[BTS-2216] Fix use-after-free in prepareQuery #21929
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…-2216-use-after-free-during-prepare
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Scope & Purpose
A use-after-free in prepareQuery, introduced in #21080.
Since #21080,
Query::prepareQueryis a coroutine, but its callerQuery::executestill returns WAITING for suspension. This was translated, so thatprepareQueryfinished caused a wakeup, resumingexecute. Mostly, no other wakeups can occur during that time; but for a kill, which can trigger a wakeup if the query has DBServer snippets, and cause the query to be destroyed whileprepareQueryis still running.In this PR,
Query::executeis refactored into a coroutine to prevent this race. The WAITING->coro glue code is therefore moved from theRestCursorHandlerintoexecute. Additional cases for synchronous calls (Query::executeSync) are now necessary in the same places, to avoid needing additional threads.Checklist
There was no release since its introduction, so no changelog entry nor backports.
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