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By default, $PGUSER has permission to unlink $PGLOG. If $PGUSER replaces $PGLOG with a symbolic link, the server will corrupt the link-targeted file by appending log messages. Since these scripts open $PGLOG as root, the attack works regardless of target file ownership. "make install" does not install these scripts anywhere. Users having manually installed them in the past should repeat that process to acquire this fix. Most script users have $PGLOG writable to root only, located in $PGDATA. Just before updating one of these scripts, such users should rename $PGLOG to $PGLOG.old. The script will then recreate $PGLOG with proper ownership. Reviewed by Peter Eisentraut. Reported by Antoine Scemama. Security: CVE-2017-12172
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.