Index: modules/comment/comment.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/comment/comment.module,v
retrieving revision 1.615
diff -u -p -r1.615 comment.module
--- modules/comment/comment.module	8 Jan 2008 10:35:41 -0000	1.615
+++ modules/comment/comment.module	10 Jan 2008 15:02:20 -0000
@@ -1652,7 +1652,13 @@ function comment_controls_submit($form, 
   $comments_per_page = $form_state['values']['comments_per_page'];
 
   if ($user->uid) {
-    $user = user_save($user, array('mode' => $mode, 'sort' => $order, 'comments_per_page' => $comments_per_page));
+    $account = user_save($user, array('mode' => $mode, 'sort' => $order, 'comments_per_page' => $comments_per_page));
+    // Terminate if an error occured during user_save().
+    if (!$account) {
+      drupal_set_message(t("Error saving user account."), 'error');
+      return;
+    }
+    $user = $account;
   }
   else {
     $_SESSION['comment_mode'] = $mode;
Index: modules/openid/openid.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/openid/openid.module,v
retrieving revision 1.15
diff -u -p -r1.15 openid.module
--- modules/openid/openid.module	20 Dec 2007 08:57:54 -0000	1.15
+++ modules/openid/openid.module	10 Jan 2008 15:02:21 -0000
@@ -393,6 +393,11 @@ function openid_authentication($response
     else {
       unset($form_state['values']['response']);
       $account = user_save('', $form_state['values']);
+      // Terminate if an error occured during user_save().
+      if (!$account) {
+        drupal_set_message(t("Error saving user account."), 'error');
+        drupal_goto();
+      }
       user_external_login($account);
     }
     drupal_redirect_form($form, $form_state['redirect']);
Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.884
diff -u -p -r1.884 user.module
--- modules/user/user.module	8 Jan 2008 10:35:43 -0000	1.884
+++ modules/user/user.module	10 Jan 2008 15:02:25 -0000
@@ -200,6 +200,9 @@ function user_load($array = array()) {
  *
  * @param $category
  *   (optional) The category for storing profile information in.
+ *
+ * @return
+ *   A fully-loaded $user object upon successful save or FALSE if the save failed.
  */
 function user_save($account, $array = array(), $category = 'account') {
   // Dynamically compose a SQL query:
@@ -238,7 +241,11 @@ function user_save($account, $array = ar
     $query .= "data = '%s' ";
     $v[] = serialize($data);
 
-    db_query("UPDATE {users} SET $query WHERE uid = %d", array_merge($v, array($account->uid)));
+    $success = db_query("UPDATE {users} SET $query WHERE uid = %d", array_merge($v, array($account->uid)));
+    if (!$success) {
+      // The query failed - better to abort the save than risk further data loss.
+      return FALSE;
+    }
 
     // Reload user roles if provided
     if (isset($array['roles']) && is_array($array['roles'])) {
@@ -311,10 +318,15 @@ function user_save($account, $array = ar
           break;
       }
     }
-    db_query('INSERT INTO {users} ('. implode(', ', $fields) .') VALUES ('. implode(', ', $s) .')', $values);
-    $array['uid'] = db_last_insert_id('users', 'uid');
-
+    $success = db_query('INSERT INTO {users} ('. implode(', ', $fields) .') VALUES ('. implode(', ', $s) .')', $values);
+    if (!$success) {
+      // On a failed INSERT some other existing user's uid may be returned.  We
+      // must abort to avoid overwirting their account.
+      return FALSE;
+    }
+    
     // Build the initial user object.
+    $array['uid'] = db_last_insert_id('users', 'uid');
     $user = user_load(array('uid' => $array['uid']));
 
     user_module_invoke('insert', $array, $user, $category);
@@ -1361,7 +1373,13 @@ function user_external_login_register($n
   if (!isset($user->uid)) {
     // Register this new user.
     $userinfo = array('name' => $name, 'pass' => user_password(), 'init' => $name, 'status' => 1, "authname_$module" => $name);
-    $user = user_save('', $userinfo);
+    $account = user_save('', $userinfo);
+    // Terminate if an error occured during user_save().
+    if (!$account) {
+      drupal_set_message(t("Error saving user account."), 'error');
+      return;
+    }
+    $user = $account;
     watchdog('user', 'New external user: %name using module %module.', array('%name' => $name, '%module' => $module), WATCHDOG_NOTICE, l(t('edit'), 'user/'. $user->uid .'/edit'));
   }
 }
@@ -2207,6 +2225,12 @@ function user_register_submit($form, &$f
     $merge_data['status'] = variable_get('user_register', 1) == 1;
   }
   $account = user_save('', array_merge($form_state['values'], $merge_data));
+  // Terminate if an error occured during user_save().
+  if (!$account) {
+    drupal_set_message(t("Error saving user account."), 'error');
+    $form_state['redirect'] = '';
+    return;
+  }
   $form_state['user'] = $account;
 
   watchdog('user', 'New user: %name (%email).', array('%name' => $name, '%email' => $mail), WATCHDOG_NOTICE, l(t('edit'), 'user/'. $account->uid .'/edit'));