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glib2.0-2.60.2-1.5.mga7.src.rpm

From ef1035d9d86464ea0b5dde60a7a0e190895fdf5b Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 14 Oct 2019 08:22:24 +0100
Subject: [PATCH 1/4] gcredentialsprivate: Document the various private macros

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 gio/gcredentialsprivate.h | 59 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/gio/gcredentialsprivate.h b/gio/gcredentialsprivate.h
index 4d1c420a8..06f0aed19 100644
--- a/gio/gcredentialsprivate.h
+++ b/gio/gcredentialsprivate.h
@@ -22,6 +22,65 @@
 #include "gio/gcredentials.h"
 #include "gio/gnetworking.h"
 
+/*
+ * G_CREDENTIALS_SUPPORTED:
+ *
+ * Defined to 1 if GCredentials works.
+ */
+#undef G_CREDENTIALS_SUPPORTED
+
+/*
+ * G_CREDENTIALS_USE_LINUX_UCRED, etc.:
+ *
+ * Defined to 1 if GCredentials uses Linux `struct ucred`, etc.
+ */
+#undef G_CREDENTIALS_USE_LINUX_UCRED
+#undef G_CREDENTIALS_USE_FREEBSD_CMSGCRED
+#undef G_CREDENTIALS_USE_NETBSD_UNPCBID
+#undef G_CREDENTIALS_USE_OPENBSD_SOCKPEERCRED
+#undef G_CREDENTIALS_USE_SOLARIS_UCRED
+
+/*
+ * G_CREDENTIALS_NATIVE_TYPE:
+ *
+ * Defined to one of G_CREDENTIALS_TYPE_LINUX_UCRED, etc.
+ */
+#undef G_CREDENTIALS_NATIVE_TYPE
+
+/*
+ * G_CREDENTIALS_NATIVE_SIZE:
+ *
+ * Defined to the size of the %G_CREDENTIALS_NATIVE_TYPE
+ */
+#undef G_CREDENTIALS_NATIVE_SIZE
+
+/*
+ * G_CREDENTIALS_UNIX_CREDENTIALS_MESSAGE_SUPPORTED:
+ *
+ * Defined to 1 if we have a message-passing API in which credentials
+ * are attached to a particular message, such as `SCM_CREDENTIALS` on Linux
+ * or `SCM_CREDS` on FreeBSD.
+ */
+#undef G_CREDENTIALS_UNIX_CREDENTIALS_MESSAGE_SUPPORTED
+
+/*
+ * G_CREDENTIALS_SOCKET_GET_CREDENTIALS_SUPPORTED:
+ *
+ * Defined to 1 if we have a `getsockopt()`-style API in which one end of
+ * a socket connection can directly query the credentials of the process
+ * that initiated the other end, such as `getsockopt SO_PEERCRED` on Linux
+ * or `getpeereid()` on multiple operating systems.
+ */
+#undef G_CREDENTIALS_SOCKET_GET_CREDENTIALS_SUPPORTED
+
+/*
+ * G_CREDENTIALS_SPOOFING_SUPPORTED:
+ *
+ * Defined to 1 if privileged processes can spoof their credentials when
+ * using the message-passing API.
+ */
+#undef G_CREDENTIALS_SPOOFING_SUPPORTED
+
 #ifdef __linux__
 #define G_CREDENTIALS_SUPPORTED 1
 #define G_CREDENTIALS_USE_LINUX_UCRED 1
-- 
2.22.0


From 1485a97d8051b0aa047987f7b0c0bfe4ba4ce55b Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Fri, 18 Oct 2019 10:55:09 +0100
Subject: [PATCH 2/4] credentials: Invalid Linux struct ucred means "no
 information"

On Linux, if getsockopt SO_PEERCRED is used on a TCP socket, one
might expect it to fail with an appropriate error like ENOTSUP or
EPROTONOSUPPORT. However, it appears that in fact it succeeds, but
yields a credentials structure with pid 0, uid -1 and gid -1. These
are not real process, user and group IDs that can be allocated to a
real process (pid 0 needs to be reserved to give kill(0) its documented
special semantics, and similarly uid and gid -1 need to be reserved for
setresuid() and setresgid()) so it is not meaningful to signal them to
high-level API users.

An API user with Linux-specific knowledge can still inspect these fields
via g_credentials_get_native() if desired.

Similarly, if SO_PASSCRED is used to receive a SCM_CREDENTIALS message
on a receiving Unix socket, but the sending socket had not enabled
SO_PASSCRED at the time that the message was sent, it is possible
for it to succeed but yield a credentials structure with pid 0, uid
/proc/sys/kernel/overflowuid and gid /proc/sys/kernel/overflowgid. Even
if we were to read those pseudo-files, we cannot distinguish between
the overflow IDs and a real process that legitimately has the same IDs
(typically they are set to 'nobody' and 'nogroup', which can be used
by a real process), so we detect this situation by noticing that
pid == 0, and to save syscalls we do not read the overflow IDs from
/proc at all.

This results in a small API change: g_credentials_is_same_user() now
returns FALSE if we compare two credentials structures that are both
invalid. This seems like reasonable, conservative behaviour: if we cannot
prove that they are the same user, we should assume they are not.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 gio/gcredentials.c | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/gio/gcredentials.c b/gio/gcredentials.c
index c350e3c88..c4794ded7 100644
--- a/gio/gcredentials.c
+++ b/gio/gcredentials.c
@@ -265,6 +265,35 @@ g_credentials_to_string (GCredentials *credentials)
 
 /* ---------------------------------------------------------------------------------------------------- */
 
+#if G_CREDENTIALS_USE_LINUX_UCRED
+/*
+ * Check whether @native contains invalid data. If getsockopt SO_PEERCRED
+ * is used on a TCP socket, it succeeds but yields a credentials structure
+ * with pid 0, uid -1 and gid -1. Similarly, if SO_PASSCRED is used on a
+ * receiving Unix socket when the sending socket did not also enable
+ * SO_PASSCRED, it can succeed but yield a credentials structure with
+ * pid 0, uid /proc/sys/kernel/overflowuid and gid
+ * /proc/sys/kernel/overflowgid.
+ */
+static gboolean
+linux_ucred_check_valid (struct ucred  *native,
+                         GError       **error)
+{
+  if (native->pid == 0
+      || native->uid == -1
+      || native->gid == -1)
+    {
+      g_set_error_literal (error,
+                           G_IO_ERROR,
+                           G_IO_ERROR_INVALID_DATA,
+                           _("GCredentials contains invalid data"));
+      return FALSE;
+    }
+
+  return TRUE;
+}
+#endif
+
 /**
  * g_credentials_is_same_user:
  * @credentials: A #GCredentials.
@@ -294,7 +323,8 @@ g_credentials_is_same_user (GCredentials  *credentials,
 
   ret = FALSE;
 #if G_CREDENTIALS_USE_LINUX_UCRED
-  if (credentials->native.uid == other_credentials->native.uid)
+  if (linux_ucred_check_valid (&credentials->native, NULL)
+      && credentials->native.uid == other_credentials->native.uid)
     ret = TRUE;
 #elif G_CREDENTIALS_USE_FREEBSD_CMSGCRED
   if (credentials->native.cmcred_euid == other_credentials->native.cmcred_euid)
@@ -453,7 +483,10 @@ g_credentials_get_unix_user (GCredentials    *credentials,
   g_return_val_if_fail (error == NULL || *error == NULL, -1);
 
 #if G_CREDENTIALS_USE_LINUX_UCRED
-  ret = credentials->native.uid;
+  if (linux_ucred_check_valid (&credentials->native, error))
+    ret = credentials->native.uid;
+  else
+    ret = -1;
 #elif G_CREDENTIALS_USE_FREEBSD_CMSGCRED
   ret = credentials->native.cmcred_euid;
 #elif G_CREDENTIALS_USE_NETBSD_UNPCBID
@@ -499,7 +532,10 @@ g_credentials_get_unix_pid (GCredentials    *credentials,
   g_return_val_if_fail (error == NULL || *error == NULL, -1);
 
 #if G_CREDENTIALS_USE_LINUX_UCRED
-  ret = credentials->native.pid;
+  if (linux_ucred_check_valid (&credentials->native, error))
+    ret = credentials->native.pid;
+  else
+    ret = -1;
 #elif G_CREDENTIALS_USE_FREEBSD_CMSGCRED
   ret = credentials->native.cmcred_pid;
 #elif G_CREDENTIALS_USE_NETBSD_UNPCBID
-- 
2.22.0


From ee502dbbe89a5976c32eb8863c9a9d274ddb60e1 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Mon, 14 Oct 2019 08:47:39 +0100
Subject: [PATCH 3/4] GDBus: prefer getsockopt()-style credentials-passing APIs

Conceptually, a D-Bus server is really trying to determine the credentials
of (the process that initiated) a connection, not the credentials that
the process had when it sent a particular message. Ideally, it does
this with a getsockopt()-style API that queries the credentials of the
connection's initiator without requiring any particular cooperation from
that process, avoiding a class of possible failures.

The leading '\0' in the D-Bus protocol is primarily a workaround
for platforms where the message-based credentials-passing API is
strictly better than the getsockopt()-style API (for example, on
FreeBSD, SCM_CREDS includes a process ID but getpeereid() does not),
or where the getsockopt()-style API does not exist at all. As a result
libdbus, the reference implementation of D-Bus, does not implement
Linux SCM_CREDENTIALS at all - it has no reason to do so, because the
SO_PEERCRED socket option is equally informative.

This change makes GDBusServer on Linux more closely match the behaviour
of libdbus.

In particular, GNOME/glib#1831 indicates that when a libdbus client
connects to a GDBus server, recvmsg() sometimes yields a SCM_CREDENTIALS
message with cmsg_data={pid=0, uid=65534, gid=65534}. I think this is
most likely a race condition in the early steps to connect:

        client           server
    connect
                         accept
    send '\0' <- race -> set SO_PASSCRED = 1
                         receive '\0'

If the server wins the race:

        client           server
    connect
                         accept
                         set SO_PASSCRED = 1
    send '\0'
                         receive '\0'

then everything is fine. However, if the client wins the race:

        client           server
    connect
                         accept
    send '\0'
                         set SO_PASSCRED = 1
                         receive '\0'

then the kernel does not record credentials for the message containing
'\0' (because SO_PASSCRED was 0 at the time). However, by the time the
server receives the message, the kernel knows that credentials are
desired. I would have expected the kernel to omit the credentials header
in this case, but it seems that instead, it synthesizes a credentials
structure with a dummy process ID 0, a dummy uid derived from
/proc/sys/kernel/overflowuid and a dummy gid derived from
/proc/sys/kernel/overflowgid.

In an unconfigured GDBusServer, hitting this race condition results in
falling back to DBUS_COOKIE_SHA1 authentication, which in practice usually
succeeds in authenticating the peer's uid. However, we encourage AF_UNIX
servers on Unix platforms to allow only EXTERNAL authentication as a
security-hardening measure, because DBUS_COOKIE_SHA1 relies on a series
of assumptions including a cryptographically strong PRNG and a shared
home directory with no write access by others, which are not necessarily
true for all operating systems and users. EXTERNAL authentication will
fail if the server cannot determine the client's credentials.

In particular, this caused a regression when CVE-2019-14822 was fixed
in ibus, which appears to be resolved by this commit. Qt clients
(which use libdbus) intermittently fail to connect to an ibus server
(which uses GDBusServer), because ibus no longer allows DBUS_COOKIE_SHA1
authentication or non-matching uids.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Closes: https://gitlab.gnome.org/GNOME/glib/issues/1831
---
 gio/gcredentialsprivate.h | 18 ++++++++++++++++++
 gio/gdbusauth.c           | 27 +++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/gio/gcredentialsprivate.h b/gio/gcredentialsprivate.h
index 06f0aed19..e9ec09b9f 100644
--- a/gio/gcredentialsprivate.h
+++ b/gio/gcredentialsprivate.h
@@ -81,6 +81,18 @@
  */
 #undef G_CREDENTIALS_SPOOFING_SUPPORTED
 
+/*
+ * G_CREDENTIALS_PREFER_MESSAGE_PASSING:
+ *
+ * Defined to 1 if the data structure transferred by the message-passing
+ * API is strictly more informative than the one transferred by the
+ * `getsockopt()`-style API, and hence should be preferred, even for
+ * protocols like D-Bus that are defined in terms of the credentials of
+ * the (process that opened the) socket, as opposed to the credentials
+ * of an individual message.
+ */
+#undef G_CREDENTIALS_PREFER_MESSAGE_PASSING
+
 #ifdef __linux__
 #define G_CREDENTIALS_SUPPORTED 1
 #define G_CREDENTIALS_USE_LINUX_UCRED 1
@@ -100,6 +112,12 @@
 #define G_CREDENTIALS_NATIVE_SIZE (sizeof (struct cmsgcred))
 #define G_CREDENTIALS_UNIX_CREDENTIALS_MESSAGE_SUPPORTED 1
 #define G_CREDENTIALS_SPOOFING_SUPPORTED 1
+/* GLib doesn't implement it yet, but FreeBSD's getsockopt()-style API
+ * is getpeereid(), which is not as informative as struct cmsgcred -
+ * it does not tell us the PID. As a result, libdbus prefers to use
+ * SCM_CREDS, and if we implement getpeereid() in future, we should
+ * do the same. */
+#define G_CREDENTIALS_PREFER_MESSAGE_PASSING 1
 
 #elif defined(__NetBSD__)
 #define G_CREDENTIALS_SUPPORTED 1
diff --git a/gio/gdbusauth.c b/gio/gdbusauth.c
index 752ec23fc..14cc5d70e 100644
--- a/gio/gdbusauth.c
+++ b/gio/gdbusauth.c
@@ -31,6 +31,7 @@
 #include "gdbusutils.h"
 #include "gioenumtypes.h"
 #include "gcredentials.h"
+#include "gcredentialsprivate.h"
 #include "gdbusprivate.h"
 #include "giostream.h"
 #include "gdatainputstream.h"
@@ -969,9 +970,31 @@ _g_dbus_auth_run_server (GDBusAuth              *auth,
 
   g_data_input_stream_set_newline_type (dis, G_DATA_STREAM_NEWLINE_TYPE_CR_LF);
 
-  /* first read the NUL-byte */
+  /* read the NUL-byte, possibly with credentials attached */
 #ifdef G_OS_UNIX
-  if (G_IS_UNIX_CONNECTION (auth->priv->stream))
+#ifndef G_CREDENTIALS_PREFER_MESSAGE_PASSING
+  if (G_IS_SOCKET_CONNECTION (auth->priv->stream))
+    {
+      GSocket *sock = g_socket_connection_get_socket (G_SOCKET_CONNECTION (auth->priv->stream));
+
+      local_error = NULL;
+      credentials = g_socket_get_credentials (sock, &local_error);
+
+      if (credentials == NULL && !g_error_matches (local_error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED))
+        {
+          g_propagate_error (error, local_error);
+          goto out;
+        }
+      else
+        {
+          /* Clear the error indicator, so we can retry with
+           * g_unix_connection_receive_credentials() if necessary */
+          g_clear_error (&local_error);
+        }
+    }
+#endif
+
+  if (credentials == NULL && G_IS_UNIX_CONNECTION (auth->priv->stream))
     {
       local_error = NULL;
       credentials = g_unix_connection_receive_credentials (G_UNIX_CONNECTION (auth->priv->stream),
-- 
2.22.0


From 9f962ebeac1d67223579ad0d261c4c8215f7c427 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Fri, 11 Oct 2019 19:02:55 +0100
Subject: [PATCH 4/4] Add a test for GDBusServer authentication

In particular, if libbdus is available, we test interoperability with
a libdbus client: see GNOME/glib#1831. Because that issue describes a
race condition, we do each test repeatedly to try to hit the failing
case.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 gio/tests/gdbus-server-auth.c | 491 ++++++++++++++++++++++++++++++++++
 gio/tests/meson.build         |  10 +-
 2 files changed, 500 insertions(+), 1 deletion(-)
 create mode 100644 gio/tests/gdbus-server-auth.c

diff --git a/gio/tests/gdbus-server-auth.c b/gio/tests/gdbus-server-auth.c
new file mode 100644
index 000000000..6a72ba6c1
--- /dev/null
+++ b/gio/tests/gdbus-server-auth.c
@@ -0,0 +1,491 @@
+/*
+ * Copyright 2019 Collabora Ltd.
+ *
+ * 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/>.
+ */
+
+#include "config.h"
+
+#include <gio/gio.h>
+
+#ifdef HAVE_DBUS1
+#include <dbus/dbus.h>
+#endif
+
+typedef enum
+{
+  INTEROP_FLAGS_EXTERNAL = (1 << 0),
+  INTEROP_FLAGS_ANONYMOUS = (1 << 1),
+  INTEROP_FLAGS_SHA1 = (1 << 2),
+  INTEROP_FLAGS_TCP = (1 << 3),
+  INTEROP_FLAGS_LIBDBUS = (1 << 4),
+  INTEROP_FLAGS_NONE = 0
+} InteropFlags;
+
+static gboolean
+allow_external_cb (G_GNUC_UNUSED GDBusAuthObserver *observer,
+                   const char *mechanism,
+                   G_GNUC_UNUSED gpointer user_data)
+{
+  if (g_strcmp0 (mechanism, "EXTERNAL") == 0)
+    {
+      g_debug ("Accepting EXTERNAL authentication");
+      return TRUE;
+    }
+  else
+    {
+      g_debug ("Rejecting \"%s\" authentication: not EXTERNAL", mechanism);
+      return FALSE;
+    }
+}
+
+static gboolean
+allow_anonymous_cb (G_GNUC_UNUSED GDBusAuthObserver *observer,
+                    const char *mechanism,
+                    G_GNUC_UNUSED gpointer user_data)
+{
+  if (g_strcmp0 (mechanism, "ANONYMOUS") == 0)
+    {
+      g_debug ("Accepting ANONYMOUS authentication");
+      return TRUE;
+    }
+  else
+    {
+      g_debug ("Rejecting \"%s\" authentication: not ANONYMOUS", mechanism);
+      return FALSE;
+    }
+}
+
+static gboolean
+allow_sha1_cb (G_GNUC_UNUSED GDBusAuthObserver *observer,
+               const char *mechanism,
+               G_GNUC_UNUSED gpointer user_data)
+{
+  if (g_strcmp0 (mechanism, "DBUS_COOKIE_SHA1") == 0)
+    {
+      g_debug ("Accepting DBUS_COOKIE_SHA1 authentication");
+      return TRUE;
+    }
+  else
+    {
+      g_debug ("Rejecting \"%s\" authentication: not DBUS_COOKIE_SHA1",
+               mechanism);
+      return FALSE;
+    }
+}
+
+static gboolean
+allow_any_mechanism_cb (G_GNUC_UNUSED GDBusAuthObserver *observer,
+                        const char *mechanism,
+                        G_GNUC_UNUSED gpointer user_data)
+{
+  g_debug ("Accepting \"%s\" authentication", mechanism);
+  return TRUE;
+}
+
+static gboolean
+authorize_any_authenticated_peer_cb (G_GNUC_UNUSED GDBusAuthObserver *observer,
+                                     G_GNUC_UNUSED GIOStream *stream,
+                                     GCredentials *credentials,
+                                     G_GNUC_UNUSED gpointer user_data)
+{
+  if (credentials == NULL)
+    {
+      g_debug ("Authorizing peer with no credentials");
+    }
+  else
+    {
+      gchar *str = g_credentials_to_string (credentials);
+
+      g_debug ("Authorizing peer with credentials: %s", str);
+      g_free (str);
+    }
+
+  return TRUE;
+}
+
+static GDBusMessage *
+whoami_filter_cb (GDBusConnection *connection,
+                  GDBusMessage *message,
+                  gboolean incoming,
+                  G_GNUC_UNUSED gpointer user_data)
+{
+  if (!incoming)
+    return message;
+
+  if (g_dbus_message_get_message_type (message) == G_DBUS_MESSAGE_TYPE_METHOD_CALL &&
+      g_strcmp0 (g_dbus_message_get_member (message), "WhoAmI") == 0)
+    {
+      GDBusMessage *reply = g_dbus_message_new_method_reply (message);
+      gint64 uid = -1;
+      gint64 pid = -1;
+#ifdef G_OS_UNIX
+      GCredentials *credentials = g_dbus_connection_get_peer_credentials (connection);
+
+      if (credentials != NULL)
+        {
+          uid = (gint64) g_credentials_get_unix_user (credentials, NULL);
+          pid = (gint64) g_credentials_get_unix_pid (credentials, NULL);
+        }
+#endif
+
+      g_dbus_message_set_body (reply,
+                               g_variant_new ("(xx)", uid, pid));
+      g_dbus_connection_send_message (connection, reply,
+                                      G_DBUS_SEND_MESSAGE_FLAGS_NONE,
+                                      NULL, NULL);
+
+      /* handled */
+      g_object_unref (message);
+      return NULL;
+    }
+
+  return message;
+}
+
+static gboolean
+new_connection_cb (G_GNUC_UNUSED GDBusServer *server,
+                   GDBusConnection *connection,
+                   G_GNUC_UNUSED gpointer user_data)
+{
+  GCredentials *credentials = g_dbus_connection_get_peer_credentials (connection);
+
+  if (credentials == NULL)
+    {
+      g_debug ("New connection from peer with no credentials");
+    }
+  else
+    {
+      gchar *str = g_credentials_to_string (credentials);
+
+      g_debug ("New connection from peer with credentials: %s", str);
+      g_free (str);
+    }
+
+  g_object_ref (connection);
+  g_dbus_connection_add_filter (connection, whoami_filter_cb, NULL, NULL);
+  return TRUE;
+}
+
+#ifdef HAVE_DBUS1
+typedef struct
+{
+  DBusError error;
+  DBusConnection *conn;
+  DBusMessage *call;
+  DBusMessage *reply;
+} LibdbusCall;
+
+static void
+libdbus_call_task_cb (GTask *task,
+                      G_GNUC_UNUSED gpointer source_object,
+                      gpointer task_data,
+                      G_GNUC_UNUSED GCancellable *cancellable)
+{
+  LibdbusCall *libdbus_call = task_data;
+
+  libdbus_call->reply = dbus_connection_send_with_reply_and_block (libdbus_call->conn,
+                                                                   libdbus_call->call,
+                                                                   -1,
+                                                                   &libdbus_call->error);
+}
+#endif /* HAVE_DBUS1 */
+
+static void
+store_result_cb (G_GNUC_UNUSED GObject *source_object,
+                 GAsyncResult *res,
+                 gpointer user_data)
+{
+  GAsyncResult **result = user_data;
+
+  g_assert_nonnull (result);
+  g_assert_null (*result);
+  *result = g_object_ref (res);
+}
+
+static void
+assert_expected_uid_pid (InteropFlags flags,
+                         gint64 uid,
+                         gint64 pid)
+{
+#ifdef G_OS_UNIX
+  if (flags & (INTEROP_FLAGS_ANONYMOUS | INTEROP_FLAGS_SHA1 | INTEROP_FLAGS_TCP))
+    {
+      /* No assertion. There is no guarantee whether credentials will be
+       * passed even though we didn't send them. Conversely, if
+       * credentials were not passed,
+       * g_dbus_connection_get_peer_credentials() always returns the
+       * credentials of the socket, and not the uid that a
+       * client might have proved it has by using DBUS_COOKIE_SHA1. */
+    }
+  else    /* We should prefer EXTERNAL whenever it is allowed. */
+    {
+#ifdef __linux__
+      /* We know that both GDBus and libdbus support full credentials-passing
+       * on Linux. */
+      g_assert_cmpint (uid, ==, getuid ());
+      g_assert_cmpint (pid, ==, getpid ());
+#else
+      g_test_message ("Please open a merge request to add appropriate "
+                      "assertions for your platform");
+#endif
+    }
+#endif /* G_OS_UNIX */
+}
+
+static void
+do_test_server_auth (const char *listenable_address,
+                     InteropFlags flags)
+{
+  GError *error = NULL;
+  GDBusServer *server;
+  GDBusAuthObserver *observer;
+  GDBusServerFlags server_flags = G_DBUS_SERVER_FLAGS_RUN_IN_THREAD;
+  gchar *guid;
+  const char *connectable_address;
+  GDBusConnection *client;
+  GAsyncResult *result = NULL;
+  GVariant *tuple;
+  gint64 uid, pid;
+#ifdef HAVE_DBUS1
+  /* GNOME/glib#1831 seems to involve a race condition, so try a few times
+   * to see if we can trigger it. */
+  gsize i;
+  gsize n = 20;
+#endif
+
+  if (g_str_has_prefix (listenable_address, "tcp:") ||
+      g_str_has_prefix (listenable_address, "nonce-tcp:"))
+    g_assert_cmpint (flags & INTEROP_FLAGS_TCP, !=, 0);
+  else
+    g_assert_cmpint (flags & INTEROP_FLAGS_TCP, ==, 0);
+
+  g_test_message ("Testing GDBus server at %s / libdbus client, with flags: "
+                  "external:%s "
+                  "anonymous:%s "
+                  "sha1:%s "
+                  "tcp:%s",
+                  listenable_address,
+                  (flags & INTEROP_FLAGS_EXTERNAL) ? "true" : "false",
+                  (flags & INTEROP_FLAGS_ANONYMOUS) ? "true" : "false",
+                  (flags & INTEROP_FLAGS_SHA1) ? "true" : "false",
+                  (flags & INTEROP_FLAGS_TCP) ? "true" : "false");
+
+#ifndef G_OS_UNIX
+  if (g_str_has_prefix (listenable_address, "unix:"))
+    {
+      g_test_skip ("unix: addresses only work on Unix");
+      return;
+    }
+#endif
+
+#if !defined(G_CREDENTIALS_UNIX_CREDENTIALS_MESSAGE_SUPPORTED) \
+  && !defined(G_CREDENTIALS_SOCKET_GET_CREDENTIALS_SUPPORTED)
+  if (flags & INTEROP_FLAGS_EXTERNAL)
+    {
+      g_test_skip ("EXTERNAL authentication not implemented on this platform");
+      return;
+    }
+#endif
+
+  if (flags & INTEROP_FLAGS_ANONYMOUS)
+    server_flags |= G_DBUS_SERVER_FLAGS_AUTHENTICATION_ALLOW_ANONYMOUS;
+
+  observer = g_dbus_auth_observer_new ();
+
+  if (flags & INTEROP_FLAGS_EXTERNAL)
+    g_signal_connect (observer, "allow-mechanism",
+                      G_CALLBACK (allow_external_cb), NULL);
+  else if (flags & INTEROP_FLAGS_ANONYMOUS)
+    g_signal_connect (observer, "allow-mechanism",
+                      G_CALLBACK (allow_anonymous_cb), NULL);
+  else if (flags & INTEROP_FLAGS_SHA1)
+    g_signal_connect (observer, "allow-mechanism",
+                      G_CALLBACK (allow_sha1_cb), NULL);
+  else
+    g_signal_connect (observer, "allow-mechanism",
+                      G_CALLBACK (allow_any_mechanism_cb), NULL);
+
+  g_signal_connect (observer, "authorize-authenticated-peer",
+                    G_CALLBACK (authorize_any_authenticated_peer_cb),
+                    NULL);
+
+  guid = g_dbus_generate_guid ();
+  server = g_dbus_server_new_sync (listenable_address,
+                                   server_flags,
+                                   guid,
+                                   observer,
+                                   NULL,
+                                   &error);
+  g_assert_no_error (error);
+  g_assert_nonnull (server);
+  g_signal_connect (server, "new-connection", G_CALLBACK (new_connection_cb), NULL);
+  g_dbus_server_start (server);
+  connectable_address = g_dbus_server_get_client_address (server);
+
+  result = NULL;
+  g_dbus_connection_new_for_address (connectable_address,
+                                     G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_CLIENT,
+                                     NULL, NULL, store_result_cb, &result);
+
+  while (result == NULL)
+    g_main_context_iteration (NULL, TRUE);
+
+  client = g_dbus_connection_new_for_address_finish (result, &error);
+  g_assert_no_error (error);
+  g_assert_nonnull (client);
+  g_clear_object (&result);
+
+  g_dbus_connection_call (client, NULL, "/", "com.example.Test", "WhoAmI",
+                          NULL, G_VARIANT_TYPE ("(xx)"),
+                          G_DBUS_CALL_FLAGS_NONE, -1, NULL, store_result_cb,
+                          &result);
+
+  while (result == NULL)
+    g_main_context_iteration (NULL, TRUE);
+
+  tuple = g_dbus_connection_call_finish (client, result, &error);
+  g_assert_no_error (error);
+  g_assert_nonnull (tuple);
+  g_clear_object (&result);
+  g_clear_object (&client);
+
+  uid = -2;
+  pid = -2;
+  g_variant_get (tuple, "(xx)", &uid, &pid);
+
+  g_debug ("Server says GDBus client is uid %" G_GINT64_FORMAT ", pid %" G_GINT64_FORMAT,
+           uid, pid);
+
+  assert_expected_uid_pid (flags, uid, pid);
+
+  g_clear_pointer (&tuple, g_variant_unref);
+
+#ifdef HAVE_DBUS1
+  for (i = 0; i < n; i++)
+    {
+      LibdbusCall libdbus_call = { DBUS_ERROR_INIT, NULL, NULL, NULL };
+      GTask *task;
+
+      libdbus_call.conn = dbus_connection_open_private (connectable_address,
+                                                        &libdbus_call.error);
+      g_assert_cmpstr (libdbus_call.error.name, ==, NULL);
+      g_assert_nonnull (libdbus_call.conn);
+
+      libdbus_call.call = dbus_message_new_method_call (NULL, "/",
+                                                        "com.example.Test",
+                                                        "WhoAmI");
+
+      if (libdbus_call.call == NULL)
+        g_error ("Out of memory");
+
+      result = NULL;
+      task = g_task_new (NULL, NULL, store_result_cb, &result);
+      g_task_set_task_data (task, &libdbus_call, NULL);
+      g_task_run_in_thread (task, libdbus_call_task_cb);
+
+      while (result == NULL)
+        g_main_context_iteration (NULL, TRUE);
+
+      g_clear_object (&result);
+
+      g_assert_cmpstr (libdbus_call.error.name, ==, NULL);
+      g_assert_nonnull (libdbus_call.reply);
+
+      uid = -2;
+      pid = -2;
+      dbus_message_get_args (libdbus_call.reply, &libdbus_call.error,
+                             DBUS_TYPE_INT64, &uid,
+                             DBUS_TYPE_INT64, &pid,
+                             DBUS_TYPE_INVALID);
+      g_assert_cmpstr (libdbus_call.error.name, ==, NULL);
+
+      g_debug ("Server says libdbus client %" G_GSIZE_FORMAT " is uid %" G_GINT64_FORMAT ", pid %" G_GINT64_FORMAT,
+               i, uid, pid);
+      assert_expected_uid_pid (flags | INTEROP_FLAGS_LIBDBUS, uid, pid);
+
+      dbus_connection_close (libdbus_call.conn);
+      dbus_connection_unref (libdbus_call.conn);
+      dbus_message_unref (libdbus_call.call);
+      dbus_message_unref (libdbus_call.reply);
+      g_clear_object (&task);
+    }
+#else /* !HAVE_DBUS1 */
+  g_test_skip ("Testing interop with libdbus not supported");
+#endif /* !HAVE_DBUS1 */
+
+  g_dbus_server_stop (server);
+  g_clear_object (&server);
+  g_clear_object (&observer);
+  g_free (guid);
+}
+
+static void
+test_server_auth (void)
+{
+  do_test_server_auth ("unix:tmpdir=/tmp/gdbus-test", INTEROP_FLAGS_NONE);
+}
+
+static void
+test_server_auth_tcp (void)
+{
+  do_test_server_auth ("tcp:host=127.0.0.1", INTEROP_FLAGS_TCP);
+}
+
+static void
+test_server_auth_anonymous (void)
+{
+  do_test_server_auth ("unix:tmpdir=/tmp/gdbus-test", INTEROP_FLAGS_ANONYMOUS);
+}
+
+static void
+test_server_auth_anonymous_tcp (void)
+{
+  do_test_server_auth ("tcp:host=127.0.0.1", INTEROP_FLAGS_ANONYMOUS | INTEROP_FLAGS_TCP);
+}
+
+static void
+test_server_auth_external (void)
+{
+  do_test_server_auth ("unix:tmpdir=/tmp/gdbus-test", INTEROP_FLAGS_EXTERNAL);
+}
+
+static void
+test_server_auth_sha1 (void)
+{
+  do_test_server_auth ("unix:tmpdir=/tmp/gdbus-test", INTEROP_FLAGS_SHA1);
+}
+
+static void
+test_server_auth_sha1_tcp (void)
+{
+  do_test_server_auth ("tcp:host=127.0.0.1", INTEROP_FLAGS_SHA1 | INTEROP_FLAGS_TCP);
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/gdbus/server-auth", test_server_auth);
+  g_test_add_func ("/gdbus/server-auth/tcp", test_server_auth_tcp);
+  g_test_add_func ("/gdbus/server-auth/anonymous", test_server_auth_anonymous);
+  g_test_add_func ("/gdbus/server-auth/anonymous/tcp", test_server_auth_anonymous_tcp);
+  g_test_add_func ("/gdbus/server-auth/external", test_server_auth_external);
+  g_test_add_func ("/gdbus/server-auth/sha1", test_server_auth_sha1);
+  g_test_add_func ("/gdbus/server-auth/sha1/tcp", test_server_auth_sha1_tcp);
+
+  return g_test_run();
+}
diff --git a/gio/tests/meson.build b/gio/tests/meson.build
index b5593a4ec..8ad02f5c0 100644
--- a/gio/tests/meson.build
+++ b/gio/tests/meson.build
@@ -115,7 +115,15 @@ if dbus1_dep.found()
     'gdbus-serialization' : {
       'extra_sources' : ['gdbus-tests.c'],
       'dependencies' : [dbus1_dep],
-    }
+    },
+    'gdbus-server-auth' : {
+      'dependencies' : [dbus1_dep],
+    },
+  }
+else
+  # We can build a cut-down version of this test without libdbus
+  gio_tests += {
+    'gdbus-server-auth' : {},
   }
 endif
 
-- 
2.22.0