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|
//go:build linux && cgo
// +build linux,cgo
package rootless
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"os"
"os/exec"
gosignal "os/signal"
"os/user"
"runtime"
"strconv"
"strings"
"sync"
"unsafe"
"github.com/containers/podman/v4/pkg/errorhandling"
"github.com/containers/storage/pkg/idtools"
pmount "github.com/containers/storage/pkg/mount"
"github.com/containers/storage/pkg/unshare"
"github.com/sirupsen/logrus"
"github.com/syndtr/gocapability/capability"
"golang.org/x/sys/unix"
)
/*
#cgo remote CFLAGS: -Wall -Werror -DDISABLE_JOIN_SHORTCUT
#include <stdlib.h>
#include <sys/types.h>
extern uid_t rootless_uid();
extern uid_t rootless_gid();
extern int reexec_in_user_namespace(int ready, char *pause_pid_file_path, char *file_to_read, int fd);
extern int reexec_in_user_namespace_wait(int pid, int options);
extern int reexec_userns_join(int pid, char *pause_pid_file_path);
extern int is_fd_inherited(int fd);
*/
import "C"
const (
numSig = 65 // max number of signals
)
func runInUser() error {
return os.Setenv("_CONTAINERS_USERNS_CONFIGURED", "done")
}
var (
isRootlessOnce sync.Once
isRootless bool
)
// IsRootless tells us if we are running in rootless mode
func IsRootless() bool {
isRootlessOnce.Do(func() {
rootlessUIDInit := int(C.rootless_uid())
rootlessGIDInit := int(C.rootless_gid())
if rootlessUIDInit != 0 {
// This happens if we joined the user+mount namespace as part of
if err := os.Setenv("_CONTAINERS_USERNS_CONFIGURED", "done"); err != nil {
logrus.Errorf("Failed to set environment variable %s as %s", "_CONTAINERS_USERNS_CONFIGURED", "done")
}
if err := os.Setenv("_CONTAINERS_ROOTLESS_UID", fmt.Sprintf("%d", rootlessUIDInit)); err != nil {
logrus.Errorf("Failed to set environment variable %s as %d", "_CONTAINERS_ROOTLESS_UID", rootlessUIDInit)
}
if err := os.Setenv("_CONTAINERS_ROOTLESS_GID", fmt.Sprintf("%d", rootlessGIDInit)); err != nil {
logrus.Errorf("Failed to set environment variable %s as %d", "_CONTAINERS_ROOTLESS_GID", rootlessGIDInit)
}
}
isRootless = os.Geteuid() != 0 || os.Getenv("_CONTAINERS_USERNS_CONFIGURED") != ""
if !isRootless {
hasCapSysAdmin, err := unshare.HasCapSysAdmin()
if err != nil {
logrus.Warnf("Failed to read CAP_SYS_ADMIN presence for the current process")
}
if err == nil && !hasCapSysAdmin {
isRootless = true
}
}
})
return isRootless
}
// GetRootlessUID returns the UID of the user in the parent userNS
func GetRootlessUID() int {
uidEnv := os.Getenv("_CONTAINERS_ROOTLESS_UID")
if uidEnv != "" {
u, _ := strconv.Atoi(uidEnv)
return u
}
return os.Geteuid()
}
// GetRootlessGID returns the GID of the user in the parent userNS
func GetRootlessGID() int {
gidEnv := os.Getenv("_CONTAINERS_ROOTLESS_GID")
if gidEnv != "" {
u, _ := strconv.Atoi(gidEnv)
return u
}
/* If the _CONTAINERS_ROOTLESS_UID is set, assume the gid==uid. */
uidEnv := os.Getenv("_CONTAINERS_ROOTLESS_UID")
if uidEnv != "" {
u, _ := strconv.Atoi(uidEnv)
return u
}
return os.Getegid()
}
func tryMappingTool(uid bool, pid int, hostID int, mappings []idtools.IDMap) error {
var tool = "newuidmap"
mode := os.ModeSetuid
cap := capability.CAP_SETUID
idtype := "setuid"
if !uid {
tool = "newgidmap"
mode = os.ModeSetgid
cap = capability.CAP_SETGID
idtype = "setgid"
}
path, err := exec.LookPath(tool)
if err != nil {
return fmt.Errorf("command required for rootless mode with multiple IDs: %w", err)
}
appendTriplet := func(l []string, a, b, c int) []string {
return append(l, strconv.Itoa(a), strconv.Itoa(b), strconv.Itoa(c))
}
args := []string{path, fmt.Sprintf("%d", pid)}
args = appendTriplet(args, 0, hostID, 1)
for _, i := range mappings {
if hostID >= i.HostID && hostID < i.HostID+i.Size {
what := "UID"
where := "/etc/subuid"
if !uid {
what = "GID"
where = "/etc/subgid"
}
return fmt.Errorf("invalid configuration: the specified mapping %d:%d in %q includes the user %s", i.HostID, i.Size, where, what)
}
args = appendTriplet(args, i.ContainerID+1, i.HostID, i.Size)
}
cmd := exec.Cmd{
Path: path,
Args: args,
}
if output, err := cmd.CombinedOutput(); err != nil {
logrus.Errorf("running `%s`: %s", strings.Join(args, " "), output)
errorStr := fmt.Sprintf("cannot set up namespace using %q", path)
if isSet, err := unshare.IsSetID(cmd.Path, mode, cap); err != nil {
logrus.Errorf("Failed to check for %s on %s: %v", idtype, path, err)
} else if !isSet {
errorStr = fmt.Sprintf("%s: should have %s or have filecaps %s", errorStr, idtype, idtype)
}
return fmt.Errorf("%v: %w", errorStr, err)
}
return nil
}
// joinUserAndMountNS re-exec podman in a new userNS and join the user and mount
// namespace of the specified PID without looking up its parent. Useful to join directly
// the conmon process.
func joinUserAndMountNS(pid uint, pausePid string) (bool, int, error) {
hasCapSysAdmin, err := unshare.HasCapSysAdmin()
if err != nil {
return false, 0, err
}
if hasCapSysAdmin || os.Getenv("_CONTAINERS_USERNS_CONFIGURED") != "" {
return false, 0, nil
}
cPausePid := C.CString(pausePid)
defer C.free(unsafe.Pointer(cPausePid))
pidC := C.reexec_userns_join(C.int(pid), cPausePid)
if int(pidC) < 0 {
return false, -1, fmt.Errorf("cannot re-exec process to join the existing user namespace")
}
ret := C.reexec_in_user_namespace_wait(pidC, 0)
if ret < 0 {
return false, -1, errors.New("waiting for the re-exec process")
}
return true, int(ret), nil
}
// GetConfiguredMappings returns the additional IDs configured for the current user.
func GetConfiguredMappings() ([]idtools.IDMap, []idtools.IDMap, error) {
var uids, gids []idtools.IDMap
username := os.Getenv("USER")
if username == "" {
var id string
if os.Geteuid() == 0 {
id = strconv.Itoa(GetRootlessUID())
} else {
id = strconv.Itoa(os.Geteuid())
}
userID, err := user.LookupId(id)
if err == nil {
username = userID.Username
}
}
mappings, err := idtools.NewIDMappings(username, username)
if err != nil {
logLevel := logrus.ErrorLevel
if os.Geteuid() == 0 && GetRootlessUID() == 0 {
logLevel = logrus.DebugLevel
}
logrus.StandardLogger().Logf(logLevel, "cannot find UID/GID for user %s: %v - check rootless mode in man pages.", username, err)
} else {
uids = mappings.UIDs()
gids = mappings.GIDs()
}
return uids, gids, nil
}
func copyMappings(from, to string) error {
content, err := ioutil.ReadFile(from)
if err != nil {
return err
}
// Both runc and crun check whether the current process is in a user namespace
// by looking up 4294967295 in /proc/self/uid_map. If the mappings would be
// copied as they are, the check in the OCI runtimes would fail. So just split
// it in two different ranges.
if bytes.Contains(content, []byte("4294967295")) {
content = []byte("0 0 1\n1 1 4294967294\n")
}
return ioutil.WriteFile(to, content, 0600)
}
func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (_ bool, _ int, retErr error) {
hasCapSysAdmin, err := unshare.HasCapSysAdmin()
if err != nil {
return false, 0, err
}
if hasCapSysAdmin || os.Getenv("_CONTAINERS_USERNS_CONFIGURED") != "" {
if os.Getenv("_CONTAINERS_USERNS_CONFIGURED") == "init" {
return false, 0, runInUser()
}
return false, 0, nil
}
if _, inContainer := os.LookupEnv("container"); !inContainer {
if mounts, err := pmount.GetMounts(); err == nil {
for _, m := range mounts {
if m.Mountpoint == "/" {
isShared := false
for _, o := range strings.Split(m.Optional, ",") {
if strings.HasPrefix(o, "shared:") {
isShared = true
break
}
}
if !isShared {
logrus.Warningf("%q is not a shared mount, this could cause issues or missing mounts with rootless containers", m.Mountpoint)
}
break
}
}
}
}
cPausePid := C.CString(pausePid)
defer C.free(unsafe.Pointer(cPausePid))
cFileToRead := C.CString(fileToRead)
defer C.free(unsafe.Pointer(cFileToRead))
var fileOutputFD C.int
if fileOutput != nil {
fileOutputFD = C.int(fileOutput.Fd())
}
runtime.LockOSThread()
defer runtime.UnlockOSThread()
fds, err := unix.Socketpair(unix.AF_UNIX, unix.SOCK_DGRAM, 0)
if err != nil {
return false, -1, err
}
r, w := os.NewFile(uintptr(fds[0]), "sync host"), os.NewFile(uintptr(fds[1]), "sync child")
var pid int
defer errorhandling.CloseQuiet(r)
defer errorhandling.CloseQuiet(w)
defer func() {
toWrite := []byte("0")
if retErr != nil {
toWrite = []byte("1")
}
if _, err := w.Write(toWrite); err != nil {
logrus.Errorf("Failed to write byte 0: %q", err)
}
if retErr != nil && pid > 0 {
if err := unix.Kill(pid, unix.SIGKILL); err != nil {
if err != unix.ESRCH {
logrus.Errorf("Failed to clean up process %d: %v", pid, err)
}
}
C.reexec_in_user_namespace_wait(C.int(pid), 0)
}
}()
pidC := C.reexec_in_user_namespace(C.int(r.Fd()), cPausePid, cFileToRead, fileOutputFD)
pid = int(pidC)
if pid < 0 {
return false, -1, fmt.Errorf("cannot re-exec process")
}
uids, gids, err := GetConfiguredMappings()
if err != nil {
return false, -1, err
}
uidMap := fmt.Sprintf("/proc/%d/uid_map", pid)
gidMap := fmt.Sprintf("/proc/%d/gid_map", pid)
uidsMapped := false
if err := copyMappings("/proc/self/uid_map", uidMap); err == nil {
uidsMapped = true
}
if uids != nil && !uidsMapped {
err := tryMappingTool(true, pid, os.Geteuid(), uids)
// If some mappings were specified, do not ignore the error
if err != nil && len(uids) > 0 {
return false, -1, err
}
uidsMapped = err == nil
}
if !uidsMapped {
logrus.Warnf("Using rootless single mapping into the namespace. This might break some images. Check /etc/subuid and /etc/subgid for adding sub*ids if not using a network user")
setgroups := fmt.Sprintf("/proc/%d/setgroups", pid)
err = ioutil.WriteFile(setgroups, []byte("deny\n"), 0666)
if err != nil {
return false, -1, fmt.Errorf("cannot write setgroups file: %w", err)
}
logrus.Debugf("write setgroups file exited with 0")
err = ioutil.WriteFile(uidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Geteuid())), 0666)
if err != nil {
return false, -1, fmt.Errorf("cannot write uid_map: %w", err)
}
logrus.Debugf("write uid_map exited with 0")
}
gidsMapped := false
if err := copyMappings("/proc/self/gid_map", gidMap); err == nil {
gidsMapped = true
}
if gids != nil && !gidsMapped {
err := tryMappingTool(false, pid, os.Getegid(), gids)
// If some mappings were specified, do not ignore the error
if err != nil && len(gids) > 0 {
return false, -1, err
}
gidsMapped = err == nil
}
if !gidsMapped {
err = ioutil.WriteFile(gidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Getegid())), 0666)
if err != nil {
return false, -1, fmt.Errorf("cannot write gid_map: %w", err)
}
}
_, err = w.Write([]byte("0"))
if err != nil {
return false, -1, fmt.Errorf("write to sync pipe: %w", err)
}
b := make([]byte, 1)
_, err = w.Read(b)
if err != nil {
return false, -1, fmt.Errorf("read from sync pipe: %w", err)
}
if fileOutput != nil {
ret := C.reexec_in_user_namespace_wait(pidC, 0)
if ret < 0 {
return false, -1, errors.New("waiting for the re-exec process")
}
return true, 0, nil
}
if b[0] == '2' {
// We have lost the race for writing the PID file, as probably another
// process created a namespace and wrote the PID.
// Try to join it.
data, err := ioutil.ReadFile(pausePid)
if err == nil {
var pid uint64
pid, err = strconv.ParseUint(string(data), 10, 0)
if err == nil {
return joinUserAndMountNS(uint(pid), "")
}
}
return false, -1, fmt.Errorf("setting up the process: %w", err)
}
if b[0] != '0' {
return false, -1, errors.New("setting up the process")
}
signals := []os.Signal{}
for sig := 0; sig < numSig; sig++ {
if sig == int(unix.SIGTSTP) {
continue
}
signals = append(signals, unix.Signal(sig))
}
c := make(chan os.Signal, len(signals))
gosignal.Notify(c, signals...)
defer gosignal.Reset()
go func() {
for s := range c {
if s == unix.SIGCHLD || s == unix.SIGPIPE {
continue
}
if err := unix.Kill(int(pidC), s.(unix.Signal)); err != nil {
if err != unix.ESRCH {
logrus.Errorf("Failed to propagate signal to child process %d: %v", int(pidC), err)
}
}
}
}()
ret := C.reexec_in_user_namespace_wait(pidC, 0)
if ret < 0 {
return false, -1, errors.New("waiting for the re-exec process")
}
return true, int(ret), nil
}
// BecomeRootInUserNS re-exec podman in a new userNS. It returns whether podman was re-executed
// into a new user namespace and the return code from the re-executed podman process.
// If podman was re-executed the caller needs to propagate the error code returned by the child
// process.
func BecomeRootInUserNS(pausePid string) (bool, int, error) {
return becomeRootInUserNS(pausePid, "", nil)
}
// TryJoinFromFilePaths attempts to join the namespaces of the pid files in paths.
// This is useful when there are already running containers and we
// don't have a pause process yet. We can use the paths to the conmon
// processes to attempt joining their namespaces.
// If needNewNamespace is set, the file is read from a temporary user
// namespace, this is useful for containers that are running with a
// different uidmap and the unprivileged user has no way to read the
// file owned by the root in the container.
func TryJoinFromFilePaths(pausePidPath string, needNewNamespace bool, paths []string) (bool, int, error) {
var lastErr error
var pausePid int
for _, path := range paths {
if !needNewNamespace {
data, err := ioutil.ReadFile(path)
if err != nil {
lastErr = err
continue
}
pausePid, err = strconv.Atoi(string(data))
if err != nil {
lastErr = fmt.Errorf("cannot parse file %q: %w", path, err)
continue
}
} else {
r, w, err := os.Pipe()
if err != nil {
lastErr = err
continue
}
defer errorhandling.CloseQuiet(r)
if _, _, err := becomeRootInUserNS("", path, w); err != nil {
w.Close()
lastErr = err
continue
}
if err := w.Close(); err != nil {
return false, 0, err
}
defer func() {
C.reexec_in_user_namespace_wait(-1, 0)
}()
b := make([]byte, 32)
n, err := r.Read(b)
if err != nil {
lastErr = fmt.Errorf("cannot read %q: %w", path, err)
continue
}
pausePid, err = strconv.Atoi(string(b[:n]))
if err != nil {
lastErr = err
continue
}
}
if pausePid > 0 && unix.Kill(pausePid, 0) == nil {
joined, pid, err := joinUserAndMountNS(uint(pausePid), pausePidPath)
if err == nil {
return joined, pid, nil
}
lastErr = err
}
}
if lastErr != nil {
return false, 0, lastErr
}
return false, 0, fmt.Errorf("could not find any running process: %w", unix.ESRCH)
}
// ReadMappingsProc parses and returns the ID mappings at the specified path.
func ReadMappingsProc(path string) ([]idtools.IDMap, error) {
file, err := os.Open(path)
if err != nil {
return nil, err
}
defer file.Close()
mappings := []idtools.IDMap{}
buf := bufio.NewReader(file)
for {
line, _, err := buf.ReadLine()
if err != nil {
if err == io.EOF {
return mappings, nil
}
return nil, fmt.Errorf("cannot read line from %s: %w", path, err)
}
if line == nil {
return mappings, nil
}
containerID, hostID, size := 0, 0, 0
if _, err := fmt.Sscanf(string(line), "%d %d %d", &containerID, &hostID, &size); err != nil {
return nil, fmt.Errorf("cannot parse %s: %w", string(line), err)
}
mappings = append(mappings, idtools.IDMap{ContainerID: containerID, HostID: hostID, Size: size})
}
}
func matches(id int, configuredIDs []idtools.IDMap, currentIDs []idtools.IDMap) bool {
// The first mapping is the host user, handle it separately.
if currentIDs[0].HostID != id || currentIDs[0].Size != 1 {
return false
}
currentIDs = currentIDs[1:]
if len(currentIDs) != len(configuredIDs) {
return false
}
// It is fine to iterate sequentially as both slices are sorted.
for i := range currentIDs {
if currentIDs[i].HostID != configuredIDs[i].HostID {
return false
}
if currentIDs[i].Size != configuredIDs[i].Size {
return false
}
}
return true
}
// ConfigurationMatches checks whether the additional uids/gids configured for the user
// match the current user namespace.
func ConfigurationMatches() (bool, error) {
if !IsRootless() || os.Geteuid() != 0 {
return true, nil
}
uids, gids, err := GetConfiguredMappings()
if err != nil {
return false, err
}
currentUIDs, err := ReadMappingsProc("/proc/self/uid_map")
if err != nil {
return false, err
}
if !matches(GetRootlessUID(), uids, currentUIDs) {
return false, err
}
currentGIDs, err := ReadMappingsProc("/proc/self/gid_map")
if err != nil {
return false, err
}
return matches(GetRootlessGID(), gids, currentGIDs), nil
}
// IsFdInherited checks whether the fd is opened and valid to use
func IsFdInherited(fd int) bool {
return int(C.is_fd_inherited(C.int(fd))) > 0
}
|