ui: introduce "password-secret" option for VNC servers

Currently when using VNC the "password" flag turns on password based
authentication. The actual password has to be provided separately via
the monitor.

This introduces a "password-secret" option which lets the password be
provided up front.

  $QEMU --object secret,id=vncsec0,file=passwd.txt \
        --vnc localhost:0,password-secret=vncsec0

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210311114343.439820-2-berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

qemu-options.hx

@@ -2165,6 +2165,11 @@ SRST
         time to allow <protocol> password to expire immediately or never
         expire.
 
+    ``password-secret=<secret-id>``
+        Require that password based authentication is used for client
+        connections, using the password provided by the ``secret``
+        object identified by ``secret-id``.
+
     ``tls-creds=ID``
         Provides the ID of a set of TLS credentials to use to secure the
         VNC server. They will apply to both the normal VNC server socket

ui/vnc.c

@@ -48,6 +48,7 @@
 #include "crypto/tlscredsanon.h"
 #include "crypto/tlscredsx509.h"
 #include "crypto/random.h"
+#include "crypto/secret_common.h"
 #include "qom/object_interfaces.h"
 #include "qemu/cutils.h"
 #include "qemu/help_option.h"
@@ -3459,6 +3460,9 @@ static QemuOptsList qemu_vnc_opts = {
         },{
             .name = "password",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "password-secret",
+            .type = QEMU_OPT_STRING,
         },{
             .name = "reverse",
             .type = QEMU_OPT_BOOL,
@@ -3931,6 +3935,7 @@ void vnc_display_open(const char *id, Error **errp)
     int lock_key_sync = 1;
     int key_delay_ms;
     const char *audiodev;
+    const char *passwordSecret;
 
     if (!vd) {
         error_setg(errp, "VNC display not active");
@@ -3948,7 +3953,23 @@ void vnc_display_open(const char *id, Error **errp)
         goto fail;
     }
 
-    password = qemu_opt_get_bool(opts, "password", false);
+
+    passwordSecret = qemu_opt_get(opts, "password-secret");
+    if (passwordSecret) {
+        if (qemu_opt_get(opts, "password")) {
+            error_setg(errp,
+                       "'password' flag is redundant with 'password-secret'");
+            goto fail;
+        }
+        vd->password = qcrypto_secret_lookup_as_utf8(passwordSecret,
+                                                     errp);
+        if (!vd->password) {
+            goto fail;
+        }
+        password = true;
+    } else {
+        password = qemu_opt_get_bool(opts, "password", false);
+    }
     if (password) {
         if (fips_get_state()) {
             error_setg(errp,