Add rootless package from containers/libpod

Add rootless package to kata in order to include some rootless
functionalities including: 1. Determining whether an exectution is
being ran rootless or not, 2. Get the rootless UID of a process,
and 3. Get the rootless runtime directory for nonroot users.

Signed-off-by: Gabi Beyer <[email protected]>

pkg/rootless/rootless.c

@@ -0,0 +1,18 @@
+#define _GNU_SOURCE
+#include <sys/types.h>
+
+static uid_t rootless_uid_init;
+static gid_t rootless_gid_init;
+
+uid_t
+rootless_uid ()
+{
+  return rootless_uid_init;
+}
+
+uid_t
+rootless_gid ()
+{
+  return rootless_gid_init;
+}
+

pkg/rootless/rootless.go

@@ -0,0 +1,98 @@
+package rootless
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"sync"
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+/*
+#include <sys/types.h>
+extern uid_t rootless_uid();
+extern uid_t rootless_gid();
+*/
+import "C"
+
+var (
+	isRootlessOnce sync.Once
+	isRootless     bool
+
+	rootlessRuntimeDirOnce sync.Once
+	rootlessRuntimeDir     string
+)
+
+// 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
+			os.Setenv("_CONTAINERS_USERNS_CONFIGURED", "done")
+			os.Setenv("_CONTAINERS_ROOTLESS_UID", fmt.Sprintf("%d", rootlessUIDInit))
+			os.Setenv("_CONTAINERS_ROOTLESS_GID", fmt.Sprintf("%d", rootlessGIDInit))
+		}
+		isRootless = os.Geteuid() != 0 || os.Getenv("_CONTAINERS_USERNS_CONFIGURED") != ""
+	})
+	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()
+}
+
+// GetRootlessRuntimeDir returns the runtime directory when running as non root
+func GetRootlessRuntimeDir() (string, error) {
+	var rootlessRuntimeDirError error
+
+	rootlessRuntimeDirOnce.Do(func() {
+		runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
+		uid := fmt.Sprintf("%d", GetRootlessUID())
+		if runtimeDir == "" {
+			tmpDir := filepath.Join("/run", "user", uid)
+			os.MkdirAll(tmpDir, 0700)
+			st, err := os.Stat(tmpDir)
+			if err == nil && int(st.Sys().(*syscall.Stat_t).Uid) == os.Geteuid() && st.Mode().Perm() == 0700 {
+				runtimeDir = tmpDir
+			}
+		}
+		if runtimeDir == "" {
+			tmpDir := filepath.Join(os.TempDir(), fmt.Sprintf("run-%s", uid))
+			os.MkdirAll(tmpDir, 0700)
+			st, err := os.Stat(tmpDir)
+			if err == nil && int(st.Sys().(*syscall.Stat_t).Uid) == os.Geteuid() && st.Mode().Perm() == 0700 {
+				runtimeDir = tmpDir
+			}
+		}
+		if runtimeDir == "" {
+			home := os.Getenv("HOME")
+			if home == "" {
+				rootlessRuntimeDirError = fmt.Errorf("neither XDG_RUNTIME_DIR nor HOME was set non-empty")
+				return
+			}
+			resolvedHome, err := filepath.EvalSymlinks(home)
+			if err != nil {
+				rootlessRuntimeDirError = errors.Wrapf(err, "cannot resolve %s", home)
+				return
+			}
+			runtimeDir = filepath.Join(resolvedHome, "rundir")
+		}
+		rootlessRuntimeDir = runtimeDir
+	})
+
+	if rootlessRuntimeDirError != nil {
+		return "", rootlessRuntimeDirError
+	}
+	return rootlessRuntimeDir, nil
+}