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An index-only scan filled its result slot from the HeapTuple an index AM returns in scan->xs_hitup by deforming it with the virtual slot's own tuple descriptor (during GiST and SP-GiST index-only scans). But index AMs form that heap tuple using their own descriptor, scan->xs_hitupdesc. The AM's descriptor may disagree with the IoS virtual slot's descriptor about each column's precise alignment, leading to "can't happen" errors in certain rare edge cases. Hard crashes were possible but much less likely. To fix, deform the tuple with the descriptor it was formed with. This is simpler, and makes xs_hitup handling (used by GiST and SP-GiST) uniform with the nearby existing xs_itup handling (used by nbtree). In practice this issue was very unlikely to be hit (it was found during testing of a patch that will change the table AM API used during index scans). The only currently affected core opclass is GiST's range_ops. It was only possible for the datum to be accessed at an incorrectly aligned offset when reading the second or subsequent column from a multicolumn GiST index. This couldn't happen in the common case where the datum used an unaligned short varlena header. Moreover, an earlier column had to leave the range datum at an offset where the two alignments actually disagree (e.g., an odd-length varlena datum). Author: Peter Geoghegan <pg@bowt.ie> Reviewed-by: Tomas Vondra <tomas@vondra.me> Discussion: https://postgr.es/m/CAH2-WzkGXa2SKnebdW29RT1hCcQBo_p03v3iqif2u9bjzLB-aQ@mail.gmail.com Backpatch-through: 14
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.