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WIP: Implement Linux User Namespaces support #248

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WIP: Implement Linux User Namespaces support #248

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64 changes: 54 additions & 10 deletions dangerzone/container.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import gzip
import json
import logging
import os
import pipes
Expand Down Expand Up @@ -49,6 +50,19 @@ def get_runtime() -> str:
return runtime


def podman_get_subids():
info = subprocess.run(
["podman", "info", "-f", "json"], check=True, stdout=subprocess.PIPE
)
info_dict = json.loads(info.stdout)
for id_type in ["uid", "gid"]:
mapping = info_dict["host"]["idMappings"][f"{id_type}map"]
count = 0
for m in mapping[1:]:
count += m["size"]
yield count


def install() -> bool:
"""
Make sure the podman container is installed. Linux only.
Expand Down Expand Up @@ -158,7 +172,9 @@ def exec_container(
if get_runtime_name() == "podman":
platform_args = []
security_args = ["--security-opt", "no-new-privileges"]
security_args += ["--userns", "keep-id"]
num_subuids, num_subgids = podman_get_subids()
security_args += ["--uidmap", f"0:1:{num_subuids}"]
security_args += ["--gidmap", f"0:1:{num_subgids}"]
else:
platform_args = ["--platform", "linux/amd64"]
security_args = ["--security-opt=no-new-privileges:true"]
Expand Down Expand Up @@ -189,6 +205,29 @@ def convert(
output_filename: str,
ocr_lang: Optional[str],
stdout_callback: Callable[[str], None],
) -> bool:
dz_tmp = os.path.join(appdirs.user_config_dir("dangerzone"), "tmp")
os.makedirs(dz_tmp, exist_ok=True)
tmpdir = tempfile.TemporaryDirectory(dir=dz_tmp)

try:
return _convert(tmpdir, input_filename, output_filename, ocr_lang,
stdout_callback)
finally:
if get_runtime_name() == "podman":
subprocess.run([
"podman", "unshare", "chown", "-R", "0:0", tmpdir.name
], check=True)
# Clean up
tmpdir.cleanup()


def _convert(
tmpdir: tempfile.TemporaryDirectory,
input_filename: str,
output_filename: str,
ocr_lang: Optional[str],
stdout_callback: Callable[[str], None],
) -> bool:
success = False

Expand All @@ -197,20 +236,23 @@ def convert(
else:
ocr = "0"

dz_tmp = os.path.join(appdirs.user_config_dir("dangerzone"), "tmp")
os.makedirs(dz_tmp, exist_ok=True)

tmpdir = tempfile.TemporaryDirectory(dir=dz_tmp)
tmp_input_file = os.path.join(tmpdir.name, "input_file")
pixel_dir = os.path.join(tmpdir.name, "pixels")
safe_dir = os.path.join(tmpdir.name, "safe")
shutil.copy(input_filename, tmp_input_file)
os.makedirs(pixel_dir, exist_ok=True)
os.makedirs(safe_dir, exist_ok=True)

if get_runtime_name() == "podman":
subprocess.run([
"podman", "unshare", "chown", "-R", "1001:1001", tmpdir.name
], check=True)

# Convert document to pixels
command = ["/usr/bin/python3", "/usr/local/bin/dangerzone.py", "document-to-pixels"]
Comment on lines 244 to 252
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What do you think about grouping together the "unshares" with a context manager? The core code would look a bit more organized:

    [...]
    with namespaced_tmpdir(tmpdir):
        # Convert document to pixels
        command = ["/usr/bin/python3", "/usr/local/bin/dangerzone.py", "document-to-pixels"]
        ...

The context manager I'm using looks like:

from contextlib import contextmanager

@contextmanager
def namespaced_tmpdir(tmpdir: tempfile.TemporaryDirectory):
    """Some more detailed explanation"""
    try:
        if get_runtime_name() == "podman":
            unshare_cmd = ["podman", "unshare", "chown", "-R", "1001:1001", tmpdir.name]
            log.debug("> " + " ".join(unshare_cmd))
            subprocess.run(unshare_cmd, check=True)
        yield
    finally:
        if get_runtime_name() == "podman":
            unshare_cmd = ["podman", "unshare", "chown", "-R", "0:0", tmpdir.name]
            log.debug("> " + " ".join(unshare_cmd))
            subprocess.run(unshare_cmd, check=True)

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I have implemented an example of this here 3de0633.

extra_args = [
"-v",
f"{input_filename}:/tmp/input_file",
f"{tmp_input_file}:/tmp/input_file",
"-v",
f"{pixel_dir}:/dangerzone",
]
Expand Down Expand Up @@ -243,14 +285,16 @@ def convert(
container_output_filename = os.path.join(
safe_dir, "safe-output-compressed.pdf"
)
shutil.move(container_output_filename, output_filename)

if get_runtime_name() == "podman":
subprocess.run([
"podman", "unshare", "chown", "-R", "0:0", tmpdir.name
], check=True)
shutil.move(container_output_filename, output_filename)

# We did it
success = True

# Clean up
tmpdir.cleanup()

return success


Expand Down