libpod: create /etc/mtab safely
make sure the /etc/mtab symlink is created inside the rootfs when /etc
is a symlink.
Closes:
[NO NEW TESTS NEEDED] there is already a test case
@@ -39,6 +39,7 @@ import (
"github.com/opencontainers/selinux/go-selinux/label"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
+ "golang.org/x/sys/unix"
)
const (
@@ -1592,14 +1593,49 @@ func (c *Container) mountStorage() (_ string, deferredErr error) {
}()
}
+ rootUID, rootGID := c.RootUID(), c.RootGID()
+
+ dirfd, err := unix.Open(mountPoint, unix.O_RDONLY|unix.O_PATH, 0)
+ if err != nil {
+ return "", errors.Wrap(err, "open mount point")
+ }
+ defer unix.Close(dirfd)
+
+ err = unix.Mkdirat(dirfd, "etc", 0755)
+ if err != nil && !os.IsExist(err) {
+ return "", errors.Wrap(err, "create /etc")
+ }
+ // If the etc directory was created, chown it to root in the container
+ if err == nil && (rootUID != 0 || rootGID != 0) {
+ err = unix.Fchownat(dirfd, "etc", rootUID, rootGID, unix.AT_SYMLINK_NOFOLLOW)
+ if err != nil {
+ return "", errors.Wrap(err, "chown /etc")
+ }
+ }
+
+ etcInTheContainerPath, err := securejoin.SecureJoin(mountPoint, "etc")
+ if err != nil {
+ return "", errors.Wrap(err, "resolve /etc in the container")
+ }
+
+ etcInTheContainerFd, err := unix.Open(etcInTheContainerPath, unix.O_RDONLY|unix.O_PATH, 0)
+ if err != nil {
+ return "", errors.Wrap(err, "open /etc in the container")
+ }
+ defer unix.Close(etcInTheContainerFd)
+
// If /etc/mtab does not exist in container image, then we need to
// create it, so that mount command within the container will work.
- mtab := filepath.Join(mountPoint, "/etc/mtab")
- if err := idtools.MkdirAllAs(filepath.Dir(mtab), 0755, c.RootUID(), c.RootGID()); err != nil {
- return "", errors.Wrap(err, "error creating mtab directory")
+ err = unix.Symlinkat("/proc/mounts", etcInTheContainerFd, "mtab")
+ if err != nil && !os.IsExist(err) {
+ return "", errors.Wrap(err, "creating /etc/mtab symlink")
+ }
+ // If the symlink was created, then also chown it to root in the container
+ if err == nil && (rootUID != 0 || rootGID != 0) {
+ err = unix.Fchownat(etcInTheContainerFd, "mtab", rootUID, rootGID, unix.AT_SYMLINK_NOFOLLOW)
+ if err != nil {
+ return "", errors.Wrap(err, "chown /etc/mtab")
}
- if err = os.Symlink("/proc/mounts", mtab); err != nil && !os.IsExist(err) {
- return "", err
}
// Request a mount of all named volumes
