Update huburi for FeedSub if PuSH signature is invalid

This because some remote server might have used third party PuSH hubs
but switch and we don't know about it.

Possible risks here are of course MITM that could force us to rediscover
PuSH hubs from a feed they control, but that currently feels ... meh.

plugins/OStatus/classes/FeedSub.php

@@ -17,9 +17,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-if (!defined('STATUSNET')) {
-    exit(1);
-}
+if (!defined('GNUSOCIAL')) { exit(1); }
 
 /**
  * @package OStatusPlugin
@@ -41,16 +39,6 @@ PuSH subscription flow:
         hub sends us updates via POST
 
 */
-class FeedDBException extends FeedSubException
-{
-    public $obj;
-
-    function __construct($obj)
-    {
-        parent::__construct('Database insert failure');
-        $this->obj = $obj;
-    }
-}
 
 /**
  * FeedSub handles low-level PubHubSubbub (PuSH) subscriptions.
@@ -220,7 +208,7 @@ class FeedSub extends Managed_DataObject
     public function ensureHub()
     {
         if ($this->sub_state !== 'inactive') {
-            throw new ServerException('Can only ensure WebSub hub for inactive (unsubscribed) feeds.');
+            common_log(LOG_INFO, sprintf('Running hub discovery a possibly active feed in %s state for URI %s', _ve($this->sub_state), _ve($this->uri)));
         }
 
         $discover = new FeedDiscovery();
@@ -235,11 +223,28 @@ class FeedSub extends Managed_DataObject
 
         $orig = !empty($this->id) ? clone($this) : null;
 
+        if (!empty($this->huburi) && $this->huburi !== $huburi) {
+            // There was a huburi already and now we're replacing it,
+            // so we have to set a new secret because otherwise we're
+            // possibly vulnerable to attack from the previous hub.
+
+            // ...but as I understand it this is done in $this->doSubscribe()
+            // which is called from $this->subscribe() (which in turn is
+            // called from $this->renew())
+        }
         $this->huburi = $huburi;
 
         if (!empty($this->id)) {
-            $this->update($orig);
+            $result = $this->update($orig);
+            if ($result === false) {
+                // TODO: Get a DB exception class going...
+                common_debug('Database update failed for FeedSub id=='._ve($this->id).' with new huburi: '._ve($this->huburi));
+                throw new ServerException('Database update failed for FeedSub.');
+            }
+            return $result;
         }
+
+        return null;    // we haven't done anything with the database
     }
 
     /**
@@ -367,6 +372,7 @@ class FeedSub extends Managed_DataObject
 
     public function renew()
     {
+        common_debug('FeedSub is being renewed for uri=='._ve($this->uri).' on huburi=='._ve($this->huburi));
         $this->subscribe();
     }
 
@@ -510,10 +516,25 @@ class FeedSub extends Managed_DataObject
             return;
         }
 
-        if (!$this->validatePushSig($post, $hmac)) {
-            // Per spec we silently drop input with a bad sig,
-            // while reporting receipt to the server.
-            return;
+        try {
+            if (!$this->validatePushSig($post, $hmac)) {
+                // Per spec we silently drop input with a bad sig,
+                // while reporting receipt to the server.
+                return;
+            }
+        } catch (FeedSubBadPushSignatureException $e) {
+            // We got a signature, so something could be wrong. Let's check to see if
+            // maybe upstream has switched to another hub. Let's fetch feed and then
+            // compare rel="hub" with $this->huburi
+
+            $old_huburi = $this->huburi;
+            $this->ensureHub();
+            common_debug(sprintf('Feed uri==%s huburi before=%s after=%s', _ve($this->uri), _ve($old_huburi), _ve($this->huburi)));
+
+            if ($old_huburi !== $this->huburi) {
+                // let's make sure that this new hub knows that we want to subscribe
+                $this->renew();
+            }
         }
 
         $this->receiveFeed($post);
@@ -588,10 +609,12 @@ class FeedSub extends Managed_DataObject
                 }
 
                 $our_hmac = hash_hmac($hash_algo, $post, $this->secret);
-                if ($their_hmac === $our_hmac) {
-                    return true;
+                if ($their_hmac !== $our_hmac) {
+                    common_log(LOG_ERR, sprintf(__METHOD__.': ignoring PuSH with bad HMAC hash: got %s, expected %s for feed %s from hub %s', _ve($their_hmac), _ve($our_hmac), _ve($this->getUri()), _ve($this->huburi)));
+                    throw FeedSubBadPushSignatureException('Incoming PuSH signature did not match expected HMAC hash.');
                 }
-                common_log(LOG_ERR, sprintf(__METHOD__.': ignoring PuSH with bad HMAC hash: got %s, expected %s for feed %s from hub %s', _ve($their_hmac), _ve($our_hmac), _ve($this->getUri()), _ve($this->huburi)));
+                return true;
+
             } else {
                 common_log(LOG_ERR, sprintf(__METHOD__.': ignoring PuSH with bogus HMAC==', _ve($hmac)));
             }

plugins/OStatus/lib/feeddbexception.php

@@ -0,0 +1,12 @@
+<?php
+
+class FeedDBException extends FeedSubException
+{
+    public $obj;
+
+    function __construct($obj)
+    {
+        parent::__construct('Database insert failure');
+        $this->obj = $obj;
+    }
+}

plugins/OStatus/lib/feedsubbadpushsignatureexception.php

@@ -0,0 +1,5 @@
+<?php
+
+class FeedSubBadPushSignatureException extends Exception
+{
+}