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fix(guard): reject data-modifying CTEs in SqlGuard - #49
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A statement like `WITH x AS (UPDATE foo ...) SELECT ...` parses as a Select and passed every gate, because the resolver never populates its update/insert column lists for DML wrapped in a WITH item. The guard then returned the write statement as approved SQL. Add ReadOnlyStatementValidator, which walks the parsed Select tree (reusing TablesNamesFinder's recursion) and rejects any WITH item that wraps an UPDATE/INSERT/DELETE instead of a SELECT. Run it before resolve(), which also stops the INSERT-in-CTE ClassCastException leak. Signed-off-by: Stefan Bischof <stbischof@bipolis.org>
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A statement like
WITH x AS (UPDATE foo ...) SELECT ...parses as a Select and passed every gate, because the resolver never populates its update/insert column lists for DML wrapped in a WITH item. The guard then returned the write statement as approved SQL.Add ReadOnlyStatementValidator, which walks the parsed Select tree (reusing TablesNamesFinder's recursion) and rejects any WITH item that wraps an UPDATE/INSERT/DELETE instead of a SELECT. Run it before resolve(), which also stops the INSERT-in-CTE ClassCastException leak.