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glib/gio/gdbusauthmechanismanon.c
Simon McVittie e0a0749268 gdbusauthmechanismexternal: Optionally send empty authorization identity 
When using a GDBus client in a non-trivial user namespace, the result of
geteuid() can differ from the uid in the namespace where the server is
running. This would result in connection attempts being rejected, because
the identity that the client claims to have does not match the identity
that the server derives from its credentials.

RFC 4422 allows us to send an empty authorization identity, which means we
want to authenticate as whatever identity the server can derive from our
out-of-band credentials. In particular, this resolves the authentication
failure when crossing between different Linux user namespaces.

Because D-Bus does not have a way to represent an empty initial response
as distinct from the absence of an initial response, we cannot use the
initial-response optimization (RFC 4422 §4.3.a) in this case, and must
fall back to waiting for the server to send a challenge.

Unfortunately, GDBus versions older than glib!2826 did not implement
the server side of this protocol correctly, and would respond to the
missing initial response in a way that breaks the SASL state machine
(expecting a response without sending a challenge), causing client and
server to deadlock with each waiting for the other to respond. Until
fixed versions of GDBus are widespread, we can't rely on having a server
that can cope with this, so gate it behind a flag, which can be set for
connections that are known to cross non-trivial namespace boundaries.

Originally inspired by
<1ed4723d38>,
and based on earlier work by Giuseppe Scrivano (in which the
cross-namespace behaviour was unconditional, rather than gated by a
flag).

Co-authored-by: Giuseppe Scrivano <giuseppe@scrivano.org>
Signed-off-by: Simon McVittie <smcv@collabora.com>
2022-07-24 13:46:26 +01:00

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/* GDBus - GLib D-Bus Library
*
* Copyright (C) 2008-2010 Red Hat, Inc.
*
* SPDX-License-Identifier: LGPL-2.1-or-later
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General
* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
* Author: David Zeuthen <davidz@redhat.com>
*/
#include "config.h"
#include "gdbusauthmechanismanon.h"
#include "gdbuserror.h"
#include "gioenumtypes.h"
#include "glibintl.h"
struct _GDBusAuthMechanismAnonPrivate
{
gboolean is_client;
gboolean is_server;
GDBusAuthMechanismState state;
};
static gint mechanism_get_priority (void);
static const gchar *mechanism_get_name (void);
static gboolean mechanism_is_supported (GDBusAuthMechanism *mechanism);
static gchar *mechanism_encode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
static gchar *mechanism_decode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
static GDBusAuthMechanismState mechanism_server_get_state (GDBusAuthMechanism *mechanism);
static void mechanism_server_initiate (GDBusAuthMechanism *mechanism,
const gchar *initial_response,
gsize initial_response_len);
static void mechanism_server_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
static gchar *mechanism_server_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
static gchar *mechanism_server_get_reject_reason (GDBusAuthMechanism *mechanism);
static void mechanism_server_shutdown (GDBusAuthMechanism *mechanism);
static GDBusAuthMechanismState mechanism_client_get_state (GDBusAuthMechanism *mechanism);
static gchar *mechanism_client_initiate (GDBusAuthMechanism *mechanism,
GDBusConnectionFlags conn_flags,
gsize *out_initial_response_len);
static void mechanism_client_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
static gchar *mechanism_client_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
static void mechanism_client_shutdown (GDBusAuthMechanism *mechanism);
/* ---------------------------------------------------------------------------------------------------- */
G_DEFINE_TYPE_WITH_PRIVATE (GDBusAuthMechanismAnon, _g_dbus_auth_mechanism_anon, G_TYPE_DBUS_AUTH_MECHANISM)
/* ---------------------------------------------------------------------------------------------------- */
static void
_g_dbus_auth_mechanism_anon_finalize (GObject *object)
{
//GDBusAuthMechanismAnon *mechanism = G_DBUS_AUTH_MECHANISM_ANON (object);
if (G_OBJECT_CLASS (_g_dbus_auth_mechanism_anon_parent_class)->finalize != NULL)
G_OBJECT_CLASS (_g_dbus_auth_mechanism_anon_parent_class)->finalize (object);
}
static void
_g_dbus_auth_mechanism_anon_class_init (GDBusAuthMechanismAnonClass *klass)
{
GObjectClass *gobject_class;
GDBusAuthMechanismClass *mechanism_class;
gobject_class = G_OBJECT_CLASS (klass);
gobject_class->finalize = _g_dbus_auth_mechanism_anon_finalize;
mechanism_class = G_DBUS_AUTH_MECHANISM_CLASS (klass);
mechanism_class->get_priority = mechanism_get_priority;
mechanism_class->get_name = mechanism_get_name;
mechanism_class->is_supported = mechanism_is_supported;
mechanism_class->encode_data = mechanism_encode_data;
mechanism_class->decode_data = mechanism_decode_data;
mechanism_class->server_get_state = mechanism_server_get_state;
mechanism_class->server_initiate = mechanism_server_initiate;
mechanism_class->server_data_receive = mechanism_server_data_receive;
mechanism_class->server_data_send = mechanism_server_data_send;
mechanism_class->server_get_reject_reason = mechanism_server_get_reject_reason;
mechanism_class->server_shutdown = mechanism_server_shutdown;
mechanism_class->client_get_state = mechanism_client_get_state;
mechanism_class->client_initiate = mechanism_client_initiate;
mechanism_class->client_data_receive = mechanism_client_data_receive;
mechanism_class->client_data_send = mechanism_client_data_send;
mechanism_class->client_shutdown = mechanism_client_shutdown;
}
static void
_g_dbus_auth_mechanism_anon_init (GDBusAuthMechanismAnon *mechanism)
{
mechanism->priv = _g_dbus_auth_mechanism_anon_get_instance_private (mechanism);
}
/* ---------------------------------------------------------------------------------------------------- */
static gint
mechanism_get_priority (void)
{
/* We prefer ANONYMOUS to most other mechanism (such as DBUS_COOKIE_SHA1) but not to EXTERNAL */
return 50;
}
static const gchar *
mechanism_get_name (void)
{
return "ANONYMOUS";
}
static gboolean
mechanism_is_supported (GDBusAuthMechanism *mechanism)
{
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), FALSE);
return TRUE;
}
static gchar *
mechanism_encode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len)
{
return NULL;
}
static gchar *
mechanism_decode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len)
{
return NULL;
}
/* ---------------------------------------------------------------------------------------------------- */
static GDBusAuthMechanismState
mechanism_server_get_state (GDBusAuthMechanism *mechanism)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), G_DBUS_AUTH_MECHANISM_STATE_INVALID);
g_return_val_if_fail (m->priv->is_server && !m->priv->is_client, G_DBUS_AUTH_MECHANISM_STATE_INVALID);
return m->priv->state;
}
static void
mechanism_server_initiate (GDBusAuthMechanism *mechanism,
const gchar *initial_response,
gsize initial_response_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism));
g_return_if_fail (!m->priv->is_server && !m->priv->is_client);
//g_debug ("ANONYMOUS: initial_response was '%s'", initial_response);
m->priv->is_server = TRUE;
m->priv->state = G_DBUS_AUTH_MECHANISM_STATE_ACCEPTED;
}
static void
mechanism_server_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism));
g_return_if_fail (m->priv->is_server && !m->priv->is_client);
g_return_if_fail (m->priv->state == G_DBUS_AUTH_MECHANISM_STATE_WAITING_FOR_DATA);
/* can never end up here because we are never in the WAITING_FOR_DATA state */
g_assert_not_reached ();
}
static gchar *
mechanism_server_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), NULL);
g_return_val_if_fail (m->priv->is_server && !m->priv->is_client, NULL);
g_return_val_if_fail (m->priv->state == G_DBUS_AUTH_MECHANISM_STATE_HAVE_DATA_TO_SEND, NULL);
/* can never end up here because we are never in the HAVE_DATA_TO_SEND state */
g_assert_not_reached ();
return NULL;
}
static gchar *
mechanism_server_get_reject_reason (GDBusAuthMechanism *mechanism)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), NULL);
g_return_val_if_fail (m->priv->is_server && !m->priv->is_client, NULL);
g_return_val_if_fail (m->priv->state == G_DBUS_AUTH_MECHANISM_STATE_REJECTED, NULL);
/* can never end up here because we are never in the REJECTED state */
g_assert_not_reached ();
return NULL;
}
static void
mechanism_server_shutdown (GDBusAuthMechanism *mechanism)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism));
g_return_if_fail (m->priv->is_server && !m->priv->is_client);
m->priv->is_server = FALSE;
}
/* ---------------------------------------------------------------------------------------------------- */
static GDBusAuthMechanismState
mechanism_client_get_state (GDBusAuthMechanism *mechanism)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), G_DBUS_AUTH_MECHANISM_STATE_INVALID);
g_return_val_if_fail (m->priv->is_client && !m->priv->is_server, G_DBUS_AUTH_MECHANISM_STATE_INVALID);
return m->priv->state;
}
static gchar *
mechanism_client_initiate (GDBusAuthMechanism *mechanism,
GDBusConnectionFlags conn_flags,
gsize *out_initial_response_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
gchar *result;
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), NULL);
g_return_val_if_fail (!m->priv->is_server && !m->priv->is_client, NULL);
m->priv->is_client = TRUE;
m->priv->state = G_DBUS_AUTH_MECHANISM_STATE_ACCEPTED;
/* just return our library name and version */
result = g_strdup ("GDBus 0.1");
*out_initial_response_len = strlen (result);
return result;
}
static void
mechanism_client_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism));
g_return_if_fail (m->priv->is_client && !m->priv->is_server);
g_return_if_fail (m->priv->state == G_DBUS_AUTH_MECHANISM_STATE_WAITING_FOR_DATA);
/* can never end up here because we are never in the WAITING_FOR_DATA state */
g_assert_not_reached ();
}
static gchar *
mechanism_client_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism), NULL);
g_return_val_if_fail (m->priv->is_client && !m->priv->is_server, NULL);
g_return_val_if_fail (m->priv->state == G_DBUS_AUTH_MECHANISM_STATE_HAVE_DATA_TO_SEND, NULL);
/* can never end up here because we are never in the HAVE_DATA_TO_SEND state */
g_assert_not_reached ();
return NULL;
}
static void
mechanism_client_shutdown (GDBusAuthMechanism *mechanism)
{
GDBusAuthMechanismAnon *m = G_DBUS_AUTH_MECHANISM_ANON (mechanism);
g_return_if_fail (G_IS_DBUS_AUTH_MECHANISM_ANON (mechanism));
g_return_if_fail (m->priv->is_client && !m->priv->is_server);
m->priv->is_client = FALSE;
}
/* ---------------------------------------------------------------------------------------------------- */
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