The `compaction_strategy_state` class holds strategy specific state via
a `std::variant` containing different state types. When a compaction
strategy performs compaction, it retrieves a reference to its state from
the `compaction_strategy_state` object. If the table's compaction
strategy is ALTERed while a compaction is in progress, the
`compaction_strategy_state` object gets replaced, destroying the old
state. This leaves the ongoing compaction holding a dangling reference,
resulting in a use after free.
Fix this by using `seastar::shared_ptr` for the state variant
alternatives(`leveled_compaction_strategy_state_ptr` and
`time_window_compaction_strategy_state_ptr`). The compaction strategies
now hold a copy of the shared_ptr, ensuring the state remains valid for
the duration of the compaction even if the strategy is altered.
The `compaction_strategy_state` itself is still passed by reference and
only the variant alternatives use shared_ptrs. This allows ongoing
compactions to retain ownership of the state independently of the
wrapper's lifetime.
Fixes#25913
Signed-off-by: Lakshmi Narayanan Sreethar <lakshmi.sreethar@scylladb.com>
(cherry picked from commit 18c071c94b)
45b9675d28