Do not follow symlinks for compressed file variants (#8652)

Co-authored-by: Steve Repsher <steverep@users.noreply.github.com>

CHANGES/8652.bugfix.rst

@@ -0,0 +1 @@
+Fixed incorrectly following symlinks for compressed file variants -- by :user:`steverep`.

aiohttp/web_fileresponse.py

@@ -174,7 +174,10 @@ def _get_file_path_stat_encoding(
 
             compressed_path = file_path.with_suffix(file_path.suffix + file_extension)
             with suppress(OSError):
-                return compressed_path, compressed_path.stat(), file_encoding
+                # Do not follow symlinks and ignore any non-regular files.
+                st = compressed_path.lstat()
+                if S_ISREG(st.st_mode):
+                    return compressed_path, st, file_encoding
 
         # Fallback to the uncompressed file
         return file_path, file_path.stat(), None

tests/test_web_sendfile.py

@@ -19,9 +19,9 @@ def test_using_gzip_if_header_present_and_file_available(loop: Any) -> None:
     )
 
     gz_filepath = mock.create_autospec(Path, spec_set=True)
-    gz_filepath.stat.return_value.st_size = 1024
-    gz_filepath.stat.return_value.st_mtime_ns = 1603733507222449291
-    gz_filepath.stat.return_value.st_mode = MOCK_MODE
+    gz_filepath.lstat.return_value.st_size = 1024
+    gz_filepath.lstat.return_value.st_mtime_ns = 1603733507222449291
+    gz_filepath.lstat.return_value.st_mode = MOCK_MODE
 
     filepath = mock.create_autospec(Path, spec_set=True)
     filepath.name = "logo.png"
@@ -41,9 +41,9 @@ def test_gzip_if_header_not_present_and_file_available(loop: Any) -> None:
     request = make_mocked_request("GET", "http://python.org/logo.png", headers={})
 
     gz_filepath = mock.create_autospec(Path, spec_set=True)
-    gz_filepath.stat.return_value.st_size = 1024
-    gz_filepath.stat.return_value.st_mtime_ns = 1603733507222449291
-    gz_filepath.stat.return_value.st_mode = MOCK_MODE
+    gz_filepath.lstat.return_value.st_size = 1024
+    gz_filepath.lstat.return_value.st_mtime_ns = 1603733507222449291
+    gz_filepath.lstat.return_value.st_mode = MOCK_MODE
 
     filepath = mock.create_autospec(Path, spec_set=True)
     filepath.name = "logo.png"
@@ -91,7 +91,7 @@ def test_gzip_if_header_present_and_file_not_available(loop: Any) -> None:
     )
 
     gz_filepath = mock.create_autospec(Path, spec_set=True)
-    gz_filepath.stat.side_effect = OSError(2, "No such file or directory")
+    gz_filepath.lstat.side_effect = OSError(2, "No such file or directory")
 
     filepath = mock.create_autospec(Path, spec_set=True)
     filepath.name = "logo.png"

tests/test_web_urldispatcher.py

@@ -514,6 +514,38 @@ async def test_access_symlink_loop(
     assert r.status == 404
 
 
+async def test_access_compressed_file_as_symlink(
+    tmp_path: pathlib.Path, aiohttp_client: AiohttpClient
+) -> None:
+    """Test that compressed file variants as symlinks are ignored."""
+    private_file = tmp_path / "private.txt"
+    private_file.write_text("private info")
+    www_dir = tmp_path / "www"
+    www_dir.mkdir()
+    gz_link = www_dir / "file.txt.gz"
+    gz_link.symlink_to(f"../{private_file.name}")
+
+    app = web.Application()
+    app.router.add_static("/", www_dir)
+    client = await aiohttp_client(app)
+
+    # Symlink should be ignored; response reflects missing uncompressed file.
+    resp = await client.get(f"/{gz_link.stem}", auto_decompress=False)
+    assert resp.status == 404
+    resp.release()
+
+    # Again symlin is ignored, and then uncompressed is served.
+    txt_file = gz_link.with_suffix("")
+    txt_file.write_text("public data")
+    resp = await client.get(f"/{txt_file.name}")
+    assert resp.status == 200
+    assert resp.headers.get("Content-Encoding") is None
+    assert resp.content_type == "text/plain"
+    assert await resp.text() == "public data"
+    resp.release()
+    await client.close()
+
+
 async def test_access_special_resource(
     tmp_path_factory: pytest.TempPathFactory, aiohttp_client: AiohttpClient
 ) -> None: