merge: testing → main (reconcile 2-week divergence)

decnet/web/router/artifacts/api_get_artifact.py

@@ -0,0 +1,95 @@
+"""
+Artifact download endpoint.
+
+SSH deckies farm attacker file drops into a host-mounted quarantine:
+  /var/lib/decnet/artifacts/{decky}/ssh/{stored_as}
+
+The capture event already flows through the normal log pipeline (one
+RFC 5424 line per capture, see templates/ssh/emit_capture.py), so metadata
+is served via /logs. This endpoint exists only to retrieve the raw bytes —
+admin-gated because the payloads are attacker-controlled content.
+"""
+
+from __future__ import annotations
+
+import os
+import re
+from pathlib import Path
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi.responses import FileResponse
+
+from decnet.telemetry import traced as _traced
+from decnet.web.dependencies import require_admin
+
+router = APIRouter()
+
+# Override via env for tests; the prod path matches the bind mount declared in
+# decnet/services/ssh.py and decnet/services/smtp.py.
+ARTIFACTS_ROOT = Path(os.environ.get("DECNET_ARTIFACTS_ROOT", "/var/lib/decnet/artifacts"))
+
+# decky names come from the deployer — lowercase alnum plus hyphens.
+_DECKY_RE = re.compile(r"^[a-z0-9][a-z0-9-]{0,62}$")
+
+# Services that own an artifacts subdir. Kept explicit so a caller can't
+# pivot into arbitrary subpaths via the query string.
+_ALLOWED_SERVICES = {"ssh", "smtp"}
+
+# stored_as is assembled by the capturing template as:
+#   ${ts}_${sha:0:12}_${base}
+# where ts is ISO-8601 UTC (e.g. 2026-04-18T02:22:56Z), sha is 12 hex chars,
+# and base is the original filename's basename. Keep the filename charset
+# tight but allow common punctuation dropped files actually use.
+_STORED_AS_RE = re.compile(
+    r"^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z_[a-f0-9]{12}_[A-Za-z0-9._-]{1,255}$"
+)
+
+
+def _resolve_artifact_path(decky: str, stored_as: str, service: str) -> Path:
+    """Validate inputs, resolve the on-disk path, and confirm it stays inside
+    the artifacts root. Raises HTTPException(400) on any violation."""
+    if service not in _ALLOWED_SERVICES:
+        raise HTTPException(status_code=400, detail="invalid service")
+    if not _DECKY_RE.fullmatch(decky):
+        raise HTTPException(status_code=400, detail="invalid decky name")
+    if not _STORED_AS_RE.fullmatch(stored_as):
+        raise HTTPException(status_code=400, detail="invalid stored_as")
+
+    root = ARTIFACTS_ROOT.resolve()
+    candidate = (root / decky / service / stored_as).resolve()
+    # defence-in-depth: even though the regexes reject `..`, make sure a
+    # symlink or weird filesystem state can't escape the root.
+    if root not in candidate.parents and candidate != root:
+        raise HTTPException(status_code=400, detail="path escapes artifacts root")
+    return candidate
+
+
+@router.get(
+    "/artifacts/{decky}/{stored_as}",
+    tags=["Artifacts"],
+    responses={
+        400: {"description": "Invalid decky, service, or stored_as parameter"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Admin access required"},
+        404: {"description": "Artifact not found"},
+    },
+)
+@_traced("api.get_artifact")
+async def get_artifact(
+    decky: str,
+    stored_as: str,
+    service: str = Query("ssh", pattern=r"^[a-z]{1,16}$"),
+    admin: dict = Depends(require_admin),
+) -> FileResponse:
+    path = _resolve_artifact_path(decky, stored_as, service)
+    if not path.is_file():
+        raise HTTPException(status_code=404, detail="artifact not found")
+    return FileResponse(
+        path=str(path),
+        media_type="application/octet-stream",
+        filename=stored_as,
+        headers={
+            "Content-Disposition": f'attachment; filename="{stored_as}"',
+            "X-Content-Type-Options": "nosniff",
+        },
+    )