fix(proxy): close by-id authorization bypass on /v1/model/info

The `litellm_model_id` query branch in `model_info_v1` returned
deployment metadata before the listing-path user-filter ever ran,
so a user restricted by `LiteLLM_UserTable.models` could pull info
for any deployment via `/v1/model/info?litellm_model_id=<id>`.

Reported by @veria-ai on this PR. Fix in-place rather than as a
follow-up since closing the discovery-vs-inference gap is the PR's
whole point.

- After `llm_router.get_deployment(...)` resolves, call
  `get_available_models_for_user` (same signature as the listing
  path) and intersect against `deployment_info.model_name`.
- If not in the authorized list, raise `HTTPException(403, ...)`
  with a "not authorized" message — 403, not 404, since the user
  IS authenticated, matching inference-time `can_user_call_model`.
- Admin / master-key unaffected: `_apply_user_models_filter`
  returns `all_models` unchanged when `user_api_key_dict.user_id`
  is None.

Tests (`test_v1_model_info_user_filter.py`):
- `test_v1_model_info_by_id_denied_when_model_not_in_user_models`
- `test_v1_model_info_by_id_allowed_when_model_in_user_models`
- `test_v1_model_info_by_id_master_key_bypass`

11/11 pass locally.

litellm/proxy/proxy_server.py

@@ -13445,6 +13445,30 @@ async def model_info_v1(
                     "error": f"Model id = {litellm_model_id} not found on litellm proxy"
                 },
             )
+        # Authorize against user.models — by-id was previously
+        # short-circuiting before the listing-path filter.
+        from litellm.proxy.utils import get_available_models_for_user
+
+        authorized_models = await get_available_models_for_user(
+            user_api_key_dict=user_api_key_dict,
+            llm_router=llm_router,
+            general_settings=general_settings,
+            user_model=user_model,
+            prisma_client=prisma_client,
+            proxy_logging_obj=proxy_logging_obj,
+            team_id=None,
+            include_model_access_groups=False,
+            only_model_access_groups=False,
+            return_wildcard_routes=False,
+            user_api_key_cache=user_api_key_cache,
+        )
+        if deployment_info.model_name not in authorized_models:
+            raise HTTPException(
+                status_code=403,
+                detail={
+                    "error": f"Model id = {litellm_model_id} not authorized for this user"
+                },
+            )
         _deployment_info_dict = _get_proxy_model_info(
             model=deployment_info.model_dump(exclude_none=True)
         )

tests/test_litellm/proxy/discovery_endpoints/test_v1_model_info_user_filter.py

@@ -236,3 +236,69 @@ def test_v1_model_info_alias_route_filters_identically(
     resp = client.get("/model/info", headers={"Authorization": "Bearer sk-test"})
     assert resp.status_code == 200
     assert _model_names(resp.json()) == ["claude-3-opus"]
+
+
+# ---------------------------------------------------------------------------
+# /v1/model/info Path A (?litellm_model_id=...) — by-id authorization
+# ---------------------------------------------------------------------------
+
+
+def _deployment_id(router, model_name):
+    for d in router.model_list:
+        if d["model_name"] == model_name:
+            return d["model_info"]["id"]
+    raise AssertionError(f"model {model_name!r} not in router")
+
+
+def test_v1_model_info_by_id_denied_when_model_not_in_user_models(
+    client, configure_router, monkeypatch
+):
+    """Regression: by-id lookup must respect user.models (veria-ai #29748)."""
+    _override_auth(user_id="u-test")
+    _patch_user(monkeypatch, models=["gpt-4"])
+    disallowed_id = _deployment_id(configure_router, "claude-3-opus")
+
+    resp = client.get(
+        f"/v1/model/info?litellm_model_id={disallowed_id}",
+        headers={"Authorization": "Bearer sk-test"},
+    )
+    assert resp.status_code == 403
+    assert "not authorized" in resp.text.lower()
+
+
+def test_v1_model_info_by_id_allowed_when_model_in_user_models(
+    client, configure_router, monkeypatch
+):
+    """By-id lookup for a deployment whose model_name is in user.models -> 200."""
+    _override_auth(user_id="u-test")
+    _patch_user(monkeypatch, models=["claude-3-opus"])
+    allowed_id = _deployment_id(configure_router, "claude-3-opus")
+
+    resp = client.get(
+        f"/v1/model/info?litellm_model_id={allowed_id}",
+        headers={"Authorization": "Bearer sk-test"},
+    )
+    assert resp.status_code == 200
+    assert _model_names(resp.json()) == ["claude-3-opus"]
+
+
+def test_v1_model_info_by_id_master_key_bypass(client, configure_router, monkeypatch):
+    """Master key / service account (user_id=None) -> by-id lookup unrestricted."""
+
+    async def _should_not_be_called(*args, **kwargs):
+        raise AssertionError("get_user_object must not be called when user_id is None")
+
+    monkeypatch.setattr(
+        "litellm.proxy.auth.auth_checks.get_user_object",
+        _should_not_be_called,
+    )
+
+    _override_auth(user_id=None)
+    any_id = _deployment_id(configure_router, "claude-3-opus")
+
+    resp = client.get(
+        f"/v1/model/info?litellm_model_id={any_id}",
+        headers={"Authorization": "Bearer sk-test"},
+    )
+    assert resp.status_code == 200
+    assert _model_names(resp.json()) == ["claude-3-opus"]