{confcom}: Simplify logic in map_image_from_tar(_compatibility)?

[micromaomao]

The current code extracts an item in the tar based on a path controlled by the
manifest within the tar, which is prone to path traversal on Linux and Windows,
and potentially other path confusion attacks on Windows if the Config field in
the manifest contains special names.

This extraction is unnecessary as we can read the content of the config directly
from the tar file using extractfile. This commit simplifies it to do that.

Also, there are two versions of the map_image_from_tar function, with the second
one introduced in #7414. Later code changes in #8238 means that these functions
now do basically the same thing (with different clean up code). After this
simplification, these two functions are exactly the same, so let's also remove
the _compatibility one.

Before:

> az confcom acipolicygen --image mcr.microsoft.com/aci/skr:2.14 --tar image-docker-malformed.tar --outraw-pretty-print
...
Pulling and hashing images...:   0%|                                                                                                        | 0/2 [00:00<?, ?percent/s]
ERROR: The command failed with an unexpected error. Here is the traceback:
ERROR: [Errno 13] Permission denied: '../../../../../blobs'
Traceback (most recent call last):
File "/home/mao/.az-cli-newpy.venv/lib/python3.13/site-packages/knack/cli.py", line 233, in invoke
    cmd_result = self.invocation.execute(args)
File "/home/mao/src/github.com/Microsoft/azure-cli/src/azure-cli-core/azure/cli/core/commands/__init__.py", line 677, in execute
    raise ex
File "/home/mao/src/github.com/Microsoft/azure-cli/src/azure-cli-core/azure/cli/core/commands/__init__.py", line 820, in _run_jobs_serially
    results.append(self._run_job(expanded_arg, cmd_copy))
                ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/mao/src/github.com/Microsoft/azure-cli/src/azure-cli-core/azure/cli/core/commands/__init__.py", line 789, in _run_job
    result = cmd_copy(params)
File "/home/mao/src/github.com/Microsoft/azure-cli/src/azure-cli-core/azure/cli/core/commands/__init__.py", line 335, in __call__
    return self.handler(*args, **kwargs)
        ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
File "/home/mao/src/github.com/Microsoft/azure-cli/src/azure-cli-core/azure/cli/core/commands/command_operation.py", line 120, in handler
    return op(**command_args)
File "/home/mao/.azure/cliextensions/confcom/azext_confcom/custom.py", line 197, in acipolicygen_confcom
    policy.populate_policy_content_for_all_images(
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        individual_image=bool(image_name), tar_mapping=tar_mapping, faster_hashing=faster_hashing
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
File "/home/mao/.azure/cliextensions/confcom/azext_confcom/security_policy.py", line 485, in populate_policy_content_for_all_images
    image_info, tar = get_image_info(progress, message_queue, tar_mapping, image)
                    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/mao/.azure/cliextensions/confcom/azext_confcom/template_util.py", line 111, in get_image_info
    image_info = os_util.map_image_from_tar_backwards_compatibility(
        image_name, tar_file, tar_location
    )
File "/home/mao/.azure/cliextensions/confcom/azext_confcom/os_util.py", line 190, in map_image_from_tar_backwards_compatibility
    tar.extract(info_file.name, path=tar_dir)
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/mao/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/tarfile.py", line 2416, in extract
    self._extract_one(tarinfo, path, set_attrs, numeric_owner)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/mao/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/tarfile.py", line 2464, in _extract_one
    self._handle_fatal_error(e)
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^
File "/home/mao/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/tarfile.py", line 2458, in _extract_one
    self._extract_member(tarinfo, os.path.join(path, tarinfo.name),
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        set_attrs=set_attrs,
                        ^^^^^^^^^^^^^^^^^^^^
                        numeric_owner=numeric_owner,
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        filter_function=filter_function,
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        extraction_root=path)
                        ^^^^^^^^^^^^^^^^^^^^^
File "/home/mao/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/tarfile.py", line 2539, in _extract_member
    os.makedirs(upperdirs, exist_ok=True)
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
File "<frozen os>", line 218, in makedirs
File "<frozen os>", line 228, in makedirs
PermissionError: [Errno 13] Permission denied: '../../../../../blobs'
To check existing issues, please visit: https://github.com/Azure/azure-cli/issues

After:

> az confcom acipolicygen --image mcr.microsoft.com/aci/skr:2.14 --tar image-docker-malformed.tar --outraw-pretty-print | grep -C10 layers
...
Pulling and hashing images...: 100%|████████████████████████████████████████████████████████████████████████████████████████████████| 2/2 [00:01<00:00,  1.38percent/s]
WARNING: mcr.microsoft.com/aci/skr:2.14 read from local tar file
        "strategy": "re2"
      },
      {
        "pattern": "azurecontainerinstance_restarted_by=.+",
        "required": false,
        "strategy": "re2"
      }
    ],
    "exec_processes": [],
    "id": "mcr.microsoft.com/aci/skr:2.14",
    "layers": [
      "a189b02d4858578459fda1dfbd7c6a4557c44208b9829e02b931771a6d611c39",
      "300f9661fb3d46c0f299ad6f552b7ad0c41ea5141755b0b3feaca3081a108f7a",
      "0afffca98bacf8e7b6e6f7982459a03219f60555523163c73c4b092e0a3deef2",
      "eefefd5009aed4ba4478876995d1a18aa3a670661fcc61d2e4cba6e2b79da0a1",
      "b868a7e1bebef40e5bf4d58fe271c0a10a351e68b12179ec019af9f6c75781ae",
      "8b4842f06982817534a75bcf71865213b09dfa8313229c384e5201dadbd75e25"
    ],
...

(Validated that this matches the result of using the image reference directly
without a tar, and also matches with the result of using the oci tar from oras backup)

Signed-off-by: Tingmao Wang tingmaowang@microsoft.com

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR mitigates path traversal risks when generating policies from Docker image tarballs by avoiding filesystem extraction and instead reading required JSON directly from the tar stream. It also removes redundant backwards-compatibility code now equivalent to the primary implementation.

Changes:

• Read manifest.json and the referenced config JSON directly from the tar via extractfile/read_file_from_tar (no extraction to disk).
• Remove map_image_from_tar_backwards_compatibility and its use in get_image_info.
• Bump extension version to 2.0.0b3 and document the security fix in HISTORY.rst.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
src/confcom/setup.py	Version bump to ship the fix (2.0.0b3).
src/confcom/azext_confcom/template_util.py	Removes backwards-compatibility tar parsing path.
src/confcom/azext_confcom/os_util.py	Eliminates disk extraction; reads manifest/config from tar stream; removes redundant function.
src/confcom/HISTORY.rst	Adds release note for the path traversal fix.

[Copilot]

tar.extractfile(...) can return None for non-regular members (e.g., directories/links). Calling .read() on None will raise AttributeError. Consider explicitly handling the None case and raising a clear exception (or KeyError) so the caller’s fallback logic behaves predictably.

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

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