### Related issues
Closes#14648
### What problem does this PR solve?
This PR fixes an authorization flaw in `POST /files/link-to-datasets`.
Before this change, the endpoint only checked whether the supplied
`file_ids` and `kb_ids` existed. It did not verify whether the
authenticated user was actually allowed to access those files or target
datasets. As a result, an authenticated user who knew valid IDs could
relink another user's files to arbitrary datasets.
This was especially risky because the relinking flow is state-changing:
the background worker removes existing file-document mappings and then
recreates documents under the attacker-supplied dataset IDs.
This change makes the route enforce the same permission model already
used by nearby file and document operations:
- each resolved file must pass `check_file_team_permission(...)`
- each target dataset must pass `check_kb_team_permission(...)`
- authorization is enforced before scheduling background relinking work
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):
### Testing
- Added regression coverage in
`test/testcases/test_web_api/test_file_app/test_file2document_routes_unit.py`
- Covered:
- unauthorized file access is rejected
- unauthorized dataset access is rejected
- existing success path still returns immediately after scheduling
background work
- Attempted to run:
- `python -m pytest
test\\testcases\\test_web_api\\test_file_app\\test_file2document_routes_unit.py
-q`
- Local execution in this workspace is currently blocked by missing test
dependencies during bootstrap, including `ragflow_sdk`
---------
Co-authored-by: jony376 <jony376@gmail.com>
