fix(gallery): confine replacement image path (#4285)

routes/gallery_routes.py

@@ -232,8 +232,6 @@ def setup_gallery_routes() -> APIRouter:
     @router.post("/api/gallery/{image_id}/replace")
     async def gallery_replace(request: Request, image_id: str):
         """Replace an existing gallery image file with a new one."""
-        from pathlib import Path
-
         user = get_current_user(request)
         db = SessionLocal()
         try:
@@ -249,9 +247,8 @@ def setup_gallery_routes() -> APIRouter:
                 raise HTTPException(400, "No image provided")
 
             content = await read_upload_limited(file, GALLERY_UPLOAD_MAX_BYTES, "Gallery replacement")
-            img_dir = Path(GENERATED_IMAGES_DIR)
-            img_dir.mkdir(parents=True, exist_ok=True)
-            img_path = img_dir / _sanitize_gallery_filename(img.filename)
+            GALLERY_IMAGE_DIR.mkdir(parents=True, exist_ok=True)
+            img_path = _gallery_image_path(img.filename)
             img_path.write_bytes(content)
 
             # Refresh dimensions in case the editor resized the canvas.

tests/test_gallery_filename_confinement.py

@@ -2,7 +2,14 @@ import os
 from pathlib import Path
 
 import pytest
+from fastapi import FastAPI
 from fastapi import HTTPException
+from fastapi.testclient import TestClient
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+from core.database import Base, GalleryImage
 
 
 def _gallery_module():
@@ -53,6 +60,57 @@ def test_gallery_image_path_rejects_symlink_escape(tmp_path, monkeypatch):
     assert exc.value.status_code == 400
 
 
+def test_gallery_replace_rejects_symlink_escape(tmp_path, monkeypatch):
+    gallery_routes = _gallery_module()
+    image_dir = tmp_path / "generated_images"
+    image_dir.mkdir()
+    outside = tmp_path / "outside.png"
+    outside.write_bytes(b"outside image root")
+    link = image_dir / "escape.png"
+    try:
+        os.symlink(outside, link)
+    except (AttributeError, NotImplementedError, OSError) as exc:
+        pytest.skip(f"symlinks unavailable: {exc}")
+
+    engine = create_engine(
+        f"sqlite:///{tmp_path / 'gallery.db'}",
+        connect_args={"check_same_thread": False},
+        poolclass=NullPool,
+    )
+    Base.metadata.create_all(engine)
+    SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+    db = SessionLocal()
+    try:
+        db.add(
+            GalleryImage(
+                id="img-1",
+                filename="escape.png",
+                prompt="escape",
+                owner="alice",
+                is_active=True,
+            )
+        )
+        db.commit()
+    finally:
+        db.close()
+
+    monkeypatch.setattr(gallery_routes, "GALLERY_IMAGE_DIR", image_dir)
+    monkeypatch.setattr(gallery_routes, "SessionLocal", SessionLocal)
+    monkeypatch.setattr(gallery_routes, "get_current_user", lambda request: "alice")
+
+    app = FastAPI()
+    app.include_router(gallery_routes.setup_gallery_routes())
+    client = TestClient(app)
+
+    response = client.post(
+        "/api/gallery/img-1/replace",
+        files={"image": ("replacement.png", b"replacement bytes", "image/png")},
+    )
+
+    assert response.status_code == 400
+    assert outside.read_bytes() == b"outside image root"
+
+
 def test_gallery_file_operations_use_confining_resolver():
     source = Path("routes/gallery_routes.py").read_text(encoding="utf-8")