fix(xmpp): treat disco#info result without 'from' as from the server

RFC 6120 §8.1.2.1: a stanza received over a c2s stream without a 'from'
attribute must be treated as coming from the server itself. The
on-connect disco#info handler passed the absent attribute as NULL into
connection_features_received(), where g_str_hash() dereferenced the NULL
key and crashed (remotely triggerable DoS on connect).

Substitute connection_get_domain() at both disco#info handler
boundaries, and make connection_features_received() and
connection_get_features() NULL-safe as defense in depth. Add a stabber
regression test answering the on-connect disco#info with a from-less
result.

Fixes #168

src/xmpp/connection.c

@@ -753,7 +753,11 @@ void
 connection_features_received(const char* const jid)
 {
     log_info("[CONNECTION] connection_features_received %s", jid);
-    if (g_hash_table_remove(conn.requested_features, jid) && g_hash_table_size(conn.requested_features) == 0) {
+    const char* key = jid ? jid : conn.domain; // g_str_hash crashes on NULL; NULL 'from' means the server (RFC 6120 §8.1.2.1)
+    if (!key) {
+        return;
+    }
+    if (g_hash_table_remove(conn.requested_features, key) && g_hash_table_size(conn.requested_features) == 0) {
         sv_ev_connection_features_received();
     }
 }
@@ -761,7 +765,11 @@ connection_features_received(const char* const jid)
 GHashTable*
 connection_get_features(const char* const jid)
 {
-    return g_hash_table_lookup(conn.features_by_jid, jid);
+    const char* key = jid ? jid : conn.domain;
+    if (!key || !conn.features_by_jid) {
+        return NULL;
+    }
+    return g_hash_table_lookup(conn.features_by_jid, key);
 }
 
 GList*

src/xmpp/iq.c

@@ -2314,6 +2314,7 @@ _disco_info_response_id_handler(xmpp_stanza_t* const stanza, void* const userdat
         log_debug("Received disco#info response from: %s", from);
     } else {
         log_debug("Received disco#info response");
+        from = connection_get_domain(); // RFC 6120 §8.1.2.1: no 'from' means the server itself
     }
 
     // handle error responses
@@ -2397,6 +2398,7 @@ _disco_info_response_id_handler_onconnect(xmpp_stanza_t* const stanza, void* con
         log_debug("Received disco#info response from: %s", from);
     } else {
         log_debug("Received disco#info response");
+        from = connection_get_domain(); // RFC 6120 §8.1.2.1: no 'from' means the server itself
     }
 
     // handle error responses

tests/functionaltests/functionaltests.c

@@ -173,6 +173,7 @@ main(int argc, char* argv[])
         PROF_FUNC_TEST(disco_info_without_name),
         PROF_FUNC_TEST(disco_items_without_name),
         PROF_FUNC_TEST(disco_info_service_unavailable),
+        PROF_FUNC_TEST(disco_info_result_no_from),
 
         /* Roster management - add/remove/rename contacts */
         PROF_FUNC_TEST(sends_new_item),

tests/functionaltests/test_disco.c

@@ -396,6 +396,35 @@ disco_items_without_name(void **state)
     prof_timeout_reset();
 }
 
+void
+disco_info_result_no_from(void **state)
+{
+    /*
+     * Test that a disco#info result without a 'from' attribute is treated as
+     * coming from the server itself (RFC 6120 §8.1.2.1). The on-connect
+     * disco#info handler used to crash on such responses (issue #168).
+     */
+    stbbr_for_query("http://jabber.org/protocol/disco#info",
+        "<iq to='stabber@localhost/profanity' type='result'>"
+            "<query xmlns='http://jabber.org/protocol/disco#info'>"
+                "<identity category='server' type='im' name='NoFromServer'/>"
+                "<feature var='urn:xmpp:ping'/>"
+            "</query>"
+        "</iq>"
+    );
+
+    /* the on-connect disco#info gets the same from-less response */
+    prof_connect();
+
+    prof_input("/disco info");
+
+    prof_timeout(10);
+    /* client survived and attributed the response to the server */
+    assert_true(prof_output_exact("Service discovery info for localhost"));
+    assert_true(prof_output_regex("NoFromServer.*im.*server"));
+    prof_timeout_reset();
+}
+
 void
 disco_info_service_unavailable(void **state)
 {

tests/functionaltests/test_disco.h

@@ -17,3 +17,4 @@ void disco_info_multiple_identities(void **state);
 void disco_info_without_name(void **state);
 void disco_items_without_name(void **state);
 void disco_info_service_unavailable(void **state);
+void disco_info_result_no_from(void **state);