d1b9304a56
This swaps the `systemd-nspawn` implementation for `bubblewrap` to
contain sub-processes. It also adjusts the `BuildRoot` implementation
to reduce the number of mounts required to keep locally.
This has the following advantages:
* We know exactly how the build-root looks like. Only the bits and
pieces we select will end up in the build-root. We can let RPM
authors know what environment their post-install scripts need to
run in, and we can reliably test this.
* We no longer need any D-Bus access or access to other PID1
facilities. Bubblewrap allows us to execute from any environment,
including containers and sandboxes.
* Bubblewrap setup is significantly faster than nspawn. This is a
minor point though, since nspawn is still fast enough compared to
the operations we perform in the container.
* Bubblewrap does not require root.
At the same time, we have a bunch of downsides which might increase the
workload in the future:
* We now control the build-root, which also means we have to make sure
it works on all our supported architectures, all quirks are
included, and all required resources are accessible from within the
build-root.
The good thing here is that we have lots of previous-art we can
follow, and all the other ones just play whack-a-mole, so we can
join that fun.
The `bubblewrap` project is used by podman and flatpak, it is packaged
for all major distributions, and looks like a stable dependency.
185 lines
6.9 KiB
Python
185 lines
6.9 KiB
Python
"""Build Roots
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This implements the file-system environment available to osbuild modules. It
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uses `bubblewrap` to contain osbuild modules in a private environment with as
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little access to the outside as possible.
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"""
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import contextlib
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import importlib
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import importlib.util
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import os
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import stat
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import subprocess
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import tempfile
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__all__ = [
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"BuildRoot",
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]
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# pylint: disable=too-many-instance-attributes
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class BuildRoot(contextlib.AbstractContextManager):
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"""Build Root
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This class implements a context-manager that maintains a root file-system
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for contained environments. When entering the context, the required
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file-system setup is performed, and it is automatically torn down when
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exiting.
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The `run()` method allows running applications in this environment. Some
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state is persistent across runs, including data in `/var`. It is deleted
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only when exiting the context manager.
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"""
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def __init__(self, root, runner, path="/run/osbuild", libdir=None, var="/var/tmp"):
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self._exitstack = None
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self._rootdir = root
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self._rundir = path
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self._vardir = var
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self._libdir = libdir
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self._runner = runner
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self.api = None
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self.dev = None
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self.var = None
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@staticmethod
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def _mknod(path, name, mode, major, minor):
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os.mknod(os.path.join(path, name),
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mode=(stat.S_IMODE(mode) | stat.S_IFCHR),
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device=os.makedev(major, minor))
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def __enter__(self):
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self._exitstack = contextlib.ExitStack()
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with self._exitstack:
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# We create almost everything directly in the container as temporary
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# directories and mounts. However, for some things we need external
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# setup. For these, we create temporary directories which are then
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# bind-mounted into the container.
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#
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# For now, this includes:
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#
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# * We create an API directory where the caller can place sockets
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# before we bind-mount it into the container on
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# `/run/osbuild/api`.
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#
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# * We create a tmpfs instance *without* `nodev` which we then use
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# as `/dev` in the container. This is required for the container
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# to create device nodes for loop-devices.
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#
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# * We create a temporary directory for variable data and then use
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# it as '/var' in the container. This allows the container to
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# create throw-away data that it does not want to put into a
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# tmpfs.
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api = tempfile.TemporaryDirectory(prefix="osbuild-api-", dir=self._rundir)
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self.api = self._exitstack.enter_context(api)
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dev = tempfile.TemporaryDirectory(prefix="osbuild-dev-", dir=self._rundir)
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self.dev = self._exitstack.enter_context(dev)
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var = tempfile.TemporaryDirectory(prefix="osbuild-var-", dir=self._vardir)
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self.var = self._exitstack.enter_context(var)
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subprocess.run(["mount", "-t", "tmpfs", "-o", "nosuid", "none", self.dev], check=True)
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self._exitstack.callback(lambda: subprocess.run(["umount", "--lazy", self.dev], check=True))
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self._mknod(self.dev, "full", 0o666, 1, 7)
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self._mknod(self.dev, "null", 0o666, 1, 3)
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self._mknod(self.dev, "random", 0o666, 1, 8)
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self._mknod(self.dev, "urandom", 0o666, 1, 9)
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self._mknod(self.dev, "tty", 0o666, 5, 0)
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self._mknod(self.dev, "zero", 0o666, 1, 5)
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self._exitstack = self._exitstack.pop_all()
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return self
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def __exit__(self, exc_type, exc_value, exc_tb):
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self._exitstack.close()
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self._exitstack = None
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def run(self, argv, binds=None, readonly_binds=None):
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"""Runs a command in the buildroot.
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Takes the command and arguments, as well as bind mounts to mirror
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in the build-root for this command.
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This must be called from within an active context of this buildroot
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context-manager.
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"""
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if not self._exitstack:
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raise RuntimeError("No active context")
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mounts = []
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# Import directories from the caller-provided root.
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for p in ["boot", "usr"]:
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source = os.path.join(self._rootdir, p)
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if os.path.isdir(source) and not os.path.islink(source):
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mounts += ["--ro-bind", source, os.path.join("/", p)]
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# Create /usr symlinks.
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mounts += ["--symlink", "usr/lib", "/lib"]
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mounts += ["--symlink", "usr/lib64", "/lib64"]
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mounts += ["--symlink", "usr/bin", "/bin"]
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mounts += ["--symlink", "usr/sbin", "/sbin"]
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# Setup /dev.
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mounts += ["--dev-bind", self.dev, "/dev"]
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mounts += ["--tmpfs", "/dev/shm"]
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# Setup temporary/data file-systems.
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mounts += ["--dir", "/etc"]
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mounts += ["--tmpfs", "/run"]
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mounts += ["--tmpfs", "/tmp"]
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mounts += ["--bind", self.var, "/var"]
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# Setup API file-systems.
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mounts += ["--proc", "/proc"]
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mounts += ["--bind", "/sys", "/sys"]
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# Make osbuild API-calls accessible to the container.
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mounts += ["--ro-bind", f"{self.api}", "/run/osbuild/api"]
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# We execute our own modules by bind-mounting them from the host into
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# the build-root. We have minimal requirements on the build-root, so
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# these modules can be executed. Everything else we provide ourselves.
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# In case you pass `--libdir`, it must be self-contained and we provide
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# nothing else. If you use the system libdir, we additionally look for
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# the installed `osbuild` module and bind-mount it as well.
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if self._libdir is not None:
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mounts += ["--ro-bind", f"{self._libdir}", "/run/osbuild/lib"]
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else:
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mounts += ["--ro-bind", "/usr/lib/osbuild", "/run/osbuild/lib"]
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modorigin = importlib.util.find_spec("osbuild").origin
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modpath = os.path.dirname(modorigin)
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mounts += ["--ro-bind", f"{modpath}", "/run/osbuild/lib/osbuild"]
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# Make caller-provided mounts available as well.
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for b in binds or []:
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mounts += ["--bind"] + b.split(":")
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for b in readonly_binds or []:
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mounts += ["--ro-bind"] + b.split(":")
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cmd = [
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"bwrap",
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"--cap-add", "CAP_MAC_ADMIN",
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"--chdir", "/",
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"--die-with-parent",
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"--new-session",
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"--setenv", "PATH", "/usr/sbin:/usr/bin",
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"--setenv", "PYTHONPATH", "/run/osbuild/lib",
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"--unshare-ipc",
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"--unshare-pid",
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]
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cmd += mounts
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cmd += ["--", f"/run/osbuild/lib/runners/{self._runner}"]
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cmd += argv
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return subprocess.run(cmd,
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check=False,
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stdin=subprocess.DEVNULL)
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