Merge lp:~uoms-gregt/lightdm-gtk-greeter/trim-username into lp:lightdm-gtk-greeter

[Greg Trounson]

Ignore whitespace before and after username when authenticating.

Our use case:
Users press the space bar to either power up the computer or bring the monitor out
of sleep. If the computer is already powered on then that keypress propagates to the username
field in lightdm-gtk-greeter, inserting a <space> before they type their username, resulting in a failed login. With proportional fonts this is almost impossible to see at a glance.

Given that whitespace can never be part of a valid username (cf IEEE 1003.1-2001), this patch trims the beginning and end of the username string before passing it to the authentication code. <Space> characters still appear in the username field, but have no effect.

To test:
At a lightdm login prompt, type:
<space>username
or:
username<space>
then enter your password.

Pre-patch:
The login will fail.
Post-patch:
The login will succeed.

Unmerged revisions

477. By Greg Trounson <email address hidden> on 2019-02-10

Ignore whitespace before and after username when authenticating

=== modified file 'src/lightdm-gtk-greeter.c'
--- src/lightdm-gtk-greeter.c	2018-03-15 00:29:41 +0000
+++ src/lightdm-gtk-greeter.c	2019-02-10 20:58:40 +0000
@@ -1999,13 +1999,17 @@
     password_prompted = FALSE;
     prompt_active = FALSE;
 
+    gchar* trimmed_username;
+    trimmed_username = g_strdup (username);
+    g_strstrip (trimmed_username);
+
     if (pending_questions)
     {
         g_slist_free_full (pending_questions, (GDestroyNotify) pam_message_finalize);
         pending_questions = NULL;
     }
 
-    config_set_string (STATE_SECTION_GREETER, STATE_KEY_LAST_USER, username);
+    config_set_string (STATE_SECTION_GREETER, STATE_KEY_LAST_USER, trimmed_username);
 
     if (g_strcmp0 (username, "*other") == 0)
     {
@@ -2031,7 +2035,7 @@
 			}
 		}
     }
-    else if (g_strcmp0 (username, "*guest") == 0)
+    else if (g_strcmp0 (trimmed_username, "*guest") == 0)
     {
 #ifdef HAVE_LIBLIGHTDMGOBJECT_1_19_2
         lightdm_greeter_authenticate_as_guest (greeter, NULL);
@@ -2043,7 +2047,7 @@
     {
         LightDMUser *user;
 
-        user = lightdm_user_list_get_user_by_name (lightdm_user_list_get_instance (), username);
+        user = lightdm_user_list_get_user_by_name (lightdm_user_list_get_instance (), trimmed_username);
         if (user)
         {
             if (!current_session)
@@ -2057,11 +2061,12 @@
             set_language (NULL);
         }
 #ifdef HAVE_LIBLIGHTDMGOBJECT_1_19_2
-        lightdm_greeter_authenticate (greeter, username, NULL);
+        lightdm_greeter_authenticate (greeter, trimmed_username, NULL);
 #else
-        lightdm_greeter_authenticate (greeter, username);
+        lightdm_greeter_authenticate (greeter, trimmed_username);
 #endif
     }
+    g_free (trimmed_username);
 }
 
 static void