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dblink: SCRAM authentication pass-through

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This enables SCRAM authentication for dblink (using dblink_fdw) when
connecting to a foreign server without having to store a plain-text
password on user mapping options

This uses the same approach as it was implemented for postgres_fdw in
commit 761c79508e7.  (It also contains the equivalent of the
subsequent fixes 76563f88cfb and d2028e9bbc1.)

Author: Matheus Alcantara <mths.dev@pm.me>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CAFY6G8ercA1KES%3DE_0__R9QCTR805TTyYr1No8qF8ZxmMg8z2Q%40mail.gmail.com
This commit is contained in:
Peter Eisentraut 2025-03-26 10:05:49 +01:00
parent a3b6dfd410
commit 3642df265d
6 changed files with 457 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
contrib/dblink/Makefile
View File

@ -13,6 +13,7 @@ PGFILEDESC = "dblink - connect to other PostgreSQL databases"
REGRESS = dblink
REGRESS_OPTS = --dlpath=$(top_builddir)/src/test/regress
TAP_TESTS = 1
ifdef USE_PGXS
PG_CONFIG = pg_config

184
contrib/dblink/dblink.c
View File

@ -43,6 +43,8 @@
#include "catalog/pg_foreign_server.h"
#include "catalog/pg_type.h"
#include "catalog/pg_user_mapping.h"
#include "commands/defrem.h"
#include "common/base64.h"
#include "executor/spi.h"
#include "foreign/foreign.h"
#include "funcapi.h"
@ -126,6 +128,11 @@ static bool is_valid_dblink_option(const PQconninfoOption *options,
const char *option, Oid context);
static int applyRemoteGucs(PGconn *conn);
static void restoreLocalGucs(int nestlevel);
static bool UseScramPassthrough(ForeignServer *foreign_server, UserMapping *user);
static void appendSCRAMKeysInfo(StringInfo buf);
static bool is_valid_dblink_fdw_option(const PQconninfoOption *options, const char *option,
Oid context);
static bool dblink_connstr_has_required_scram_options(const char *connstr);
/* Global */
static remoteConn *pconn = NULL;
@ -1964,7 +1971,7 @@ dblink_fdw_validator(PG_FUNCTION_ARGS)
{
DefElem *def = (DefElem *) lfirst(cell);
if (!is_valid_dblink_option(options, def->defname, context))
if (!is_valid_dblink_fdw_option(options, def->defname, context))
{
/*
* Unknown option, or invalid option for the context specified, so
@ -2596,6 +2603,67 @@ deleteConnection(const char *name)
errmsg("undefined connection name")));
}
/*
* Ensure that require_auth and SCRAM keys are correctly set on connstr.
* SCRAM keys used to pass-through are coming from the initial connection
* from the client with the server.
*
* All required SCRAM options are set by dblink, so we just need to ensure
* that these options are not overwritten by the user.
*
* See appendSCRAMKeysInfo and its usage for more.
*/
bool
dblink_connstr_has_required_scram_options(const char *connstr)
{
PQconninfoOption *options;
bool has_scram_server_key = false;
bool has_scram_client_key = false;
bool has_require_auth = false;
bool has_scram_keys = false;
options = PQconninfoParse(connstr, NULL);
if (options)
{
/*
* Continue iterating even if we found the keys that we need to
* validate to make sure that there is no other declaration of these
* keys that can overwrite the first.
*/
for (PQconninfoOption *option = options; option->keyword != NULL; option++)
{
if (strcmp(option->keyword, "require_auth") == 0)
{
if (option->val != NULL && strcmp(option->val, "scram-sha-256") == 0)
has_require_auth = true;
else
has_require_auth = false;
}
if (strcmp(option->keyword, "scram_client_key") == 0)
{
if (option->val != NULL && option->val[0] != '\0')
has_scram_client_key = true;
else
has_scram_client_key = false;
}
if (strcmp(option->keyword, "scram_server_key") == 0)
{
if (option->val != NULL && option->val[0] != '\0')
has_scram_server_key = true;
else
has_scram_server_key = false;
}
}
PQconninfoFree(options);
}
has_scram_keys = has_scram_client_key && has_scram_server_key && MyProcPort->has_scram_keys;
return (has_scram_keys && has_require_auth);
}
/*
* We need to make sure that the connection made used credentials
* which were provided by the user, so check what credentials were
@ -2612,6 +2680,18 @@ dblink_security_check(PGconn *conn, remoteConn *rconn, const char *connstr)
if (PQconnectionUsedPassword(conn) && dblink_connstr_has_pw(connstr))
return;
/*
* Password was not used to connect, check if SCRAM pass-through is in
* use.
*
* If dblink_connstr_has_required_scram_options is true we assume that
* UseScramPassthrough is also true because the required SCRAM keys are
* only added if UseScramPassthrough is set, and the user is not allowed
* to add the SCRAM keys on fdw and user mapping options.
*/
if (MyProcPort->has_scram_keys && dblink_connstr_has_required_scram_options(connstr))
return;
#ifdef ENABLE_GSS
/* If GSSAPI creds used to connect, make sure it was one delegated */
if (PQconnectionUsedGSSAPI(conn) && be_gssapi_get_delegation(MyProcPort))
@ -2664,12 +2744,14 @@ dblink_connstr_has_pw(const char *connstr)
}
/*
* For non-superusers, insist that the connstr specify a password, except
* if GSSAPI credentials have been delegated (and we check that they are used
* for the connection in dblink_security_check later). This prevents a
* password or GSSAPI credentials from being picked up from .pgpass, a
* service file, the environment, etc. We don't want the postgres user's
* passwords or Kerberos credentials to be accessible to non-superusers.
* For non-superusers, insist that the connstr specify a password, except if
* GSSAPI credentials have been delegated (and we check that they are used for
* the connection in dblink_security_check later) or if SCRAM pass-through is
* being used. This prevents a password or GSSAPI credentials from being
* picked up from .pgpass, a service file, the environment, etc. We don't want
* the postgres user's passwords or Kerberos credentials to be accessible to
* non-superusers. In case of SCRAM pass-through insist that the connstr
* has the required SCRAM pass-through options.
*/
static void
dblink_connstr_check(const char *connstr)
@ -2680,6 +2762,9 @@ dblink_connstr_check(const char *connstr)
if (dblink_connstr_has_pw(connstr))
return;
if (MyProcPort->has_scram_keys && dblink_connstr_has_required_scram_options(connstr))
return;
#ifdef ENABLE_GSS
if (be_gssapi_get_delegation(MyProcPort))
return;
@ -2832,6 +2917,14 @@ get_connect_string(const char *servername)
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, OBJECT_FOREIGN_SERVER, foreign_server->servername);
/*
* First append hardcoded options needed for SCRAM pass-through, so if
* the user overwrites these options we can ereport on
* dblink_connstr_check and dblink_security_check.
*/
if (MyProcPort->has_scram_keys && UseScramPassthrough(foreign_server, user_mapping))
appendSCRAMKeysInfo(&buf);
foreach(cell, fdw->options)
{
DefElem *def = lfirst(cell);
@ -3016,6 +3109,20 @@ is_valid_dblink_option(const PQconninfoOption *options, const char *option,
return true;
}
/*
* Same as is_valid_dblink_option but also check for only dblink_fdw specific
* options.
*/
static bool
is_valid_dblink_fdw_option(const PQconninfoOption *options, const char *option,
Oid context)
{
if (strcmp(option, "use_scram_passthrough") == 0)
return true;
return is_valid_dblink_option(options, option, context);
}
/*
* Copy the remote session's values of GUCs that affect datatype I/O
* and apply them locally in a new GUC nesting level. Returns the new
@ -3085,3 +3192,66 @@ restoreLocalGucs(int nestlevel)
if (nestlevel > 0)
AtEOXact_GUC(true, nestlevel);
}
/*
* Append SCRAM client key and server key information from the global
* MyProcPort into the given StringInfo buffer.
*/
static void
appendSCRAMKeysInfo(StringInfo buf)
{
int len;
int encoded_len;
char *client_key;
char *server_key;
len = pg_b64_enc_len(sizeof(MyProcPort->scram_ClientKey));
/* don't forget the zero-terminator */
client_key = palloc0(len + 1);
encoded_len = pg_b64_encode((const char *) MyProcPort->scram_ClientKey,
sizeof(MyProcPort->scram_ClientKey),
client_key, len);
if (encoded_len < 0)
elog(ERROR, "could not encode SCRAM client key");
len = pg_b64_enc_len(sizeof(MyProcPort->scram_ServerKey));
/* don't forget the zero-terminator */
server_key = palloc0(len + 1);
encoded_len = pg_b64_encode((const char *) MyProcPort->scram_ServerKey,
sizeof(MyProcPort->scram_ServerKey),
server_key, len);
if (encoded_len < 0)
elog(ERROR, "could not encode SCRAM server key");
appendStringInfo(buf, "scram_client_key='%s' ", client_key);
appendStringInfo(buf, "scram_server_key='%s' ", server_key);
appendStringInfo(buf, "require_auth='scram-sha-256' ");
pfree(client_key);
pfree(server_key);
}
static bool
UseScramPassthrough(ForeignServer *foreign_server, UserMapping *user)
{
ListCell *cell;
foreach(cell, foreign_server->options)
{
DefElem *def = lfirst(cell);
if (strcmp(def->defname, "use_scram_passthrough") == 0)
return defGetBoolean(def);
}
foreach(cell, user->options)
{
DefElem *def = (DefElem *) lfirst(cell);
if (strcmp(def->defname, "use_scram_passthrough") == 0)
return defGetBoolean(def);
}
return false;
}

5
contrib/dblink/meson.build
View File

@ -36,4 +36,9 @@ tests += {
],
'regress_args': ['--dlpath', meson.build_root() / 'src/test/regress'],
},
'tap': {
'tests': [
't/001_auth_scram.pl',
],
},
}

254
contrib/dblink/t/001_auth_scram.pl Normal file
View File

@ -0,0 +1,254 @@
# Copyright (c) 2024-2025, PostgreSQL Global Development Group
# Test SCRAM authentication when opening a new connection with a foreign
# server.
#
# The test is executed by testing the SCRAM authentifcation on a loopback
# connection on the same server and with different servers.
use strict;
use warnings FATAL => 'all';
use PostgreSQL::Test::Utils;
use PostgreSQL::Test::Cluster;
use Test::More;
if (!$use_unix_sockets)
{
plan skip_all => "test requires Unix-domain sockets";
}
my $user = "user01";
my $db0 = "db0"; # For node1
my $db1 = "db1"; # For node1
my $db2 = "db2"; # For node2
my $fdw_server = "db1_fdw";
my $fdw_server2 = "db2_fdw";
my $fdw_invalid_server = "db2_fdw_invalid"; # For invalid fdw options
my $fdw_invalid_server2 =
"db2_fdw_invalid2"; # For invalid scram keys fdw options
my $node1 = PostgreSQL::Test::Cluster->new('node1');
my $node2 = PostgreSQL::Test::Cluster->new('node2');
$node1->init;
$node2->init;
$node1->start;
$node2->start;
# Test setup
$node1->safe_psql('postgres', qq'CREATE USER $user WITH password \'pass\'');
$node2->safe_psql('postgres', qq'CREATE USER $user WITH password \'pass\'');
$ENV{PGPASSWORD} = "pass";
$node1->safe_psql('postgres', qq'CREATE DATABASE $db0');
$node1->safe_psql('postgres', qq'CREATE DATABASE $db1');
$node2->safe_psql('postgres', qq'CREATE DATABASE $db2');
setup_table($node1, $db1, "t");
setup_table($node2, $db2, "t2");
$node1->safe_psql($db0, 'CREATE EXTENSION IF NOT EXISTS dblink');
setup_fdw_server($node1, $db0, $fdw_server, $node1, $db1);
setup_fdw_server($node1, $db0, $fdw_server2, $node2, $db2);
setup_invalid_fdw_server($node1, $db0, $fdw_invalid_server, $node2, $db2);
setup_fdw_server($node1, $db0, $fdw_invalid_server2, $node2, $db2);
setup_user_mapping($node1, $db0, $fdw_server);
setup_user_mapping($node1, $db0, $fdw_server2);
setup_user_mapping($node1, $db0, $fdw_invalid_server);
# Make the user have the same SCRAM key on both servers. Forcing to have the
# same iteration and salt.
my $rolpassword = $node1->safe_psql('postgres',
qq"SELECT rolpassword FROM pg_authid WHERE rolname = '$user';");
$node2->safe_psql('postgres', qq"ALTER ROLE $user PASSWORD '$rolpassword'");
unlink($node1->data_dir . '/pg_hba.conf');
unlink($node2->data_dir . '/pg_hba.conf');
$node1->append_conf(
'pg_hba.conf', qq{
local db0 all scram-sha-256
local db1 all scram-sha-256
}
);
$node2->append_conf(
'pg_hba.conf', qq{
local db2 all scram-sha-256
}
);
$node1->restart;
$node2->restart;
# End of test setup
test_scram_keys_is_not_overwritten($node1, $db0, $fdw_invalid_server2);
test_fdw_auth($node1, $db0, "t", $fdw_server,
"SCRAM auth on the same database cluster must succeed");
test_fdw_auth($node1, $db0, "t2", $fdw_server2,
"SCRAM auth on a different database cluster must succeed");
test_fdw_auth_with_invalid_overwritten_require_auth($fdw_invalid_server);
# Ensure that trust connections fail without superuser opt-in.
unlink($node1->data_dir . '/pg_hba.conf');
unlink($node2->data_dir . '/pg_hba.conf');
$node1->append_conf(
'pg_hba.conf', qq{
local db0 all scram-sha-256
local db1 all trust
}
);
$node2->append_conf(
'pg_hba.conf', qq{
local all all password
}
);
$node1->restart;
$node2->restart;
my ($ret, $stdout, $stderr) = $node1->psql(
$db0,
"SELECT * FROM dblink('$fdw_server', 'SELECT * FROM t') AS t(a int, b int)",
connstr => $node1->connstr($db0) . " user=$user");
is($ret, 3, 'loopback trust fails on the same cluster');
like(
$stderr,
qr/failed: authentication method requirement "scram-sha-256" failed: server did not complete authentication/,
'expected error from loopback trust (same cluster)');
($ret, $stdout, $stderr) = $node1->psql(
$db0,
"SELECT * FROM dblink('$fdw_server2', 'SELECT * FROM t2') AS t2(a int, b int)",
connstr => $node1->connstr($db0) . " user=$user");
is($ret, 3, 'loopback password fails on a different cluster');
like(
$stderr,
qr/authentication method requirement "scram-sha-256" failed: server requested a cleartext password/,
'expected error from loopback password (different cluster)');
# Helper functions
sub test_fdw_auth
{
local $Test::Builder::Level = $Test::Builder::Level + 1;
my ($node, $db, $tbl, $fdw, $testname) = @_;
my $connstr = $node->connstr($db) . qq' user=$user';
my $ret = $node->safe_psql(
$db,
qq"SELECT count(1) FROM dblink('$fdw', 'SELECT * FROM $tbl') AS $tbl(a int, b int)",
connstr => $connstr);
is($ret, '10', $testname);
}
sub test_fdw_auth_with_invalid_overwritten_require_auth
{
local $Test::Builder::Level = $Test::Builder::Level + 1;
my ($fdw) = @_;
my ($ret, $stdout, $stderr) = $node1->psql(
$db0,
"select * from dblink('$fdw', 'select * from t') as t(a int, b int)",
connstr => $node1->connstr($db0) . " user=$user");
is($ret, 3, 'loopback trust fails when overwriting require_auth');
like(
$stderr,
qr/password or GSSAPI delegated credentials required/,
'expected error when connecting to a fdw overwriting the require_auth'
);
}
sub test_scram_keys_is_not_overwritten
{
local $Test::Builder::Level = $Test::Builder::Level + 1;
my ($node, $db, $fdw) = @_;
my ($ret, $stdout, $stderr) = $node->psql(
$db,
qq'CREATE USER MAPPING FOR $user SERVER $fdw OPTIONS (user \'$user\', scram_client_key \'key\');',
connstr => $node->connstr($db) . " user=$user");
is($ret, 3, 'user mapping creation fails when using scram_client_key');
like(
$stderr,
qr/ERROR: invalid option "scram_client_key"/,
'user mapping creation fails when using scram_client_key');
($ret, $stdout, $stderr) = $node->psql(
$db,
qq'CREATE USER MAPPING FOR $user SERVER $fdw OPTIONS (user \'$user\', scram_server_key \'key\');',
connstr => $node->connstr($db) . " user=$user");
is($ret, 3, 'user mapping creation fails when using scram_server_key');
like(
$stderr,
qr/ERROR: invalid option "scram_server_key"/,
'user mapping creation fails when using scram_server_key');
}
sub setup_user_mapping
{
my ($node, $db, $fdw) = @_;
$node->safe_psql($db,
qq'CREATE USER MAPPING FOR $user SERVER $fdw OPTIONS (user \'$user\');'
);
}
sub setup_fdw_server
{
my ($node, $db, $fdw, $fdw_node, $dbname) = @_;
my $host = $fdw_node->host;
my $port = $fdw_node->port;
$node->safe_psql(
$db, qq'CREATE SERVER $fdw FOREIGN DATA WRAPPER dblink_fdw options (
host \'$host\', port \'$port\', dbname \'$dbname\', use_scram_passthrough \'true\') '
);
$node->safe_psql($db, qq'GRANT USAGE ON FOREIGN SERVER $fdw TO $user;');
$node->safe_psql($db, qq'GRANT ALL ON SCHEMA public TO $user');
}
sub setup_invalid_fdw_server
{
my ($node, $db, $fdw, $fdw_node, $dbname) = @_;
my $host = $fdw_node->host;
my $port = $fdw_node->port;
$node->safe_psql(
$db, qq'CREATE SERVER $fdw FOREIGN DATA WRAPPER dblink_fdw options (
host \'$host\', port \'$port\', dbname \'$dbname\', use_scram_passthrough \'true\', require_auth \'none\') '
);
$node->safe_psql($db, qq'GRANT USAGE ON FOREIGN SERVER $fdw TO $user;');
$node->safe_psql($db, qq'GRANT ALL ON SCHEMA public TO $user');
}
sub setup_table
{
my ($node, $db, $tbl) = @_;
$node->safe_psql($db,
qq'CREATE TABLE $tbl AS SELECT g as a, g + 1 as b FROM generate_series(1,10) g(g)'
);
$node->safe_psql($db, qq'GRANT USAGE ON SCHEMA public TO $user');
$node->safe_psql($db, qq'GRANT SELECT ON $tbl TO $user');
}
done_testing();

21
doc/src/sgml/dblink.sgml
View File

@ -150,9 +150,23 @@ dblink_connect(text connname, text connstr) returns text
executing arbitrary SQL commands.
</para>
<para>
The foreign-data wrapper <filename>dblink_fdw</filename> has an additional
Boolean option <literal>use_scram_passthrough</literal> that controls
whether <filename>dblink</filename> will use the SCRAM pass-through
authentication to connect to the remote database. With SCRAM pass-through
authentication, <filename>dblink</filename> uses SCRAM-hashed secrets
instead of plain-text user passwords to connect to the remote server. This
avoids storing plain-text user passwords in PostgreSQL system catalogs.
See the documentation of the equivalent <link
linkend="postgres-fdw-option-use-scram-passthrough"><literal>use_scram_passthrough</literal></link>
option of postgres_fdw for further details and restrictions.
</para>
<para>
Only superusers may use <function>dblink_connect</function> to create
non-password-authenticated and non-GSSAPI-authenticated connections.
connections that use neither password authentication, SCRAM pass-through,
nor GSSAPI-authentication.
If non-superusers need this capability, use
<function>dblink_connect_u</function> instead.
</para>
@ -181,8 +195,9 @@ SELECT dblink_connect('myconn', 'dbname=postgres options=-csearch_path=');
(1 row)
-- FOREIGN DATA WRAPPER functionality
-- Note: local connection must require password authentication for this to work properly
-- Otherwise, you will receive the following error from dblink_connect():
-- Note: local connections that don't use SCRAM pass-through require password
-- authentication for this to work properly. Otherwise, you will receive
-- the following error from dblink_connect():
-- ERROR: password is required
-- DETAIL: Non-superuser cannot connect if the server does not request a password.
-- HINT: Target server's authentication method must be changed.

4
doc/src/sgml/postgres-fdw.sgml
View File

@ -756,7 +756,7 @@ OPTIONS (ADD password_required 'false');
<variablelist>
<varlistentry>
<varlistentry id="postgres-fdw-option-keep-connections">
<term><literal>keep_connections</literal> (<type>boolean</type>)</term>
<listitem>
<para>
@ -770,7 +770,7 @@ OPTIONS (ADD password_required 'false');
</listitem>
</varlistentry>
<varlistentry>
<varlistentry id="postgres-fdw-option-use-scram-passthrough">
<term><literal>use_scram_passthrough</literal> (<type>boolean</type>)</term>
<listitem>
<para>