25b692568f
A before-update row trigger may choose to return the "new" or "old" tuple unmodified. ExecBRUpdateTriggers failed to consider the second possibility, and would proceed to free the "old" tuple even if it was the one returned, leading to subsequent access to already-deallocated memory. In debug builds this reliably leads to an "invalid memory alloc request size" failure; in production builds it might accidentally work, but data corruption is also possible. This is a very old bug. There are probably a couple of reasons it hasn't been noticed up to now. It would be more usual to return NULL if one wanted to suppress the update action; returning "old" is significantly less efficient since the update will occur anyway. Also, none of the standard PLs would ever cause this because they all returned freshly-manufactured tuples even if they were just copying "old". But commit 4b93f5799 changed that for plpgsql, making it possible to see the bug with a plpgsql trigger. Still, this is certainly legal behavior for a trigger function, so it's ExecBRUpdateTriggers's fault not plpgsql's. It seems worth creating a test case that exercises returning "old" directly with a C-language trigger; testing this through plpgsql seems unreliable because its behavior might change again. Report and fix by Rushabh Lathia; regression test case by me. Back-patch to all supported branches. Discussion: https://postgr.es/m/CAGPqQf1P4pjiNPrMof=P_16E-DFjt457j+nH2ex3=nBTew7tXw@mail.gmail.com
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/.