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// +build linux
package rootless
import (
"fmt"
"io/ioutil"
"os"
"os/exec"
gosignal "os/signal"
"runtime"
"strconv"
"syscall"
"github.com/containers/storage/pkg/idtools"
"github.com/docker/docker/pkg/signal"
"github.com/pkg/errors"
)
/*
extern int reexec_in_user_namespace(int ready);
extern int reexec_in_user_namespace_wait(int pid);
*/
import "C"
func runInUser() error {
os.Setenv("_LIBPOD_USERNS_CONFIGURED", "done")
return nil
}
// IsRootless tells us if we are running in rootless mode
func IsRootless() bool {
return os.Getuid() != 0 || os.Getenv("_LIBPOD_USERNS_CONFIGURED") != ""
}
// GetRootlessUID returns the UID of the user in the parent userNS
func GetRootlessUID() int {
uidEnv := os.Getenv("_LIBPOD_ROOTLESS_UID")
if uidEnv != "" {
u, _ := strconv.Atoi(uidEnv)
return u
}
return os.Getuid()
}
func tryMappingTool(tool string, pid int, hostID int, mappings []idtools.IDMap) error {
path, err := exec.LookPath(tool)
if err != nil {
return err
}
appendTriplet := func(l []string, a, b, c int) []string {
return append(l, fmt.Sprintf("%d", a), fmt.Sprintf("%d", b), fmt.Sprintf("%d", c))
}
args := []string{path, fmt.Sprintf("%d", pid)}
args = appendTriplet(args, 0, hostID, 1)
if mappings != nil {
for _, i := range mappings {
args = appendTriplet(args, i.ContainerID+1, i.HostID, i.Size)
}
}
cmd := exec.Cmd{
Path: path,
Args: args,
}
return cmd.Run()
}
// 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() (bool, int, error) {
if os.Getuid() == 0 || os.Getenv("_LIBPOD_USERNS_CONFIGURED") != "" {
if os.Getenv("_LIBPOD_USERNS_CONFIGURED") == "init" {
return false, 0, runInUser()
}
return false, 0, nil
}
runtime.LockOSThread()
defer runtime.UnlockOSThread()
r, w, err := os.Pipe()
if err != nil {
return false, -1, err
}
defer r.Close()
defer w.Close()
pidC := C.reexec_in_user_namespace(C.int(r.Fd()))
pid := int(pidC)
if pid < 0 {
return false, -1, errors.Errorf("cannot re-exec process")
}
setgroups := fmt.Sprintf("/proc/%d/setgroups", pid)
err = ioutil.WriteFile(setgroups, []byte("deny\n"), 0666)
if err != nil {
return false, -1, errors.Wrapf(err, "cannot write setgroups file")
}
var uids, gids []idtools.IDMap
username := os.Getenv("USER")
mappings, err := idtools.NewIDMappings(username, username)
if err != nil && os.Getenv("PODMAN_ALLOW_SINGLE_ID_MAPPING_IN_USERNS") == "" {
return false, -1, err
}
if err == nil {
uids = mappings.UIDs()
gids = mappings.GIDs()
}
uidsMapped := false
if mappings != nil && uids != nil {
uidsMapped = tryMappingTool("newuidmap", pid, os.Getuid(), uids) == nil
}
if !uidsMapped {
uidMap := fmt.Sprintf("/proc/%d/uid_map", pid)
err = ioutil.WriteFile(uidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Getuid())), 0666)
if err != nil {
return false, -1, errors.Wrapf(err, "cannot write uid_map")
}
}
gidsMapped := false
if mappings != nil && gids != nil {
gidsMapped = tryMappingTool("newgidmap", pid, os.Getgid(), gids) == nil
}
if !gidsMapped {
gidMap := fmt.Sprintf("/proc/%d/gid_map", pid)
err = ioutil.WriteFile(gidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Getgid())), 0666)
if err != nil {
return false, -1, errors.Wrapf(err, "cannot write gid_map")
}
}
_, err = w.Write([]byte("1"))
if err != nil {
return false, -1, errors.Wrapf(err, "write to sync pipe")
}
c := make(chan os.Signal, 1)
gosignal.Notify(c)
defer gosignal.Reset()
go func() {
for s := range c {
if s == signal.SIGCHLD || s == signal.SIGPIPE {
continue
}
syscall.Kill(int(pidC), s.(syscall.Signal))
}
}()
ret := C.reexec_in_user_namespace_wait(pidC)
if ret < 0 {
return false, -1, errors.Wrapf(err, "error waiting for the re-exec process")
}
return true, int(ret), nil
}
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