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The previous coding copied garbage into a local variable, pretty much ensuring that the intended test of an IPv6 connection address against a promoted IPv4 address from pg_hba.conf would never match. The lack of field complaints likely indicates that nobody realized this was supposed to work, which is unsurprising considering that no user-facing docs suggest it should work. In principle this could have led to a SIGSEGV due to reading off the end of memory, but since the source address would have pointed to somewhere in the function's stack frame, that's quite unlikely. What led to discovery of the bug is Hugo Osvaldo Barrera's report of a crash after an OS upgrade, which is probably because he is now running a system in which memcpy raises abort() upon detecting overlapping source and destination areas. (You'd have to additionally suppose some things about the stack frame layout to arrive at this conclusion, but it seems plausible.) This has been broken since the code was added, in commit f3aec2c7f51904e7, so back-patch to all supported branches.
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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.