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In WAL receiver and WAL server, some accesses to their corresponding shared memory control structs were done without holding any kind of lock, which could lead to inconsistent and possibly insecure results. In walsender, fix by clarifying the locking rules and following them correctly, as documented in the new comment in walsender_private.h; namely that some members can be read in walsender itself without a lock, because the only writes occur in the same process. The rest of the struct requires spinlock for accesses, as usual. In walreceiver, fix by always holding spinlock while accessing the struct. While there is potentially a problem in all branches, it is minor in stable ones. This only became a real problem in pg10 because of quorum commit in synchronous replication (commit3901fd70cc), and a potential security problem in walreceiver because a superuser() check was removed by default monitoring roles (commit25fff40798). Thus, no backpatch. In passing, clean up some leftover braces which were used to create unconditional blocks. Once upon a time these were used for volatile-izing accesses to those shmem structs, which is no longer required. Many other occurrences of this pattern remain. Author: Michaël Paquier Reported-by: Michaël Paquier Reviewed-by: Masahiko Sawada, Kyotaro Horiguchi, Thomas Munro, Robert Haas Discussion: https://postgr.es/m/CAB7nPqTWYqtzD=LN_oDaf9r-hAjUEPAy0B9yRkhcsLdRN8fzrw@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/.