseNewuidmap bool
UidMappings []specs.LinuxIDMapping
UseNewgidmap bool
GidMappings []specs.LinuxIDMapping
GidMappingsEnableSetgroups bool
Setsid bool
Setpgrp bool
Ctty *os.File
OOMScoreAdj int
Hook func(pid int) error
}
// Command creates a new Cmd which can be customized.
func Command(args ...string) *Cmd {
cmd := reexec.Command(args...)
return &Cmd{
Cmd: cmd,
}
}
func (c *Cmd) Start() error {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
// Set an environment variable to tell the child to synchronize its startup.
if c.Env == nil {
c.Env = os.Environ()
}
c.Env = append(c.Env, fmt.Sprintf("_Buildah-unshare=%d", c.UnshareFlags))
// Create the pipe for reading the child's PID.
pidRead, pidWrite, err := os.Pipe()
if err != nil {
return errors.Wrapf(err, "error creating pid pipe")
}
c.Env = append(c.Env, fmt.Sprintf("_Buildah-pid-pipe=%d", len(c.ExtraFiles)+3))
c.ExtraFiles = append(c.ExtraFiles, pidWrite)
// Create the pipe for letting the child know to proceed.
continueRead, continueWrite, err := os.Pipe()
if err != nil {
pidRead.Close()
pidWrite.Close()
return errors.Wrapf(err, "error creating pid pipe")
}
c.Env = append(c.Env, fmt.Sprintf("_Buildah-continue-pipe=%d", len(c.ExtraFiles)+3))
c.ExtraFiles = append(c.ExtraFiles, continueRead)
// Pass along other instructions.
if c.Setsid {
c.Env = append(c.Env, "_Buildah-setsid=1")
}
if c.Setpgrp {
c.Env = append(c.Env, "_Buildah-setpgrp=1")
}
if c.Ctty != nil {
c.Env = append(c.Env, fmt.Sprintf("_Buildah-ctty=%d", len(c.ExtraFiles)+3))
c.ExtraFiles = append(c.ExtraFiles, c.Ctty)
}
if c.GidMappingsEnableSetgroups {
c.Env = append(c.Env, "_Buildah-allow-setgroups=1")
} else {
c.Env = append(c.Env, "_Buildah-allow-setgroups=0")
}
// Make sure we clean up our pipes.
defer func() {
if pidRead != nil {
pidRead.Close()
}
if pidWrite != nil {
pidWrite.Close()
}
if continueRead != nil {
continueRead.Close()
}
if continueWrite != nil {
continueWrite.Close()
}
}()
// Start the new process.
err = c.Cmd.Start()
if err != nil {
return err
}
// Close the ends of the pipes that the parent doesn't need.
continueRead.Close()
continueRead = nil
pidWrite.Close()
pidWrite = nil
// Read the child's PID from the pipe.
pidString := ""
b := new(bytes.Buffer)
io.Copy(b, pidRead)
pidString = b.String()
pid, err := strconv.Atoi(pidString)
if err != nil {
fmt.Fprintf(continueWrite, "error parsing PID %q: %v", pidString, err)
return errors.Wrapf(err, "error parsing PID %q", pidString)
}
pidString = fmt.Sprintf("%d", pid)
// If we created a new user namespace, set any specified mappings.
if c.UnshareFlags&syscall.CLONE_NEWUSER != 0 {
// Always set "setgroups".
setgroups, err := os.OpenFile(fmt.Sprintf("/proc/%s/setgroups", pidString), os.O_TRUNC|os.O_WRONLY, 0)
if err != nil {
fmt.Fprintf(continueWrite, "error opening setgroups: %v", err)
return errors.Wrapf(err, "error opening /proc/%s/setgroups", pidString)
}
defer setgroups.Close()
if c.GidMappingsEnableSetgroups {
if _, err := fmt.Fprintf(setgroups, "allow"); err != nil {
fmt.Fprintf(continueWrite, "error writing \"allow\" to setgroups: %v", err)
return errors.Wrapf(err, "error opening \"allow\" to /proc/%s/setgroups", pidString)
}
} else {
if _, err := fmt.Fprintf(setgroups, "deny"); err != nil {
fmt.Fprintf(continueWrite, "error writing \"deny\" to setgroups: %v", err)
return errors.Wrapf(err, "error writing \"deny\" to /proc/%s/setgroups", pidString)
}
}
if len(c.UidMappings) == 0 || len(c.GidMappings) == 0 {
uidmap, gidmap, err := util.GetHostIDMappings("")
if err != nil {
fmt.Fprintf(continueWrite, "error reading ID mappings in parent: %v", err)
return errors.Wrapf(err, "error reading ID mappings in parent")
}
if len(c.UidMappings) == 0 {
c.UidMappings = uidmap
for i := range c.UidMappings {
c.UidMappings[i].HostID = c.UidMappings[i].ContainerID
}
}
if len(c.GidMappings) == 0 {
c.GidMappings = gidmap
for i := range c.GidMappings {
c.GidMappings[i].HostID = c.GidMappings[i].ContainerID
}
}
}
if len(c.GidMappings) > 0 {
// Build the GID map, since writing to the proc file has to be done all at once.
g := new(bytes.Buffer)
for _, m := range c.GidMappings {
fmt.Fprintf(g, "%d %d %d\n", m.ContainerID, m.HostID, m.Size)
}
// Set the GID map.
if c.UseNewgidmap {
cmd := exec.Command("newgidmap", append([]string{pidString}, strings.Fields(strings.Replace(g.String(), "\n", " ", -1))...)...)
g.Reset()
cmd.Stdout = g
cmd.Stderr = g
err := cmd.Run()
if err != nil {
fmt.Fprintf(continueWrite, "error running newgidmap: %v: %s", err, g.String())
return errors.Wrapf(err, "error running newgidmap: %s", g.String())
}
} else {
gidmap, err := os.OpenFile(fmt.Sprintf("/proc/%s/gid_map", pidString), os.O_TRUNC|os.O_WRONLY, 0)
if err != nil {
fmt.Fprintf(continueWrite, "error opening /proc/%s/gid_map: %v", pidString, err)
return errors.Wrapf(err, "error opening /proc/%s/gid_map", pidString)
}
defer gidmap.Close()
if _, err := fmt.Fprintf(gidmap, "%s", g.String()); err != nil {
fmt.Fprintf(continueWrite, "error writing /proc/%s/gid_map: %v", pidString, err)
return errors.Wrapf(err, "error writing /proc/%s/gid_map", pidString)
}
}
}
if len(c.UidMappings) > 0 {
// Build the UID map, since writing to the proc file has to be done all at once.
u := new(bytes.Buffer)
for _, m := range c.UidMappings {
fmt.Fprintf(u, "%d %d %d\n", m.ContainerID, m.HostID, m.Size)
}
// Set the GID map.
if c.UseNewuidmap {
cmd := exec.Command("newuidmap", append([]string{pidString}, strings.Fields(strings.Replace(u.String(), "\n", " ", -1))...)...)
u.Reset()
cmd.Stdout = u
cmd.Stderr = u
err := cmd.Run()
if err != nil {
fmt.Fprintf(continueWrite, "error running newuidmap: %v: %s", err, u.String())
return errors.Wrapf(err, "error running newuidmap: %s", u.String())
}
} else {
uidmap, err := os.OpenFile(fmt.Sprintf("/proc/%s/uid_map", pidString), os.O_TRUNC|os.O_WRONLY, 0)
if err != nil {
fmt.Fprintf(continueWrite, "error opening /proc/%s/uid_map: %v", pidString, err)
return errors.Wrapf(err, "error opening /proc/%s/uid_map", pidString)
}
defer uidmap.Close()
if _, err := fmt.Fprintf(uidmap, "%s", u.String()); err != nil {
fmt.Fprintf(continueWrite, "error writing /proc/%s/uid_map: %v", pidString, err)
return errors.Wrapf(err, "error writing /proc/%s/uid_map", pidString)
}
}
}
}
// Adjust the process's OOM score.
oomScoreAdj, err := os.OpenFile(fmt.Sprintf("/proc/%s/oom_score_adj", pidString), os.O_TRUNC|os.O_WRONLY, 0)
if err != nil {
fmt.Fprintf(continueWrite, "error opening oom_score_adj: %v", err)
return errors.Wrapf(err, "error opening /proc/%s/oom_score_adj", pidString)
}
if _, err := fmt.Fprintf(oomScoreAdj, "%d\n", c.OOMScoreAdj); err != nil {
fmt.Fprintf(continueWrite, "error writing \"%d\" to oom_score_adj: %v", c.OOMScoreAdj, err)
return errors.Wrapf(err, "error writing \"%d\" to /proc/%s/oom_score_adj", c.OOMScoreAdj)
}
defer oomScoreAdj.Close()
// Run any additional setup that we want to do before the child starts running proper.
if c.Hook != nil {
if err = c.Hook(pid); err != nil {
fmt.Fprintf(continueWrite, "hook error: %v", err)
return err
}
}
return nil
}
func (c *Cmd) Run() error {
if err := c.Start(); err != nil {
return err
}
return c.Wait()
}
func (c *Cmd) CombinedOutput() ([]byte, error) {
return nil, errors.New("unshare: CombinedOutput() not implemented")
}
func (c *Cmd) Output() ([]byte, error) {
return nil, errors.New("unshare: Output() not implemented")
}

10
unshare/unshare_cgo.go Normal file
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@ -0,0 +1,10 @@
// +build linux,cgo,!gccgo
package unshare
// #cgo CFLAGS: -Wall
// extern void _buildah_unshare(void);
// void __attribute__((constructor)) init(void) {
// _buildah_unshare();
// }
import "C"

25
unshare/unshare_gccgo.go Normal file
View File

@ -0,0 +1,25 @@
// +build linux,cgo,gccgo
package unshare
// #cgo CFLAGS: -Wall -Wextra
// extern void _buildah_unshare(void);
// void __attribute__((constructor)) init(void) {
// _buildah_unshare();
// }
import "C"
// This next bit is straight out of libcontainer.
// AlwaysFalse is here to stay false
// (and be exported so the compiler doesn't optimize out its reference)
var AlwaysFalse bool
func init() {
if AlwaysFalse {
// by referencing this C init() in a noop test, it will ensure the compiler
// links in the C function.
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65134
C.init()
}
}

255
unshare/unshare_test.go Normal file
View File

@ -0,0 +1,255 @@
// +build linux
package unshare
import (
"bytes"
"encoding/json"
"io/ioutil"
"os"
"strconv"
"strings"
"syscall"
"testing"
"github.com/containers/storage/pkg/reexec"
"github.com/opencontainers/runtime-spec/specs-go"
"github.com/projectatomic/buildah/util"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
func TestMain(m *testing.M) {
if reexec.Init() {
return
}
os.Exit(m.Run())
}
func init() {
reexec.Register("report", report)
}
var (
CloneFlags = map[string]int{
"ipc": syscall.CLONE_NEWIPC,
"net": syscall.CLONE_NEWNET,
"mnt": syscall.CLONE_NEWNS,
"user": syscall.CLONE_NEWUSER,
"uts": syscall.CLONE_NEWUTS,
}
)
type Report struct {
Namespaces map[string]string
UIDMappings []specs.LinuxIDMapping
GIDMappings []specs.LinuxIDMapping
Pgrp int
Sid int
OOMScoreAdj int
}
func report() {
var report Report
report.Namespaces = make(map[string]string)
for name := range CloneFlags {
linkTarget, err := os.Readlink("/proc/self/ns/" + name)
if err != nil {
logrus.Errorf("error reading link /proc/self/ns/%s: %v", name, err)
os.Exit(1)
}
report.Namespaces[name] = linkTarget
}
report.Pgrp = syscall.Getpgrp()
sid, err := unix.Getsid(unix.Getpid())
if err != nil {
logrus.Errorf("error reading current session ID: %v", err)
os.Exit(1)
}
report.Sid = sid
oomBytes, err := ioutil.ReadFile("/proc/self/oom_score_adj")
if err != nil {
logrus.Errorf("error reading current oom_score_adj: %v", err)
os.Exit(1)
}
oomFields := strings.Fields(string(oomBytes))
if len(oomFields) != 1 {
logrus.Errorf("error parsing current oom_score_adj %q: wrong number of fields", string(oomBytes))
os.Exit(1)
}
oom, err := strconv.Atoi(oomFields[0])
if err != nil {
logrus.Errorf("error parsing current oom_score_adj %q: %v", oomFields[0], err)
os.Exit(1)
}
report.OOMScoreAdj = oom
uidmap, gidmap, err := util.GetHostIDMappings("")
if err != nil {
logrus.Errorf("error reading current ID mappings: %v", err)
os.Exit(1)
}
for _, m := range uidmap {
report.UIDMappings = append(report.UIDMappings, m)
}
for _, m := range gidmap {
report.GIDMappings = append(report.GIDMappings, m)
}
json.NewEncoder(os.Stdout).Encode(report)
}
func TestUnshareNamespaces(t *testing.T) {
for name, flag := range CloneFlags {
var report Report
buf := new(bytes.Buffer)
cmd := Command("report")
cmd.UnshareFlags = syscall.CLONE_NEWUSER | flag
cmd.UidMappings = []specs.LinuxIDMapping{{HostID: uint32(syscall.Getuid()), ContainerID: 0, Size: 1}}
cmd.GidMappings = []specs.LinuxIDMapping{{HostID: uint32(syscall.Getgid()), ContainerID: 0, Size: 1}}
cmd.Stdout = buf
cmd.Stderr = buf
err := cmd.Run()
if err != nil {
t.Fatalf("run %q: %v: %s", name, err, buf.String())
break
}
if err = json.Unmarshal(buf.Bytes(), &report); err != nil {
t.Fatalf("error parsing results: %v", err)
break
}
for ns := range CloneFlags {
linkTarget, err := os.Readlink("/proc/self/ns/" + ns)
if err != nil {
t.Fatalf("error reading link /proc/self/ns/%s: %v", ns, err)
os.Exit(1)
}
if ns == name || ns == "user" { // we always create a new user namespace
if report.Namespaces[ns] == linkTarget {
t.Fatalf("child is still in our %q namespace", name)
os.Exit(1)
}
} else {
if report.Namespaces[ns] != linkTarget {
t.Fatalf("child is not in our %q namespace", name)
os.Exit(1)
}
}
}
}
}
func TestUnsharePgrp(t *testing.T) {
for _, same := range []bool{false, true} {
var report Report
buf := new(bytes.Buffer)
cmd := Command("report")
cmd.Setpgrp = !same
cmd.Stdout = buf
cmd.Stderr = buf
err := cmd.Run()
if err != nil {
t.Fatalf("run: %v: %s", err, buf.String())
break
}
if err = json.Unmarshal(buf.Bytes(), &report); err != nil {
t.Fatalf("error parsing results: %v", err)
break
}
if (report.Pgrp == syscall.Getpgrp()) != same {
t.Fatalf("expected %d == %d to be %v", report.Pgrp, syscall.Getpgrp(), same)
}
}
}
func TestUnshareSid(t *testing.T) {
sid, err := unix.Getsid(unix.Getpid())
if err != nil {
t.Fatalf("error reading current session ID: %v", err)
}
for _, same := range []bool{false, true} {
var report Report
buf := new(bytes.Buffer)
cmd := Command("report")
cmd.Setsid = !same
cmd.Stdout = buf
cmd.Stderr = buf
err := cmd.Run()
if err != nil {
t.Fatalf("run: %v: %s", err, buf.String())
break
}
if err = json.Unmarshal(buf.Bytes(), &report); err != nil {
t.Fatalf("error parsing results: %v", err)
break
}
if (report.Sid == sid) != same {
t.Fatalf("expected %d == %d to be %v", report.Sid, sid, same)
}
}
}
func TestUnshareOOMScoreAdj(t *testing.T) {
for _, adj := range []int{0, 1, 2, 3} {
var report Report
buf := new(bytes.Buffer)
cmd := Command("report")
cmd.OOMScoreAdj = adj
cmd.Stdout = buf
cmd.Stderr = buf
err := cmd.Run()
if err != nil {
t.Fatalf("run: %v: %s", err, buf.String())
break
}
if err = json.Unmarshal(buf.Bytes(), &report); err != nil {
t.Fatalf("error parsing results: %v", err)
break
}
if report.OOMScoreAdj != adj {
t.Fatalf("saw oom_score_adj %d to be %v", adj, report.OOMScoreAdj)
}
}
}
func TestUnshareIDMappings(t *testing.T) {
var report Report
buf := new(bytes.Buffer)
cmd := Command("report")
cmd.UnshareFlags = syscall.CLONE_NEWUSER
cmd.UidMappings = []specs.LinuxIDMapping{{HostID: uint32(syscall.Getuid()), ContainerID: 0, Size: 1}}
cmd.GidMappings = []specs.LinuxIDMapping{{HostID: uint32(syscall.Getgid()), ContainerID: 0, Size: 1}}
cmd.Stdout = buf
cmd.Stderr = buf
err := cmd.Run()
if err != nil {
t.Fatalf("run: %v: %s", err, buf.String())
}
if err = json.Unmarshal(buf.Bytes(), &report); err != nil {
t.Fatalf("error parsing results: %v", err)
}
if len(cmd.UidMappings) != len(report.UIDMappings) {
t.Fatalf("set %d UID mappings, read %d instead", len(cmd.UidMappings), len(report.UIDMappings))
}
for i := range cmd.UidMappings {
if cmd.UidMappings[i].ContainerID != report.UIDMappings[i].ContainerID ||
cmd.UidMappings[i].HostID != report.UIDMappings[i].HostID ||
cmd.UidMappings[i].Size != report.UIDMappings[i].Size {
t.Fatalf("uid map entry %#v != %#v", cmd.UidMappings[i], report.UIDMappings[i])
}
}
if len(cmd.GidMappings) != len(report.GIDMappings) {
t.Fatalf("set %d GID mappings, read %d instead", len(cmd.GidMappings), len(report.GIDMappings))
}
for i := range cmd.GidMappings {
if cmd.GidMappings[i].ContainerID != report.GIDMappings[i].ContainerID ||
cmd.GidMappings[i].HostID != report.GIDMappings[i].HostID ||
cmd.GidMappings[i].Size != report.GIDMappings[i].Size {
t.Fatalf("gid map entry %#v != %#v", cmd.GidMappings[i], report.GIDMappings[i])
}
}
}

1
unshare/unshare_unsupported.go Normal file
View File

@ -0,0 +1 @@
package unshare

38
util/util.go
View File

@ -7,6 +7,7 @@ import (
"net/url"
"os"
"path"
"path/filepath"
"strconv"
"strings"
@ -330,7 +331,8 @@ func getHostIDMappings(path string) ([]specs.LinuxIDMapping, error) {
return mappings, nil
}
// GetHostIDMappings reads mappings for the current process from the kernel.
// GetHostIDMappings reads mappings for the specified process (or the current
// process if pid is "self" or an empty string) from the kernel.
func GetHostIDMappings(pid string) ([]specs.LinuxIDMapping, []specs.LinuxIDMapping, error) {
if pid == "" {
pid = "self"
@ -428,3 +430,37 @@ func ParseIDMappings(uidmap, gidmap []string) ([]idtools.IDMap, []idtools.IDMap,
}
return uid, gid, nil
}
// UnsharedRootPath returns a location under ($XDG_DATA_HOME/containers/storage,
// or $HOME/.local/share/containers/storage, or
// (the user's home directory)/.local/share/containers/storage, or an error.
func UnsharedRootPath(homedir string) (string, error) {
// If $XDG_DATA_HOME is defined...
if envDataHome, haveDataHome := os.LookupEnv("XDG_DATA_HOME"); haveDataHome {
return filepath.Join(envDataHome, "containers", "storage"), nil
}
// If $XDG_DATA_HOME is not defined, but $HOME is defined...
if envHomedir, haveHomedir := os.LookupEnv("HOME"); haveHomedir {
// Default to the user's $HOME/.local/share/containers/storage subdirectory.
return filepath.Join(envHomedir, ".local", "share", "containers", "storage"), nil
}
// If we know where our home directory is...
if homedir != "" {
// Default to the user's homedir/.local/share/containers/storage subdirectory.
return filepath.Join(homedir, ".local", "share", "containers", "storage"), nil
}
return "", errors.New("unable to determine a --root location: neither $XDG_DATA_HOME nor $HOME is set")
}
// UnsharedRunrootPath returns $XDG_RUNTIME_DIR/run, /var/run/user/(the user's UID)/run, or an error.
func UnsharedRunrootPath(uid string) (string, error) {
// If $XDG_RUNTIME_DIR is defined...
if envRuntimeDir, haveRuntimeDir := os.LookupEnv("XDG_RUNTIME_DIR"); haveRuntimeDir {
return filepath.Join(envRuntimeDir, "run"), nil
}
// If $XDG_RUNTIME_DIR is not defined, but we know our UID...
if uid != "" {
return filepath.Join("/var/run/user", uid, "run"), nil
}
return "", errors.New("unable to determine a --runroot location: $XDG_RUNTIME_DIR is not set, and we don't know our UID")
}