Contain remote log upload paths within base_log_folder

[potiuk]

Why

S3RemoteLogIO.upload, GCSRemoteLogIO.upload and WasbRemoteLogIO.upload build the local log path as base_log_folder.joinpath(path), then read that file and — when delete_local_copy is set — shutil.rmtree(os.path.dirname(local_loc)).

joinpath and PurePath.relative_to are purely lexical: neither normalises ... A relative log path containing .. therefore resolves outside base_log_folder, so its contents get uploaded to the remote log store and its parent directory gets removed.

CloudWatchRemoteLogIO.upload, in the same package, already guards exactly this operation:

base = self.base_log_folder.resolve()
local_path = (raw if raw.is_absolute() else base / raw).resolve()
try:
    local_path.relative_to(base)
except ValueError:
    self.log.warning("Skipping deletion: path %s is outside base_log_folder %s", local_path, base)
    return

So the correct behaviour is already established here — three of the four remote log handlers just don't have it. This makes them consistent.

What

• Add a resolve() + relative_to(base_log_folder) containment check to upload() in the S3, GCS and WASB remote log handlers, skipping with a warning when the path escapes — mirroring the CloudWatch handler.
• The check runs before the file is read, so it covers both the read/upload and the delete_local_copy deletion.
• Add a test to each of the three provider test suites covering the traversing path and asserting the file and its parent survive.

Compatibility

No behaviour change for paths that resolve inside base_log_folder. That explicitly includes relative paths with internal .. segments that stay within the folder (e.g. dag_id=a/../1.log), and absolute paths inside the folder — both verified.

Testing

moto and the other provider test dependencies aren't available in my local environment, so I could not execute the three provider suites — CI needs to run them. What I did verify locally:

• py_compile and ruff check clean on all six changed files.
• The containment arithmetic itself, exercised against real temporary directories across six cases: normal relative path (allowed), .. traversal (blocked), deep traversal (blocked), absolute inside base (allowed), absolute outside base (blocked), and internal .. staying inside (allowed — confirming no false positives on legitimate paths).

🤖 Generated with Claude Code

[potiuk]

Rebased onto current main and CI is green (66 checks, nothing failing).

The one review point — the comment above the containment check being too long — is addressed in baa3ac4abe: the prose restatement is gone, and what's left is the two lines that say why the check exists rather than what it does, applied to all three handlers.

Ready for another look whenever suits.

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Drafted-by: Claude Code (Opus 5); reviewed by @potiuk before posting