72b8507db2
For pass-by-reference types, the code added in 0b053e78b, which aimed to resolve a memory leak, was overly aggressive in resetting the per-tuple memory context which could result in pfree'd memory being accessed resulting in failing to find previously cached results in the hash table. What was happening was prepare_probe_slot() was switching to the per-tuple memory context and calling ExecEvalExpr(). ExecEvalExpr() may have required a memory allocation. Both MemoizeHash_hash() and MemoizeHash_equal() were aggressively resetting the per-tuple context and after determining the hash value, the context would have gotten reset before MemoizeHash_equal() was called. This could have resulted in MemoizeHash_equal() looking at pfree'd memory. This is less likely to have caused issues on a production build as some other allocation would have had to have reused the pfree'd memory to overwrite it. Otherwise, the original contents would have been intact. However, this clearly caused issues on MEMORY_CONTEXT_CHECKING builds. Author: Tender Wang, Andrei Lepikhov Reported-by: Tender Wang (using SQLancer) Reviewed-by: Andrei Lepikhov, Richard Guo, David Rowley Discussion: https://postgr.es/m/CAHewXNnT6N6UJkya0z-jLFzVxcwGfeRQSfhiwA+NyLg-x8iGew@mail.gmail.com Backpatch-through: 14, where Memoize was added
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/.