pkg/util: add helper function to configure timezone for pod/containers

This PR consolidates common functionality used by CRI-O and Podman
in one central location. I aimed to keep this change more generic,
considering that CRI-O and Podman have different ways for the file
mounting and applying security labels.

Signed-off-by: Sohan Kunkerkar <sohank2602@gmail.com>

pkg/util/util.go

@@ -1,16 +1,102 @@
 package util
 
 import (
+	"errors"
 	"fmt"
+	"io"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"regexp"
 	"time"
 
+	securejoin "github.com/cyphar/filepath-securejoin"
 	"github.com/fsnotify/fsnotify"
 	"github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
 )
 
+// ConfigureContainerTimeZone configure the time zone for a container.
+// It returns the path of the created /etc/localtime file if needed.
+func ConfigureContainerTimeZone(timezone, containerRunDir, mountPoint, etcPath, mountLabel, containerID string) (string, error) {
+	if timezone == "" {
+		return "", nil
+	}
+	var err error
+	timezonePath := filepath.Join("/usr/share/zoneinfo", timezone)
+	if timezone == "local" {
+		timezonePath, err = filepath.EvalSymlinks("/etc/localtime")
+		if err != nil {
+			return "", fmt.Errorf("finding local timezone for container %s: %w", containerID, err)
+		}
+	}
+
+	etcFd, err := unix.Open(etcPath, unix.O_RDONLY|unix.O_PATH, 0)
+	if err != nil {
+		return "", fmt.Errorf("open /etc in the container: %w", err)
+	}
+	defer unix.Close(etcFd)
+
+	// Make sure to remove any existing localtime file in the container to not create invalid links
+	err = unix.Unlinkat(etcFd, "localtime", 0)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return "", fmt.Errorf("removing /etc/localtime: %w", err)
+	}
+
+	hostPath, err := securejoin.SecureJoin(mountPoint, timezonePath)
+	if err != nil {
+		return "", fmt.Errorf("resolve zoneinfo path in the container: %w", err)
+	}
+
+	if _, err := os.Stat(hostPath); err != nil {
+		// File does not exist, which means tzdata is not installed in the container.
+		// Create /etc/localtime as a copy from the host.
+		logrus.Debugf("Timezone %s does not exist in the container, create our own copy from the host", timezonePath)
+		localtimePath, err := copyTimezoneFile(containerRunDir, mountLabel, timezonePath)
+		if err != nil {
+			return "", fmt.Errorf("setting timezone for container %s: %w", containerID, err)
+		}
+		return localtimePath, nil
+	} else {
+		// File exists, let's create a symlink according to localtime(5)
+		logrus.Debugf("Create localtime symlink for %s", timezonePath)
+		err = unix.Symlinkat(hostPath, etcFd, "localtime")
+		if err != nil {
+			return "", fmt.Errorf("creating /etc/localtime symlink: %w", err)
+		}
+	}
+	return "", nil
+}
+
+// copyTimezoneFile copies the timezone file from the host to the container.
+func copyTimezoneFile(containerRunDir, mountLabel, zonePath string) (string, error) {
+	localtimeCopy := filepath.Join(containerRunDir, "localtime")
+	file, err := os.Stat(zonePath)
+	if err != nil {
+		return "", err
+	}
+	if file.IsDir() {
+		return "", errors.New("invalid timezone: is a directory")
+	}
+	src, err := os.Open(zonePath)
+	if err != nil {
+		return "", err
+	}
+	defer src.Close()
+
+	dest, err := os.Create(localtimeCopy)
+	if err != nil {
+		return "", err
+	}
+	defer dest.Close()
+
+	_, err = io.Copy(dest, src)
+	if err != nil {
+		return "", err
+	}
+	return localtimeCopy, err
+}
+
 // StringInSlice determines if a string is in a string slice, returns bool
 func StringInSlice(s string, sl []string) bool {
 	for _, i := range sl {