264 lines
10 KiB
Diff
264 lines
10 KiB
Diff
From 327681e682af8c413fc26a9bd3cba4e77be3a069 Mon Sep 17 00:00:00 2001
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From: Philip Withnall <pwithnall@gnome.org>
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Date: Sat, 4 Jul 2026 18:13:08 +0100
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Subject: [PATCH] gdbusauth: Limit length of lines read from client
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The client isn’t trusted at this point, and there was previously nothing
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limiting how long a line `GDBusAuth` would read. So an untrusted client
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could exhaust the server’s memory by sending anything except `\r\n`.
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Fix that by applying a reasonably length limit when reading a line, and
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add a unit test.
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Spotted by Gitee Codepecker Lab.
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Signed-off-by: Philip Withnall <pwithnall@gnome.org>
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Fixes: #3985
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---
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gio/gdbusauth.c | 44 +++++++++++++++
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gio/tests/gdbus-auth.c | 119 +++++++++++++++++++++++++++++++++++++++++
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2 files changed, 163 insertions(+)
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diff --git a/gio/gdbusauth.c b/gio/gdbusauth.c
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index 9e31c8318..a5938c969 100644
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--- a/gio/gdbusauth.c
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+++ b/gio/gdbusauth.c
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@@ -260,6 +260,21 @@ find_mech_by_name (GDBusAuth *auth,
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return ret;
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}
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+static size_t
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+get_longest_mechanism_name_length (GDBusAuth *auth)
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+{
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+ size_t len = 0;
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+
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+ for (GList *l = auth->priv->available_mechanisms; l != NULL; l = l->next)
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+ {
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+ Mechanism *m = l->data;
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+
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+ len = MAX (len, strlen (m->name));
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+ }
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+
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+ return len;
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+}
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+
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GDBusAuth *
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_g_dbus_auth_new (GIOStream *stream)
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{
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@@ -268,6 +283,20 @@ _g_dbus_auth_new (GIOStream *stream)
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NULL);
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}
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+/* Arbitrarily chosen limit on the length of a DATA command payload, to prevent
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+ * unbounded reads from malicious clients.
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+ *
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+ * - The ANONYMOUS mechanism doesn’t use DATA.
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+ * - The EXTERNAL mechanism just uses it to transfer a decimal-encoded UID.
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+ * - The DBUS_COOKIE_SHA1 mechanism transfers a challenge and a SHA1 hash. The
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+ * hash is bounded in length, but the challenge is not, so could potentially
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+ * hit this limit. It doesn’t seem unreasonable to bound the challenge to
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+ * ~4KB though. GDBus itself generates a 16 byte challenge.
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+ *
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+ * See https://dbus.freedesktop.org/doc/dbus-specification.html#auth-command-data
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+ */
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+#define MAX_DATA_PAYLOAD_LENGTH_BYTES 4096
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+
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/* ---------------------------------------------------------------------------------------------------- */
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/* like g_data_input_stream_read_line() but sets error if there's no content to read */
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static gchar *
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@@ -305,6 +334,7 @@ _my_g_data_input_stream_read_line (GDataInputStream *dis,
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*/
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static gchar *
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_my_g_input_stream_read_line_safe (GInputStream *i,
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+ size_t max_line_length,
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gsize *out_line_length,
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GCancellable *cancellable,
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GError **error)
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@@ -314,11 +344,22 @@ _my_g_input_stream_read_line_safe (GInputStream *i,
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gssize num_read;
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gboolean last_was_cr;
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+ g_assert (max_line_length <= SIZE_MAX - 2);
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+
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str = g_string_new (NULL);
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last_was_cr = FALSE;
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while (TRUE)
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{
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+ if (str->len >= max_line_length + 2 /* allow for \r\n */)
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+ {
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+ g_set_error_literal (error,
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+ G_IO_ERROR,
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+ G_IO_ERROR_FAILED,
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+ _("Malformed D-Bus authentication line"));
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+ goto fail;
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+ }
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+
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num_read = g_input_stream_read (i,
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&c,
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1,
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@@ -1071,6 +1112,7 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
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case SERVER_STATE_WAITING_FOR_AUTH:
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debug_print ("SERVER: WaitingForAuth");
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line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
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+ strlen ("AUTH ") + get_longest_mechanism_name_length (auth) + strlen (" ") + MAX_DATA_PAYLOAD_LENGTH_BYTES,
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&line_length,
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cancellable,
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error);
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@@ -1292,6 +1334,7 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
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case SERVER_STATE_WAITING_FOR_DATA:
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debug_print ("SERVER: WaitingForData");
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line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
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+ strlen ("DATA ") + MAX_DATA_PAYLOAD_LENGTH_BYTES,
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&line_length,
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cancellable,
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error);
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@@ -1334,6 +1377,7 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
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case SERVER_STATE_WAITING_FOR_BEGIN:
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debug_print ("SERVER: WaitingForBegin");
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line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
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+ MAX (strlen ("BEGIN"), strlen ("NEGOTIATE_UNIX_FD")),
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&line_length,
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cancellable,
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error);
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diff --git a/gio/tests/gdbus-auth.c b/gio/tests/gdbus-auth.c
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index 657571be3..3323d6eeb 100644
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--- a/gio/tests/gdbus-auth.c
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+++ b/gio/tests/gdbus-auth.c
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@@ -263,6 +263,124 @@ temp_dbus_keyrings_teardown (void)
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g_unsetenv ("G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION");
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}
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+static void
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+async_result_cb (GObject *obj,
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+ GAsyncResult *result,
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+ void *user_data)
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+{
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+ GAsyncResult **result_out = user_data;
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+
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+ g_assert (result_out != NULL);
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+ g_assert (*result_out == NULL);
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+
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+ *result_out = g_object_ref (result);
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+ g_main_context_wakeup (g_main_context_get_thread_default ());
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+}
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+
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+static gboolean
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+server_new_connection_unexpected_cb (GDBusServer *server,
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+ GDBusConnection *connection,
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+ void *user_data)
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+{
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+ g_assert_not_reached ();
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+ return FALSE;
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+}
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+
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+static void
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+test_auth_server_read_limit (void)
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+{
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+ GDBusServer *server = NULL;
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+ unsigned long new_connection_id = 0;
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+ const char *server_address;
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+ GIOStream *client_stream = NULL;
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+ GOutputStream *client_output_stream;
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+ GInputStream *client_input_stream;
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+ GAsyncResult *result = NULL;
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+ char *write_buffer = NULL;
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+ char read_buffer[100];
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+ ssize_t read_len;
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+ size_t bytes_written;
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+ GError *local_error = NULL;
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+
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+ g_test_summary ("Test that GDBusServer limits the lengths of reads it does during auth from a client");
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+ g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/3985");
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+
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+ server = server_new_for_mechanism (NULL);
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+
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+ new_connection_id = g_signal_connect (server,
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+ "new-connection",
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+ G_CALLBACK (server_new_connection_unexpected_cb),
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+ NULL);
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+ server_address = g_dbus_server_get_client_address (server);
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+ g_dbus_server_start (server);
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+
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+ /* Start connecting as a client */
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+ g_dbus_address_get_stream (server_address, NULL, async_result_cb, &result);
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+
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+ while (result == NULL)
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+ g_main_context_iteration (NULL, TRUE);
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+
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+ client_stream = g_dbus_address_get_stream_finish (result, NULL, &local_error);
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+ g_assert_no_error (local_error);
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+ g_clear_object (&result);
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+
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+ /* Send an over-long AUTH line, maliciously */
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+ client_output_stream = g_io_stream_get_output_stream (client_stream);
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+ client_input_stream = g_io_stream_get_input_stream (client_stream);
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+
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+ write_buffer = g_strdup_printf ("AUTH DBUS_COOKIE_SHA1 context%0*d 123 456\r\n", 5000, 0);
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+
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+ g_output_stream_write_all_async (client_output_stream,
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+ write_buffer,
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+ strlen (write_buffer),
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+ G_PRIORITY_DEFAULT,
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+ NULL,
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+ async_result_cb,
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+ &result);
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+
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+ while (result == NULL)
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+ g_main_context_iteration (NULL, TRUE);
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+
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+ g_output_stream_write_all_finish (client_output_stream, result, &bytes_written, &local_error);
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+ g_assert_no_error (local_error);
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+ g_assert_cmpuint (bytes_written, ==, strlen (write_buffer));
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+ g_clear_object (&result);
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+
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+ g_clear_pointer (&write_buffer, g_free);
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+
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+ /* Authentication should have been rejected, so reading or writing the stream
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+ * should now fail. */
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+ read_len = g_input_stream_read (client_input_stream,
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+ read_buffer,
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+ sizeof (read_buffer),
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+ NULL,
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+ &local_error);
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+ g_assert_error (local_error, G_IO_ERROR, G_IO_ERROR_CONNECTION_CLOSED);
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+ g_assert_cmpint (read_len, <, 0);
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+ g_clear_error (&local_error);
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+
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+ write_buffer = g_strdup_printf ("AUTH\r\n");
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+
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+ g_output_stream_write_all (client_output_stream,
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+ write_buffer,
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+ strlen (write_buffer),
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+ &bytes_written,
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+ NULL,
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+ &local_error);
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+ g_assert_error (local_error, G_IO_ERROR, G_IO_ERROR_CONNECTION_CLOSED);
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+ g_assert_cmpuint (bytes_written, ==, 0);
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+ g_clear_error (&local_error);
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+
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+ g_clear_pointer (&write_buffer, g_free);
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+
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+ /* Cleanup */
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+ g_clear_object (&client_stream);
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+ g_dbus_server_stop (server);
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+
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+ g_clear_signal_handler (&new_connection_id, server);
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+ g_clear_object (&server);
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+}
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+
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/* ---------------------------------------------------------------------------------------------------- */
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int
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@@ -282,6 +400,7 @@ main (int argc,
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g_test_add_func ("/gdbus/auth/server/ANONYMOUS", auth_server_anonymous);
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g_test_add_func ("/gdbus/auth/server/EXTERNAL", auth_server_external);
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g_test_add_func ("/gdbus/auth/server/DBUS_COOKIE_SHA1", auth_server_dbus_cookie_sha1);
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+ g_test_add_func ("/gdbus/auth/server/read-limit", test_auth_server_read_limit);
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/* TODO: we currently don't have tests for
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*
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