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glib/gio/gdbusauthmechanism.h
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>
*/
#ifndef __G_DBUS_AUTH_MECHANISM_H__
#define __G_DBUS_AUTH_MECHANISM_H__
#if !defined (GIO_COMPILATION)
#error "gdbusauthmechanism.h is a private header file."
#endif
#include <gio/giotypes.h>
G_BEGIN_DECLS
#define G_TYPE_DBUS_AUTH_MECHANISM (_g_dbus_auth_mechanism_get_type ())
#define G_DBUS_AUTH_MECHANISM(o) (G_TYPE_CHECK_INSTANCE_CAST ((o), G_TYPE_DBUS_AUTH_MECHANISM, GDBusAuthMechanism))
#define G_DBUS_AUTH_MECHANISM_CLASS(k) (G_TYPE_CHECK_CLASS_CAST((k), G_TYPE_DBUS_AUTH_MECHANISM, GDBusAuthMechanismClass))
#define G_DBUS_AUTH_MECHANISM_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), G_TYPE_DBUS_AUTH_MECHANISM, GDBusAuthMechanismClass))
#define G_IS_DBUS_AUTH_MECHANISM(o) (G_TYPE_CHECK_INSTANCE_TYPE ((o), G_TYPE_DBUS_AUTH_MECHANISM))
#define G_IS_DBUS_AUTH_MECHANISM_CLASS(k) (G_TYPE_CHECK_CLASS_TYPE ((k), G_TYPE_DBUS_AUTH_MECHANISM))
typedef struct _GDBusAuthMechanism GDBusAuthMechanism;
typedef struct _GDBusAuthMechanismClass GDBusAuthMechanismClass;
typedef struct _GDBusAuthMechanismPrivate GDBusAuthMechanismPrivate;
typedef enum {
G_DBUS_AUTH_MECHANISM_STATE_INVALID,
G_DBUS_AUTH_MECHANISM_STATE_WAITING_FOR_DATA,
G_DBUS_AUTH_MECHANISM_STATE_HAVE_DATA_TO_SEND,
G_DBUS_AUTH_MECHANISM_STATE_REJECTED,
G_DBUS_AUTH_MECHANISM_STATE_ACCEPTED,
} GDBusAuthMechanismState;
struct _GDBusAuthMechanismClass
{
/*< private >*/
GObjectClass parent_class;
/*< public >*/
/* VTable */
/* TODO: server_initiate and client_initiate probably needs to have a
* GCredentials parameter...
*/
gint (*get_priority) (void);
const gchar *(*get_name) (void);
/* functions shared by server/client */
gboolean (*is_supported) (GDBusAuthMechanism *mechanism);
gchar *(*encode_data) (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
gchar *(*decode_data) (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
/* functions for server-side authentication */
GDBusAuthMechanismState (*server_get_state) (GDBusAuthMechanism *mechanism);
void (*server_initiate) (GDBusAuthMechanism *mechanism,
const gchar *initial_response,
gsize initial_response_len);
void (*server_data_receive) (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
gchar *(*server_data_send) (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
gchar *(*server_get_reject_reason) (GDBusAuthMechanism *mechanism);
void (*server_shutdown) (GDBusAuthMechanism *mechanism);
/* functions for client-side authentication */
GDBusAuthMechanismState (*client_get_state) (GDBusAuthMechanism *mechanism);
gchar *(*client_initiate) (GDBusAuthMechanism *mechanism,
GDBusConnectionFlags conn_flags,
gsize *out_initial_response_len);
void (*client_data_receive) (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
gchar *(*client_data_send) (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
void (*client_shutdown) (GDBusAuthMechanism *mechanism);
};
struct _GDBusAuthMechanism
{
GObject parent_instance;
GDBusAuthMechanismPrivate *priv;
};
GType _g_dbus_auth_mechanism_get_type (void) G_GNUC_CONST;
gint _g_dbus_auth_mechanism_get_priority (GType mechanism_type);
const gchar *_g_dbus_auth_mechanism_get_name (GType mechanism_type);
GIOStream *_g_dbus_auth_mechanism_get_stream (GDBusAuthMechanism *mechanism);
GCredentials *_g_dbus_auth_mechanism_get_credentials (GDBusAuthMechanism *mechanism);
gboolean _g_dbus_auth_mechanism_is_supported (GDBusAuthMechanism *mechanism);
gchar *_g_dbus_auth_mechanism_encode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
gchar *_g_dbus_auth_mechanism_decode_data (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len,
gsize *out_data_len);
GDBusAuthMechanismState _g_dbus_auth_mechanism_server_get_state (GDBusAuthMechanism *mechanism);
void _g_dbus_auth_mechanism_server_initiate (GDBusAuthMechanism *mechanism,
const gchar *initial_response,
gsize initial_response_len);
void _g_dbus_auth_mechanism_server_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
gchar *_g_dbus_auth_mechanism_server_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
gchar *_g_dbus_auth_mechanism_server_get_reject_reason (GDBusAuthMechanism *mechanism);
void _g_dbus_auth_mechanism_server_shutdown (GDBusAuthMechanism *mechanism);
GDBusAuthMechanismState _g_dbus_auth_mechanism_client_get_state (GDBusAuthMechanism *mechanism);
gchar *_g_dbus_auth_mechanism_client_initiate (GDBusAuthMechanism *mechanism,
GDBusConnectionFlags conn_flags,
gsize *out_initial_response_len);
void _g_dbus_auth_mechanism_client_data_receive (GDBusAuthMechanism *mechanism,
const gchar *data,
gsize data_len);
gchar *_g_dbus_auth_mechanism_client_data_send (GDBusAuthMechanism *mechanism,
gsize *out_data_len);
void _g_dbus_auth_mechanism_client_shutdown (GDBusAuthMechanism *mechanism);
G_END_DECLS
#endif /* __G_DBUS_AUTH_MECHANISM_H__ */
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