anti
99ccd41bb5
Harden the attacker-controlled artifact download path (F7) with explicit response headers instead of relying on Starlette's defaults (which only emit attachment for non-ASCII filenames and never set nosniff). Also resolves the THREAT_MODEL F7 path-traversal row (containment check was already in _resolve_artifact_path) and the fleet-deploy detail=str(e) audit (all four sites are admin-gated deliberate validator UX or structured worker-response fields).
96 lines
3.6 KiB
Python
96 lines
3.6 KiB
Python
"""
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Artifact download endpoint.
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SSH deckies farm attacker file drops into a host-mounted quarantine:
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/var/lib/decnet/artifacts/{decky}/ssh/{stored_as}
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The capture event already flows through the normal log pipeline (one
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RFC 5424 line per capture, see templates/ssh/emit_capture.py), so metadata
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is served via /logs. This endpoint exists only to retrieve the raw bytes —
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admin-gated because the payloads are attacker-controlled content.
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"""
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from __future__ import annotations
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import os
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import re
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from pathlib import Path
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from fastapi import APIRouter, Depends, HTTPException, Query
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from fastapi.responses import FileResponse
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from decnet.telemetry import traced as _traced
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from decnet.web.dependencies import require_admin
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router = APIRouter()
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# Override via env for tests; the prod path matches the bind mount declared in
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# decnet/services/ssh.py and decnet/services/smtp.py.
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ARTIFACTS_ROOT = Path(os.environ.get("DECNET_ARTIFACTS_ROOT", "/var/lib/decnet/artifacts"))
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# decky names come from the deployer — lowercase alnum plus hyphens.
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_DECKY_RE = re.compile(r"^[a-z0-9][a-z0-9-]{0,62}$")
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# Services that own an artifacts subdir. Kept explicit so a caller can't
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# pivot into arbitrary subpaths via the query string.
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_ALLOWED_SERVICES = {"ssh", "smtp"}
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# stored_as is assembled by the capturing template as:
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# ${ts}_${sha:0:12}_${base}
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# where ts is ISO-8601 UTC (e.g. 2026-04-18T02:22:56Z), sha is 12 hex chars,
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# and base is the original filename's basename. Keep the filename charset
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# tight but allow common punctuation dropped files actually use.
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_STORED_AS_RE = re.compile(
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r"^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z_[a-f0-9]{12}_[A-Za-z0-9._-]{1,255}$"
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)
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def _resolve_artifact_path(decky: str, stored_as: str, service: str) -> Path:
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"""Validate inputs, resolve the on-disk path, and confirm it stays inside
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the artifacts root. Raises HTTPException(400) on any violation."""
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if service not in _ALLOWED_SERVICES:
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raise HTTPException(status_code=400, detail="invalid service")
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if not _DECKY_RE.fullmatch(decky):
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raise HTTPException(status_code=400, detail="invalid decky name")
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if not _STORED_AS_RE.fullmatch(stored_as):
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raise HTTPException(status_code=400, detail="invalid stored_as")
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root = ARTIFACTS_ROOT.resolve()
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candidate = (root / decky / service / stored_as).resolve()
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# defence-in-depth: even though the regexes reject `..`, make sure a
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# symlink or weird filesystem state can't escape the root.
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if root not in candidate.parents and candidate != root:
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raise HTTPException(status_code=400, detail="path escapes artifacts root")
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return candidate
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@router.get(
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"/artifacts/{decky}/{stored_as}",
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tags=["Artifacts"],
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responses={
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400: {"description": "Invalid decky, service, or stored_as parameter"},
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401: {"description": "Could not validate credentials"},
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403: {"description": "Admin access required"},
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404: {"description": "Artifact not found"},
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},
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)
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@_traced("api.get_artifact")
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async def get_artifact(
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decky: str,
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stored_as: str,
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service: str = Query("ssh", pattern=r"^[a-z]{1,16}$"),
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admin: dict = Depends(require_admin),
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) -> FileResponse:
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path = _resolve_artifact_path(decky, stored_as, service)
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if not path.is_file():
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raise HTTPException(status_code=404, detail="artifact not found")
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return FileResponse(
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path=str(path),
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media_type="application/octet-stream",
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filename=stored_as,
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headers={
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"Content-Disposition": f'attachment; filename="{stored_as}"',
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"X-Content-Type-Options": "nosniff",
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},
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)
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