[Qemu-devel] [PULL 6/9] ui: fix setup of VNC websockets auth scheme with TLS

[Gerd Hoffmann <kraxel@redhat.com>]

From: "Daniel P. Berrange" <berrange@redhat.com>

The way the websockets TLS code was integrated into the VNC server
made it essentially useless. The only time that the websockets TLS
support could be used is if the primary VNC server had its existing
TLS support disabled. ie QEMU had to be launched with:

  # qemu -vnc localhost:1,websockets=5902,x509=/path/to/certs

Note the absence of the 'tls' flag. This is already a bug, because
the docs indicate that 'x509' is ignored unless 'tls' is given.

If the primary VNC server had TLS turned on via the 'tls' flag,
then this prevented the websockets TLS support from being used,
because it activates the VeNCrypt auth which would have resulted
in TLS being run over a TLS session. Of course no websockets VNC
client supported VeNCrypt so in practice, since the browser clients
cannot setup a nested TLS session over the main HTTPS connection,
so it would not even get past auth.

This patch causes us to decide our auth scheme separately for the
main VNC server vs the websockets VNC server. We take account of
the fact that if TLS is enabled, then the websockets client will
use https, so setting up VeNCrypt is thus redundant as it would
lead to nested TLS sessions.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 ui/vnc.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
 ui/vnc.h |  2 ++
 2 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/ui/vnc.c b/ui/vnc.c
index 8edbb67..7b66f93 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -3012,9 +3012,16 @@ static void vnc_connect(VncDisplay *vd, int csock,
 	vs->auth = VNC_AUTH_NONE;
 	vs->subauth = VNC_AUTH_INVALID;
     } else {
-	vs->auth = vd->auth;
-	vs->subauth = vd->subauth;
+        if (websocket) {
+            vs->auth = vd->ws_auth;
+            vs->subauth = VNC_AUTH_INVALID;
+        } else {
+            vs->auth = vd->auth;
+            vs->subauth = vd->subauth;
+        }
     }
+    VNC_DEBUG("Client sock=%d ws=%d auth=%d subauth=%d\n",
+              csock, websocket, vs->auth, vs->subauth);
 
     vs->lossy_rect = g_malloc0(VNC_STAT_ROWS * sizeof (*vs->lossy_rect));
     for (i = 0; i < VNC_STAT_ROWS; ++i) {
@@ -3028,7 +3035,7 @@ static void vnc_connect(VncDisplay *vd, int csock,
     if (websocket) {
         vs->websocket = 1;
 #ifdef CONFIG_VNC_TLS
-        if (vd->tls.x509cert) {
+        if (vd->ws_tls) {
             qemu_set_fd_handler2(vs->csock, NULL, vncws_tls_handshake_peek,
                                  NULL, vs);
         } else
@@ -3320,7 +3327,8 @@ vnc_display_setup_auth(VncDisplay *vs,
                        bool password,
                        bool sasl,
                        bool tls,
-                       bool x509)
+                       bool x509,
+                       bool websocket)
 {
     /*
      * We have a choice of 3 authentication options
@@ -3355,10 +3363,26 @@ vnc_display_setup_auth(VncDisplay *vs,
      * in an appropriate manner. In regular VNC, all the
      * TLS options get mapped into VNC_AUTH_VENCRYPT
      * sub-auth types.
+     *
+     * In websockets, the https:// protocol already provides
+     * TLS support, so there is no need to make use of the
+     * VeNCrypt extension. Furthermore, websockets browser
+     * clients could not use VeNCrypt even if they wanted to,
+     * as they cannot control when the TLS handshake takes
+     * place. Thus there is no option but to rely on https://,
+     * meaning combinations 4->6 and 7->9 will be mapped to
+     * VNC auth schemes in the same way as combos 1->3.
+     *
+     * Regardless of fact that we have a different mapping to
+     * VNC auth mechs for plain VNC vs websockets VNC, the end
+     * result has the same security characteristics.
      */
     if (password) {
         if (tls) {
             vs->auth = VNC_AUTH_VENCRYPT;
+            if (websocket) {
+                vs->ws_tls = true;
+            }
             if (x509) {
                 VNC_DEBUG("Initializing VNC server with x509 password auth\n");
                 vs->subauth = VNC_AUTH_VENCRYPT_X509VNC;
@@ -3371,9 +3395,17 @@ vnc_display_setup_auth(VncDisplay *vs,
             vs->auth = VNC_AUTH_VNC;
             vs->subauth = VNC_AUTH_INVALID;
         }
+        if (websocket) {
+            vs->ws_auth = VNC_AUTH_VNC;
+        } else {
+            vs->ws_auth = VNC_AUTH_INVALID;
+        }
     } else if (sasl) {
         if (tls) {
             vs->auth = VNC_AUTH_VENCRYPT;
+            if (websocket) {
+                vs->ws_tls = true;
+            }
             if (x509) {
                 VNC_DEBUG("Initializing VNC server with x509 SASL auth\n");
                 vs->subauth = VNC_AUTH_VENCRYPT_X509SASL;
@@ -3386,9 +3418,17 @@ vnc_display_setup_auth(VncDisplay *vs,
             vs->auth = VNC_AUTH_SASL;
             vs->subauth = VNC_AUTH_INVALID;
         }
+        if (websocket) {
+            vs->ws_auth = VNC_AUTH_SASL;
+        } else {
+            vs->ws_auth = VNC_AUTH_INVALID;
+        }
     } else {
         if (tls) {
             vs->auth = VNC_AUTH_VENCRYPT;
+            if (websocket) {
+                vs->ws_tls = true;
+            }
             if (x509) {
                 VNC_DEBUG("Initializing VNC server with x509 no auth\n");
                 vs->subauth = VNC_AUTH_VENCRYPT_X509NONE;
@@ -3401,6 +3441,11 @@ vnc_display_setup_auth(VncDisplay *vs,
             vs->auth = VNC_AUTH_NONE;
             vs->subauth = VNC_AUTH_INVALID;
         }
+        if (websocket) {
+            vs->ws_auth = VNC_AUTH_NONE;
+        } else {
+            vs->ws_auth = VNC_AUTH_INVALID;
+        }
     }
 }
 
@@ -3596,7 +3641,7 @@ void vnc_display_open(const char *id, Error **errp)
     }
 #endif
 
-    vnc_display_setup_auth(vs, password, sasl, tls, x509);
+    vnc_display_setup_auth(vs, password, sasl, tls, x509, websocket);
 
 #ifdef CONFIG_VNC_SASL
     if ((saslErr = sasl_server_init(NULL, "qemu")) != SASL_OK) {
diff --git a/ui/vnc.h b/ui/vnc.h
index 90b2592..aac9156 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -181,6 +181,8 @@ struct VncDisplay
     time_t expires;
     int auth;
     int subauth; /* Used by VeNCrypt */
+    int ws_auth; /* Used by websockets */
+    bool ws_tls; /* Used by websockets */
     bool lossy;
     bool non_adaptive;
 #ifdef CONFIG_VNC_TLS
-- 
1.8.3.1