lorax: Move default tmp dir to /var/tmp/lorax

If systemd's tmpfiles.d timer is executed while lorax is running it will
remove any files and directories older than 30 days. This is what has
been causing the occasional error where /proc/ would seem to vanish
during the install.

Upstream has proposed this solution, https://github.com/systemd/systemd/pull/11482
but until that is released we need a work-around to protect the lorax
files.

This commit does several things:

* Move the default tmpdir from /var/tmp/ to /var/tmp/lorax/
* Add a lorax.conf tmpfiles.d file that prevents systemd-tmpfiles from
  removing anything under /var/tmp/lorax/
* Add an exit handler to lorax so that temporary directories are removed on
  exit or on a python traceback.
* Use flock to lock access to the tempdir while lorax is running.
* Remove any unlocked tempdirs named /var/tmp/lorax/lorax.* at startup

Note that the exit handler will not remove the tempdir if lorax is
killed with a signal -- those are being caught by dnf and prevent the
exit handler from running.

systemd-tmpfiles cannot clean up the tempdirs at boot time because they
contain files labeled as shadow_t, so we have to remove those when lorax
runs. It uses the flock to prevent removing any directories created by
parallel instances of lorax and only removes ones that are unlocked.
Worst case they will be around until the first run of lorax after a
reboot.

If you want to keep the working directory around for debugging purposes
use --workdir /var/tmp/lorax/my-workdir and it won't be removed by
lorax.

Resolves: rhbz#1668408

lorax.spec

@@ -205,6 +205,7 @@ getent passwd weldr >/dev/null 2>&1 || useradd -r -g weldr -d / -s /sbin/nologin
 %config(noreplace) %{_sysconfdir}/lorax/lorax.conf
 %dir %{_datadir}/lorax
 %{_mandir}/man1/*.1*
+%{_tmpfilesdir}/lorax.conf
 
 %files lmc-virt
 

setup.py

@@ -10,7 +10,8 @@ data_files = [("/etc/lorax", ["etc/lorax.conf"]),
               ("/etc/lorax", ["etc/composer.conf"]),
               ("/usr/lib/systemd/system", ["systemd/lorax-composer.service",
                                            "systemd/lorax-composer.socket"]),
-              ("/usr/lib/tmpfiles.d/", ["systemd/lorax-composer.conf"])]
+              ("/usr/lib/tmpfiles.d/", ["systemd/lorax-composer.conf",
+                                        "systemd/lorax.conf"])]
 
 # shared files
 for root, dnames, fnames in os.walk("share"):

src/pylorax/cmdline.py

@@ -75,12 +75,12 @@ def lorax_parser(dracut_default=""):
                         action="store_false", default=True, dest="doupgrade")
     optional.add_argument("--logfile", default="./lorax.log", type=os.path.abspath,
                         help="Path to logfile")
-    optional.add_argument("--tmp", default="/var/tmp",
+    optional.add_argument("--tmp", default="/var/tmp/lorax",
                         help="Top level temporary directory" )
     optional.add_argument("--cachedir", default=None, type=os.path.abspath,
                         help="DNF cache directory. Default is a temporary dir.")
     optional.add_argument("--workdir", default=None, type=os.path.abspath,
-                        help="Work directory, overrides --tmp. Default is a temporary dir under /var/tmp")
+                        help="Work directory, overrides --tmp. Default is a temporary dir under /var/tmp/lorax")
     optional.add_argument("--force", default=False, action="store_true",
                         help="Run even when the destination directory exists")
     optional.add_argument("--add-template", dest="add_templates",

src/sbin/lorax

@@ -24,6 +24,9 @@ log = logging.getLogger("lorax")
 dnf_log = logging.getLogger("dnf")
 
 
+import atexit
+import fcntl
+from glob import glob
 import sys
 import os
 import tempfile
@@ -37,6 +40,42 @@ from pylorax import DRACUT_DEFAULT, DEFAULT_PLATFORM_ID, log_selinux_state
 from pylorax.cmdline import lorax_parser
 from pylorax.sysutils import flatconfig
 
+def exit_handler(tempdir):
+    """Handle cleanup of tmpdir, if it still exists
+    """
+    if not tempdir:
+        return
+    if os.path.exists(tempdir):
+        log.info("Cleaning up tempdir - %s", tempdir)
+        shutil.rmtree(tempdir)
+
+
+def remove_tempdirs():
+    """Delete all unlocked tempdirs under tempfile.gettempdir
+
+    When lorax crashes it can leave behind tempdirs, which cannot be cleaned up by
+    systemd-tmpfiles (SELinux restricts a complete cleanup).
+
+    So we lock them while in use and cleanup all the ones that are not locked
+    when lorax starts.
+    """
+    for d in glob(os.path.join(tempfile.gettempdir(), "lorax.*")):
+        if not os.path.isdir(d):
+            continue
+        try:
+            dir_fd = os.open(d, os.O_RDONLY|os.O_DIRECTORY|os.O_CLOEXEC)
+            fcntl.flock(dir_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        except OSError:
+            # lock failed, skip this directory
+            os.close(dir_fd)
+            continue
+
+        # Lock succeeded, remove the directory
+        log.info("Removing old tempdir %s", d)
+        shutil.rmtree(d)
+        os.close(dir_fd)
+
+
 def setup_logging(opts):
     pylorax.setup_logging(opts.logfile, log)
 
@@ -76,15 +115,28 @@ def main():
     log_selinux_state()
 
     if not opts.workdir:
+        if not os.path.exists(opts.tmp):
+            os.makedirs(opts.tmp)
+
         tempfile.tempdir = opts.tmp
 
+        # Remove any orphaned lorax tempdirs
+        remove_tempdirs()
+
         # create the temporary directory for lorax
-        tempdir = tempfile.mkdtemp(prefix="lorax.", dir=tempfile.gettempdir())
+        tempdir = tempfile.mkdtemp(prefix="lorax.")
+
+        # register an exit handler to cleanup the temporary directory
+        atexit.register(exit_handler, tempdir)
     else:
+        # NOTE: workdir is not cleaned up on exit
         tempdir = opts.workdir
         if not os.path.exists(tempdir):
             os.makedirs(tempdir)
 
+        # Remove any orphaned lorax tempdirs
+        remove_tempdirs()
+
     installtree = os.path.join(tempdir, "installtree")
     if not os.path.exists(installtree):
         os.mkdir(installtree)
@@ -92,15 +144,18 @@ def main():
     if not os.path.exists(dnftempdir):
         os.mkdir(dnftempdir)
 
+    # Obtain an exclusive lock on the tempdir
+    dir_fd = os.open(tempdir, os.O_RDONLY|os.O_DIRECTORY|os.O_CLOEXEC)
+    fcntl.flock(dir_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+
     dnfbase = get_dnf_base_object(installtree, opts.source, opts.mirrorlist, opts.repos,
                                   opts.enablerepos, opts.disablerepos,
                                   dnftempdir, opts.proxy, opts.version, opts.cachedir,
                                   os.path.dirname(opts.logfile), not opts.noverifyssl)
 
     if dnfbase is None:
+        os.close(dir_fd)
         print("error: unable to create the dnf base object", file=sys.stderr)
-        if not opts.workdir:
-            shutil.rmtree(tempdir)
         sys.exit(1)
 
     parsed_add_template_vars = {}
@@ -139,6 +194,8 @@ def main():
               remove_temp=True, verify=opts.verify,
               user_dracut_args=opts.dracut_args)
 
+    # Release the lock on the tempdir
+    os.close(dir_fd)
 
 def get_dnf_base_object(installroot, sources, mirrorlists=None, repos=None,
                         enablerepos=None, disablerepos=None,

systemd/lorax.conf

@@ -0,0 +1,3 @@
+# Prevent systemd from removing installtree files
+# This should eventually be fixed by - https://github.com/systemd/systemd/pull/11482
+x /var/tmp/lorax 750 root root