[Bug] Heap Use After Free in parallel_vacuum_reset_dead_items Function

Hi Developers,
     We have discovered a bug in the parallel_vacuum_reset_dead_items function in PG v17.2. Specifically:

TidStoreDestroy(dead_items) frees the dead_items pointer.

The pointer is reinitialized using TidStoreCreateShared().

However, the code later accesses the freed pointer instead of the newly reinitialized pvs->dead_items, as seen in these lines:


           pvs->shared->dead_items_dsa_handle = dsa_get_handle(TidStoreGetDSA(dead_items));

           pvs->shared->dead_items_handle = TidStoreGetHandle(dead_items);

        

       This can lead to undefined behaviour or crashes due to the use of invalid memory.



       Caught this issue while running the existing regression tests from vacuum_parallel.sql with our custom malloc allocator implementation. 

       For your reference, we have previously shared our custom malloc allocator implementation in a separate bug fix. (message ID: ).



Failed regression:

SET max_parallel_maintenance_workers TO 4;

SET min_parallel_index_scan_size TO '128kB';



CREATE TABLE parallel_vacuum_table (a int) WITH (autovacuum_enabled = off);

INSERT INTO parallel_vacuum_table SELECT i from generate_series(1, 10000) i;



CREATE INDEX regular_sized_index ON parallel_vacuum_table(a);

CREATE INDEX typically_sized_index ON parallel_vacuum_table(a);

CREATE INDEX vacuum_in_leader_small_index ON parallel_vacuum_table((1));



DELETE FROM parallel_vacuum_table;

VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;







Please let me know if you have any questions or would like further details.



Thanks & Regards,

Vallimaharajan G

Member Technical Staff

ZOHO Corporation