dblink_connect_u(text connstr) returns text dblink_connect_u(text connname, text connstr) returns text
dblink_connect_u() is identical to
dblink_connect(), except that it will allow non-superusers
to connect using any authentication method.
If the remote server selects an authentication method that does not
involve a password, then impersonation and subsequent escalation of
privileges can occur, because the session will appear to have
originated from the user as which the local PostgreSQL
server runs. Also, even if the remote server does demand a password,
it is possible for the password to be supplied from the server
environment, such as a ~/.pgpass file belonging to the
server's user. This opens not only a risk of impersonation, but the
possibility of exposing a password to an untrustworthy remote server.
Therefore, dblink_connect_u() is initially
installed with all privileges revoked from PUBLIC,
making it un-callable except by superusers. In some situations
it may be appropriate to grant EXECUTE permission for
dblink_connect_u() to specific users who are considered
trustworthy, but this should be done with care. It is also recommended
that any ~/.pgpass file belonging to the server's user
not contain any records specifying a wildcard host name.
For further details see dblink_connect().