1bf4a84d0f
Back in ed0b409, PGPROC was split and moved to static variables in procarray.c, with procs in ProcArrayStruct replaced by an array of integers representing process numbers (pgprocnos), with -1 indicating a dead process which has yet to be removed. Access to procArray is generally done under ProcArrayLock and therefore most code does not have to concern itself with -1 entries. However, MinimumActiveBackends intentionally does not take ProcArrayLock, which means it has to be extra careful when accessing procArray. Prior to ed0b409, this was handled by checking for a NULL in the pointer array, but that check was no longer valid after the split. Coverity pointed out that the check could never happen and so it was removed in 5592eba. That didn't make anything worse, but it didn't fix the issue either. The correct fix is to check for pgprocno == -1 and skip over that entry if it is encountered. Back-patch to 9.2, since there can be attempts to access the arrays prior to their start otherwise. Note that the changes prior to 9.4 will look a bit different due to the change in 5592eba. Note that MinimumActiveBackends only returns a bool for heuristic purposes and any pre-array accesses are strictly read-only and so there is no security implication and the lack of fields complaints indicates it's very unlikely to run into issues due to this. Pointed out by Noah.
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/.