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{180274222}: Don't let a temp btree become the thread's table btree - #6413
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sqlite3BtreeCursor() set thd->bt to whatever btree the thread opened its first cursor on, temporary ones included. When that temp btree was closed, sqlite3BtreeClose() only cleared thd->bttmp (if/else-if), so thd->bt was left pointing at freed memory for the life of the SQL thread. Anything walking thd->bt->cursors then missed the real table cursors. In a chunked transaction, chunk_transaction() failed to clear cur->shadtbl before the chunk commit freed the shadow tables, and the next insert dereferenced the freed shadow table in osql_save_insrec(). It reproduces with a query whose first cursor is on a temp table (e.g. "select 1 union select 2") on a fresh SQL thread, followed by a chunked INSERT ... SELECT spanning more than one chunk. Only set thd->bt for non-temporary btrees, and clear thd->bt and thd->bttmp independently on close. Signed-off-by: Salil Chandra <schandra107@bloomberg.net>
roborivers
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Oct 27, 2026
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Cbuild submission: Success ✓.
Regression testing: Success ✓.
markhannum
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Oct 27, 2026
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sqlite3BtreeCursor() set thd->bt to whatever btree the thread opened its first cursor on, temporary ones included. When that temp btree was closed, sqlite3BtreeClose() only cleared thd->bttmp (if/else-if), so thd->bt was left pointing at freed memory for the life of the SQL thread.
Anything walking thd->bt->cursors then missed the real table cursors. In a chunked transaction, chunk_transaction() failed to clear cur->shadtbl before the chunk commit freed the shadow tables, and the next insert dereferenced the freed shadow table in osql_save_insrec(). It reproduces with a query whose first cursor is on a temp table (e.g. "select 1 union select 2") on a fresh SQL thread, followed by a chunked INSERT ... SELECT spanning more than one chunk.
Only set thd->bt for non-temporary btrees, and clear thd->bt and thd->bttmp independently on close.