From f68021fcd63094f1151f22fc62cca202e43159bb Mon Sep 17 00:00:00 2001
From: Ralf Habacker <ralf.habacker@freenet.de>
Date: Sat, 20 Aug 2016 01:07:12 +0200
Subject: [PATCH] On bus startup check given auth in config file against
 supported mechanismen.

With recent code starting dbus-daemon with an unsupported auth mechanism
let dbus-daemon silently ignore this issue. Clients connecting to this
server fails to connect without any descriptive explanation of the
root cause, only the message 'Rejected client connection due to lack
of memory' error is reported in dbus-daemon verbose log, which is disabled
in production environments.

With this patch dbus-daemon checks the supported auth mechanisms on startup
and shuts down with a descriptive error message, which gives admin an
immediate feedback on service startup/restart.

The proposal to perform this check in _dbus_auth_set_mechanisms() has the
drawback that the check would not be performed on bus startup, only at
client side and on handling client connections at server side.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=96577
Signed-off-by: Ralf Habacker <ralf.habacker@freenet.de>
---
 bus/bus.c        | 21 +++++++++++++++++++++
 dbus/dbus-auth.c | 41 +++++++++++++++++++++++++++++++++++++++++
 dbus/dbus-auth.h |  4 ++++
 3 files changed, 66 insertions(+)

diff --git a/bus/bus.c b/bus/bus.c
index 103447c..90d54d2 100644
--- a/bus/bus.c
+++ b/bus/bus.c
@@ -37,6 +37,7 @@
 #include "apparmor.h"
 #include "audit.h"
 #include "dir-watch.h"
+#include <dbus/dbus-auth.h>
 #include <dbus/dbus-list.h>
 #include <dbus/dbus-hash.h>
 #include <dbus/dbus-credentials.h>
@@ -408,6 +409,26 @@ process_config_first_time_only (BusContext       *context,
       link = _dbus_list_get_first_link (auth_mechanisms_list);
       while (link != NULL)
         {
+          DBusString name;
+          _dbus_string_init_const (&name, link->data);
+          if (!_dbus_auth_is_supported_mechanism (&name))
+            {
+              DBusString list;
+              if (!_dbus_string_init (&list))
+                goto oom;
+
+              if (!_dbus_auth_dump_supported_mechanisms (&list))
+                {
+                  _dbus_string_free (&list);
+                  goto oom;
+                }
+              dbus_set_error (error, DBUS_ERROR_FAILED,
+                              "Unsupported auth mechanism \"%s\" in bus config file detected. Supported mechanisms are \"%s\".",
+                              link->data,
+                              _dbus_string_get_const_data (&list));
+              _dbus_string_free (&list);
+              goto failed;
+            }
           auth_mechanisms[i] = _dbus_strdup (link->data);
           if (auth_mechanisms[i] == NULL)
             goto oom;
diff --git a/dbus/dbus-auth.c b/dbus/dbus-auth.c
index 18c12b4..a7cf9e1 100644
--- a/dbus/dbus-auth.c
+++ b/dbus/dbus-auth.c
@@ -3002,6 +3002,47 @@ _dbus_auth_get_unix_fd_negotiated(DBusAuth *auth)
   return auth->unix_fd_negotiated;
 }
 
+/**
+ * Queries whether the given auth mechanism is supported.
+ *
+ * @param auth the auth mechanism to query for
+ * @returns #TRUE when auth mechanism is supported
+ */
+dbus_bool_t
+_dbus_auth_is_supported_mechanism (DBusString *name)
+{
+  _dbus_assert (name != NULL);
+
+  return find_mech(name, NULL) != 0;
+}
+
+/**
+ * Return string containing all supported auth mechanisms.
+ *
+ * @param string to hold the supported auth mechanisms
+ * @returns #FALSE on oom
+ */
+dbus_bool_t
+_dbus_auth_dump_supported_mechanisms (DBusString *buffer)
+{
+  int i;
+  _dbus_assert (buffer != NULL);
+
+  i = 0;
+  while (all_mechanisms[i].mechanism != NULL)
+    {
+      if (i > 0)
+        {
+          if (!_dbus_string_append (buffer, ","))
+            return FALSE;
+        }
+      if (!_dbus_string_append (buffer, all_mechanisms[i].mechanism))
+        return FALSE;
+      ++i;
+    }
+  return TRUE;
+}
+
 /** @} */
 
 /* tests in dbus-auth-util.c */
diff --git a/dbus/dbus-auth.h b/dbus/dbus-auth.h
index c62bcd1..991daca 100644
--- a/dbus/dbus-auth.h
+++ b/dbus/dbus-auth.h
@@ -92,6 +92,10 @@ const char*   _dbus_auth_get_guid_from_server(DBusAuth               *auth);
 
 void          _dbus_auth_set_unix_fd_possible(DBusAuth               *auth, dbus_bool_t b);
 dbus_bool_t   _dbus_auth_get_unix_fd_negotiated(DBusAuth             *auth);
+DBUS_PRIVATE_EXPORT
+dbus_bool_t   _dbus_auth_is_supported_mechanism(DBusString         *name);
+DBUS_PRIVATE_EXPORT
+dbus_bool_t   _dbus_auth_dump_supported_mechanisms(DBusString        *buffer);
 
 DBUS_END_DECLS
 
-- 
2.6.6