Tom Lane wrote:
Joe Conway <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
Would it be sensible to change dblink so that unless invoked by a
superuser, it fails any connection attempt in which no password is
demanded?  I am not sure that this is possible without changes to libpq;
but ignoring implementation difficulties, is this a sane idea from
the standpoint of security and usability?


Possibly so. Remember that dblink is simply a libpq client. Doesn't that mean that similar (although likely less severe) issues affect other libpq clients executing locally, such as php or perl-dbi clients?

Yeah, in principle this issue applies to any process performing a
Postgres connection on behalf of someone else.  (Whether there are any
programs doing that, other than dblink, is debatable; but someday there
may be.)

Well certainly dbi-link has the exact same issue. And a local php-apache instance connecting to Postgres would allow Postgres connections as the apache user, no? Not that it is likely to be a problem, but if for some reason there was an apache user in Postgres, and even worse, if that user was given superuser status, you would have the exact same problem.

The point about Kerberos delegation is interesting, but given that it
doesn't work anyway, I'm not sure we need a solution for it right now.
Possibly, when and if we get around to implementing it, we can somehow
treat use of a delegated ticket as equivalent to use of a password.
The general point is that we'd like to know whether the connection was
authorized by means of some data supplied by the client, or on the basis
of our own process identity (the latter being the case we wish to
reject).  Right now the only kind of "data supplied by the client" here
is a password.

Here's a straw-man proposal that we could perhaps do for 8.3:

1. Invent a libpq connection-status function

        bool PQconnectionUsedPassword(const PGconn *conn);

Maybe PQconnectionUsedAuthToken() to mean "data supplied by the client", including other potential future mechanisms?

2. Make dblink close the connection and throw error if called by a
non-superuser and PQconnectionUsedPassword returns false.

Sounds good to me.

This idea isn't usable as a back-patch, however, because adding
functions to existing libpq versions is too chancy.  What we could
possibly do in back versions is, if dblink_connect is called by a
non-superuser, first issue the connection attempt without any password
and reject if that doesn't fail.  (This'd involve parsing the connect
string well enough to remove the password, which is tedious, but
certainly doable.)

Why not just require the connect string to contain a password for non-superusers?

I like this approach better than removing public execute privileges
on the functions, for two reasons:

* A routine minor version update would install the security fix into
existing installations, without need for any DBA intervention.

* It does not take away functionality that has perfectly legitimate uses.

Agreed.

I won't have time to work on this until the end of the coming week -- tomorrow is the last day of my current business trip which tends to be busy. Tuesday I spend all day getting from Germany to San Diego. If it can wait that long, I'll look into it starting on the 5th, unless someone beats me to it.

Joe

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