Fail to generate random bytes instead of falling back to rand()

This is more robust against broken setups where we run out
of memory or cannot read /dev/urandom.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=90414
Reviewed-by: Ralf Habacker <ralf.habacker@freenet.de>
[smcv: document @error]
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

1 files changed, 46 insertions, 18 deletions

diff --git a/dbus/dbus-auth.c b/dbus/dbus-auth.c
index 1503d5f1..f2227875 100644
--- a/dbus/dbus-auth.c
+++ b/dbus/dbus-auth.c
@@ -524,10 +524,8 @@ sha1_handle_first_client_response (DBusAuth         *auth,
    */
   DBusString tmp;
   DBusString tmp2;
-  dbus_bool_t retval;
-  DBusError error;
-  
-  retval = FALSE;
+  dbus_bool_t retval = FALSE;
+  DBusError error = DBUS_ERROR_INIT;
 
   _dbus_string_set_length (&auth->challenge, 0);
   
@@ -578,7 +576,6 @@ sha1_handle_first_client_response (DBusAuth         *auth,
   
   if (auth->keyring == NULL)
     {
-      dbus_error_init (&error);
       auth->keyring = _dbus_keyring_new_for_credentials (auth->desired_identity,
                                                          &auth->context,
                                                          &error);
@@ -610,7 +607,6 @@ sha1_handle_first_client_response (DBusAuth         *auth,
 
   _dbus_assert (auth->keyring != NULL);
 
-  dbus_error_init (&error);
   auth->cookie_id = _dbus_keyring_get_best_key (auth->keyring, &error);
   if (auth->cookie_id < 0)
     {
@@ -640,8 +636,25 @@ sha1_handle_first_client_response (DBusAuth         *auth,
   if (!_dbus_string_append (&tmp2, " "))
     goto out;  
   
-  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES))
-    goto out;
+  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES, &error))
+    {
+      if (dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY))
+        {
+          dbus_error_free (&error);
+          goto out;
+        }
+      else
+        {
+          _DBUS_ASSERT_ERROR_IS_SET (&error);
+          _dbus_verbose ("%s: Error generating challenge: %s\n",
+                         DBUS_AUTH_NAME (auth), error.message);
+          if (send_rejected (auth))
+            retval = TRUE; /* retval is only about mem */
+
+          dbus_error_free (&error);
+          goto out;
+        }
+    }
 
   _dbus_string_set_length (&auth->challenge, 0);
   if (!_dbus_string_hex_encode (&tmp, 0, &auth->challenge, 0))
@@ -826,7 +839,7 @@ handle_client_data_cookie_sha1_mech (DBusAuth         *auth,
    * name, the cookie ID, and the server challenge, separated by
    * spaces. We send back our challenge string and the correct hash.
    */
-  dbus_bool_t retval;
+  dbus_bool_t retval = FALSE;
   DBusString context;
   DBusString cookie_id_str;
   DBusString server_challenge;
@@ -835,9 +848,8 @@ handle_client_data_cookie_sha1_mech (DBusAuth         *auth,
   DBusString tmp;
   int i, j;
   long val;
-  
-  retval = FALSE;                 
-  
+  DBusError error = DBUS_ERROR_INIT;
+
   if (!_dbus_string_find_blank (data, 0, &i))
     {
       if (send_error (auth,
@@ -903,9 +915,6 @@ handle_client_data_cookie_sha1_mech (DBusAuth         *auth,
 
   if (auth->keyring == NULL)
     {
-      DBusError error;
-
-      dbus_error_init (&error);
       auth->keyring = _dbus_keyring_new_for_credentials (NULL,
                                                          &context,
                                                          &error);
@@ -942,9 +951,28 @@ handle_client_data_cookie_sha1_mech (DBusAuth         *auth,
   
   if (!_dbus_string_init (&tmp))
     goto out_3;
-  
-  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES))
-    goto out_4;
+
+  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES, &error))
+    {
+      if (dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY))
+        {
+          dbus_error_free (&error);
+          goto out_4;
+        }
+      else
+        {
+          _DBUS_ASSERT_ERROR_IS_SET (&error);
+
+          _dbus_verbose ("%s: Failed to generate challenge: %s\n",
+                         DBUS_AUTH_NAME (auth), error.message);
+
+          if (send_error (auth, "Failed to generate challenge"))
+            retval = TRUE; /* retval is only about mem */
+
+          dbus_error_free (&error);
+          goto out_4;
+        }
+    }
 
   if (!_dbus_string_init (&client_challenge))
     goto out_4;