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gdbus: Never buffer reads during server authentication

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Otherwise, the content of the buffer is thrown away when switching
from reading via a GDataInputStream to unbuffered reads when waiting
for the "BEGIN" line.

(The code already tried to protect against over-reading like this by
using unbuffered reads for the last few lines of the auth protocol,
but it might already be too late at that point.  The buffer of the
GDataInputStream might already contain the "BEGIN" line for example.)

This matters when connecting a sd-bus client directly to a GDBus
client.  A sd-bus client optimistically sends the whole auth
conversation in one go without waiting for intermediate replies.  This
is done to improve performance for the many short-lived connections
that are typically made.
This commit is contained in:
Marius Vollmer 2023-02-13 14:12:52 +02:00 committed by Philip Withnall
parent c83fd0bce7
commit 8f02681f6e
1 changed files with 32 additions and 20 deletions
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52
gio/gdbusauth.c
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@ -949,7 +949,6 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
{
gboolean ret;
ServerState state;
GDataInputStream *dis;
GDataOutputStream *dos;
GError *local_error;
gchar *line;
@ -965,7 +964,6 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
_g_dbus_auth_add_mechs (auth, observer);
ret = FALSE;
dis = NULL;
dos = NULL;
mech = NULL;
negotiated_capabilities = 0;
@ -981,12 +979,17 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
goto out;
}
dis = G_DATA_INPUT_STREAM (g_data_input_stream_new (g_io_stream_get_input_stream (auth->priv->stream)));
dos = G_DATA_OUTPUT_STREAM (g_data_output_stream_new (g_io_stream_get_output_stream (auth->priv->stream)));
g_filter_input_stream_set_close_base_stream (G_FILTER_INPUT_STREAM (dis), FALSE);
g_filter_output_stream_set_close_base_stream (G_FILTER_OUTPUT_STREAM (dos), FALSE);
/* We use an extremely slow (but reliable) line reader for input
* instead of something buffered - this basically does a recvfrom()
* system call per character
*
* (the problem with using GDataInputStream's read_line is that
* because of buffering it might start reading into the first D-Bus
* message that appears after "BEGIN\r\n"....)
*/
g_data_input_stream_set_newline_type (dis, G_DATA_STREAM_NEWLINE_TYPE_CR_LF);
dos = G_DATA_OUTPUT_STREAM (g_data_output_stream_new (g_io_stream_get_output_stream (auth->priv->stream)));
g_filter_output_stream_set_close_base_stream (G_FILTER_OUTPUT_STREAM (dos), FALSE);
/* read the NUL-byte, possibly with credentials attached */
#ifndef G_CREDENTIALS_PREFER_MESSAGE_PASSING
@ -1026,11 +1029,22 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
}
else
{
gchar c;
gssize num_read;
local_error = NULL;
(void)g_data_input_stream_read_byte (dis, cancellable, &local_error);
if (local_error != NULL)
num_read = g_input_stream_read (g_io_stream_get_input_stream (auth->priv->stream),
&c, 1,
cancellable, &local_error);
if (num_read != 1 || local_error != NULL)
{
g_propagate_error (error, local_error);
if (local_error == NULL)
g_set_error_literal (error,
G_IO_ERROR,
G_IO_ERROR_FAILED,
_ ("Unexpected lack of content trying to read a byte"));
else
g_propagate_error (error, local_error);
goto out;
}
}
@ -1058,7 +1072,10 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
{
case SERVER_STATE_WAITING_FOR_AUTH:
debug_print ("SERVER: WaitingForAuth");
line = _my_g_data_input_stream_read_line (dis, &line_length, cancellable, error);
line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
&line_length,
cancellable,
error);
debug_print ("SERVER: WaitingForAuth, read '%s'", line);
if (line == NULL)
goto out;
@ -1276,7 +1293,10 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
case SERVER_STATE_WAITING_FOR_DATA:
debug_print ("SERVER: WaitingForData");
line = _my_g_data_input_stream_read_line (dis, &line_length, cancellable, error);
line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
&line_length,
cancellable,
error);
debug_print ("SERVER: WaitingForData, read '%s'", line);
if (line == NULL)
goto out;
@ -1315,13 +1335,6 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
case SERVER_STATE_WAITING_FOR_BEGIN:
debug_print ("SERVER: WaitingForBegin");
/* Use extremely slow (but reliable) line reader - this basically
* does a recvfrom() system call per character
*
* (the problem with using GDataInputStream's read_line is that because of
* buffering it might start reading into the first D-Bus message that
* appears after "BEGIN\r\n"....)
*/
line = _my_g_input_stream_read_line_safe (g_io_stream_get_input_stream (auth->priv->stream),
&line_length,
cancellable,
@ -1380,7 +1393,6 @@ _g_dbus_auth_run_server (GDBusAuth *auth,
out:
g_clear_object (&mech);
g_clear_object (&dis);
g_clear_object (&dos);
g_clear_object (&own_credentials);