From ecf6457cdbc76f1430dc47c394a0ef5e4c28a80f Mon Sep 17 00:00:00 2001
From: Dmitry Podgorny <pasis.ua@gmail.com>
Date: Sun, 21 Mar 2021 16:34:49 +0200
Subject: [PATCH] conn: send stream attribute "from" after TLS negotiation

RFC6120 states that client SHOULD send the "from" attribute in <stream>.

Because of privacy concerns attribute "from" should be sent only after
TLS negotiation. This step ensures that the server is verified by its
certificate and protects JID from MITM attack.

Fixes #163.
Also should be helpful for #162.
---
 src/conn.c | 65 +++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 20 deletions(-)

diff --git a/src/conn.c b/src/conn.c
index 1cdeb96..d3bc8d8 100644
--- a/src/conn.c
+++ b/src/conn.c
@@ -52,6 +52,9 @@ static int _disconnect_cleanup(xmpp_conn_t *conn, void *userdata);
 static char *_conn_build_stream_tag(xmpp_conn_t *conn,
                                     char **attributes,
                                     size_t attributes_len);
+static int _conn_open_stream_with_attributes(xmpp_conn_t *conn,
+                                             char **attributes,
+                                             size_t attributes_len);
 static void _conn_attributes_new(xmpp_conn_t *conn,
                                  char **attrs,
                                  char ***attributes,
@@ -656,20 +659,12 @@ int xmpp_conn_open_stream(xmpp_conn_t *conn,
                           char **attributes,
                           size_t attributes_len)
 {
-    char *tag;
-
     if (!conn->is_raw)
         return XMPP_EINVOP;
 
-    tag = _conn_build_stream_tag(conn, attributes, attributes_len);
-    if (!tag)
-        return XMPP_EMEM;
-
     conn_prepare_reset(conn, auth_handle_open_raw);
-    xmpp_send_raw_string(conn, "<?xml version=\"1.0\"?>%s", tag);
-    xmpp_free(conn->ctx, tag);
 
-    return XMPP_EOK;
+    return _conn_open_stream_with_attributes(conn, attributes, attributes_len);
 }
 
 /** Start synchronous TLS handshake with the server.
@@ -884,17 +879,31 @@ void xmpp_send(xmpp_conn_t *conn, xmpp_stanza_t *stanza)
  */
 void conn_open_stream(xmpp_conn_t *conn)
 {
-    xmpp_send_raw_string(conn,
-                         "<?xml version=\"1.0\"?>"
-                         "<stream:stream to=\"%s\" "
-                         "xml:lang=\"%s\" "
-                         "version=\"1.0\" "
-                         "xmlns=\"%s\" "
-                         "xmlns:stream=\"%s\">",
-                         conn->domain, conn->lang,
-                         conn->type == XMPP_CLIENT ? XMPP_NS_CLIENT
-                                                   : XMPP_NS_COMPONENT,
-                         XMPP_NS_STREAMS);
+    size_t attributes_len;
+    int rc;
+    char *from = NULL;
+    char *ns = conn->type == XMPP_CLIENT ? XMPP_NS_CLIENT : XMPP_NS_COMPONENT;
+    char *attributes[12] = {
+        "to",           conn->domain,    "xml:lang", conn->lang,
+        "version",      "1.0",           "xmlns",    ns,
+        "xmlns:stream", XMPP_NS_STREAMS, "from",     NULL};
+
+    attributes_len = ARRAY_SIZE(attributes);
+    if (conn->tls && conn->jid && strchr(conn->jid, '@') != NULL)
+        from = xmpp_jid_bare(conn->ctx, conn->jid);
+
+    if (from)
+        attributes[attributes_len - 1] = from;
+    else
+        attributes_len -= 2;
+
+    rc = _conn_open_stream_with_attributes(conn, attributes, attributes_len);
+    if (rc != XMPP_EOK) {
+        xmpp_error(conn->ctx, "conn", "Cannot build stream tag: memory error");
+        conn_disconnect(conn);
+    }
+    if (from)
+        xmpp_free(conn->ctx, from);
 }
 
 int conn_tls_start(xmpp_conn_t *conn)
@@ -1113,6 +1122,22 @@ static char *_conn_build_stream_tag(xmpp_conn_t *conn,
     return tag;
 }
 
+static int _conn_open_stream_with_attributes(xmpp_conn_t *conn,
+                                             char **attributes,
+                                             size_t attributes_len)
+{
+    char *tag;
+
+    tag = _conn_build_stream_tag(conn, attributes, attributes_len);
+    if (!tag)
+        return XMPP_EMEM;
+
+    xmpp_send_raw_string(conn, "<?xml version=\"1.0\"?>%s", tag);
+    xmpp_free(conn->ctx, tag);
+
+    return XMPP_EOK;
+}
+
 static void _conn_attributes_new(xmpp_conn_t *conn,
                                  char **attrs,
                                  char ***attributes,