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
script.
To do this, have pg_ctl pass down its parent shell's PID in an environment
variable PG_GRANDPARENT_PID, and teach CreateLockFile() to disregard that PID
as a false match if it finds it in postmaster.pid. This allows us to cope
with one level of postgres-owned shell process even with pg_ctl in the way,
so it's just as safe as starting the postmaster directly. You still have to
be careful about how you write the initscript though.
Adjust the comments in contrib/start-scripts/ to not deprecate use of
pg_ctl. Also, fix the ROTATELOGS option in the OSX script, which was
indulging in exactly the sort of unsafe coding that renders this fix
pointless :-(. A pipe inside the "sudo" will probably result in more
than one postgres-owned process hanging around.
