There exists a crash that could easily be used as a denial of service against PostgreSQL by any user who can call a trusted stored procedure that makes use of temp tables.
What this is actually exposing is a case where CurrentResourceOwner is
left pointing at garbage. PortalRun saves and restores the caller's
value of CurrentResourceOwner, which is normally fine and dandy.
When doing a top-level command such as the VACUUM, CurrentResourceOwner
is TopTransactionResourceOwner. However, VACUUM does internal
CommitTransaction and StartTransaction commands, which destroy and
recreate the whole transaction including TopTransactionResourceOwner.
In many situations TopTransactionResourceOwner ends up getting recreated
at the same address it was at before, but this is obviously not
guaranteeable in the general case; Sean's test case simply exposes one
path in which it isn't at the same address.
FYI, I can confirm that your commit fixes this issue. Thank you very much! -sc
-- Sean Chittenden
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