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https://github.com/freedomofpress/dangerzone.git
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df1ec758bc
Mask some paths of the outer container in the OCI config of the inner container. This is done to avoid leaking any sensitive information from Podman / Docker / gVisor, since we reuse the same rootfs Refs #1048
250 lines
8.1 KiB
Python
Executable file
250 lines
8.1 KiB
Python
Executable file
#!/usr/bin/python3
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import json
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import os
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import shlex
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import subprocess
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import sys
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import typing
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# This script wraps the command-line arguments passed to it to run as an
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# unprivileged user in a gVisor sandbox.
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# Its behavior can be modified with the following environment variables:
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# RUNSC_DEBUG: If set, print debug messages to stderr, and log all gVisor
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# output to stderr.
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# RUNSC_FLAGS: If set, pass these flags to the `runsc` invocation.
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# These environment variables are not passed on to the sandboxed process.
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def log(message: str, *values: typing.Any) -> None:
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"""Helper function to log messages if RUNSC_DEBUG is set."""
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if os.environ.get("RUNSC_DEBUG"):
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print(message.format(*values), file=sys.stderr)
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command = sys.argv[1:]
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if len(command) == 0:
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log("Invoked without a command; will execute 'sh'.")
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command = ["sh"]
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else:
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log("Invoked with command: {}", " ".join(shlex.quote(s) for s in command))
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# Build and write container OCI config.
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oci_config: dict[str, typing.Any] = {
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"ociVersion": "1.0.0",
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"process": {
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"user": {
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# Hardcode the UID/GID of the container image to 1000, since we're in
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# control of the image creation, and we don't expect it to change.
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"uid": 1000,
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"gid": 1000,
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},
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"args": command,
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"env": [
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"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
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"PYTHONPATH=/opt/dangerzone",
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"TERM=xterm",
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],
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"cwd": "/",
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"capabilities": {
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"bounding": [],
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"effective": [],
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"inheritable": [],
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"permitted": [],
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},
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"rlimits": [
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{"type": "RLIMIT_NOFILE", "hard": 4096, "soft": 4096},
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],
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},
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"root": {"path": "/", "readonly": True},
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"hostname": "dangerzone",
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"mounts": [
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# Mask almost every system directory of the outer container, by mounting tmpfs
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# on top of them. This is done to avoid leaking any sensitive information,
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# either mounted by Podman/Docker, or when gVisor runs, since we reuse the same
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# rootfs. We basically mask everything except for `/usr`, `/bin`, `/lib`,
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# and `/etc`.
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#
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# Note that we set `--root /home/dangerzone/.containers` for the directory where
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# gVisor will create files at runtime, which means that in principle, we are
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# covered by the masking of `/home/dangerzone` that follows below.
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#
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# Finally, note that the following list has been taken from the dirs in our
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# container image, and double-checked against the top-level dirs listed in the
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# Filesystem Hierarchy Standard (FHS) [1]. It would be nice to have an allowlist
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# approach instead of a denylist, but FHS is such an old standard that we don't
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# expect any new top-level dirs to pop up any time soon.
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#
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# [1] https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
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{
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"destination": "/boot",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/dev",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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{
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"destination": "/home",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/media",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/mnt",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/proc",
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"type": "proc",
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"source": "proc",
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},
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{
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"destination": "/root",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/run",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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{
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"destination": "/sbin",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/srv",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/sys",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev", "ro"],
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},
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{
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"destination": "/tmp",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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{
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"destination": "/var",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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# Also mask some files that are usually mounted by Docker / Podman. These files
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# should not contain any sensitive information, since we use the `--network
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# none` flag, but we want to make sure in any case.
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{
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"destination": "/etc/hostname",
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"type": "bind",
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"source": "/dev/null",
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"options": ["rbind", "ro"],
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},
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{
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"destination": "/etc/hosts",
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"type": "bind",
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"source": "/dev/null",
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"options": ["rbind", "ro"],
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},
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# LibreOffice needs a writable home directory, so just mount a tmpfs
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# over it.
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{
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"destination": "/home/dangerzone",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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# Used for LibreOffice extensions, which are only conditionally
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# installed depending on which file is being converted.
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{
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"destination": "/usr/lib/libreoffice/share/extensions/",
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"type": "tmpfs",
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"source": "tmpfs",
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"options": ["nosuid", "noexec", "nodev"],
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},
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],
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"linux": {
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"namespaces": [
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{"type": "pid"},
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{"type": "network"},
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{"type": "ipc"},
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{"type": "uts"},
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{"type": "mount"},
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],
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},
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}
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not_forwarded_env = set(
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(
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"PATH",
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"HOME",
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"SHLVL",
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"HOSTNAME",
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"TERM",
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"PWD",
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"RUNSC_FLAGS",
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"RUNSC_DEBUG",
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)
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)
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for key_val in oci_config["process"]["env"]:
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not_forwarded_env.add(key_val[: key_val.index("=")])
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for key, val in os.environ.items():
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if key in not_forwarded_env:
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continue
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oci_config["process"]["env"].append("%s=%s" % (key, val))
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if os.environ.get("RUNSC_DEBUG"):
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log("Command inside gVisor sandbox: {}", command)
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log("OCI config:")
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json.dump(oci_config, sys.stderr, indent=2, sort_keys=True)
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# json.dump doesn't print a trailing newline, so print one here:
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log("")
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with open("/config.json", "w") as oci_config_out:
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json.dump(oci_config, oci_config_out, indent=2, sort_keys=True)
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# Run gVisor.
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runsc_argv = [
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"/usr/bin/runsc",
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"--rootless=true",
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"--network=none",
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"--root=/home/dangerzone/.containers",
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# Disable DirectFS for to make the seccomp filter even stricter,
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# at some performance cost.
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"--directfs=false",
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]
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if os.environ.get("RUNSC_DEBUG"):
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runsc_argv += ["--debug=true", "--alsologtostderr=true"]
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if os.environ.get("RUNSC_FLAGS"):
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runsc_argv += [x for x in shlex.split(os.environ.get("RUNSC_FLAGS", "")) if x]
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runsc_argv += ["run", "--bundle=/", "dangerzone"]
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log(
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"Running gVisor with command line: {}", " ".join(shlex.quote(s) for s in runsc_argv)
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)
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runsc_process = subprocess.run(
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runsc_argv,
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check=False,
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)
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log("gVisor quit with exit code: {}", runsc_process.returncode)
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# We're done.
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sys.exit(runsc_process.returncode)
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