vnc: track & limit connections

Also track the number of connections in "connecting" and "shared" state
(in addition to the "exclusive" state).  Apply a configurable limit to
these connections.

The logic to apply the limit to connections in "shared" state is pretty
simple:  When the limit is reached no new connections are allowed.

The logic to apply the limit to connections in "connecting" state (this
is the state you are in *before* successful authentication) is
slightly different:  A new connect kicks out the oldest client which is
still in "connecting" state.  This avoids a easy DoS by unauthenticated
users by simply opening connections until the limit is reached.

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/ui/vnc.h b/ui/vnc.h
index 6fe8278126..5e2b1a561e 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -150,7 +150,10 @@ typedef enum VncSharePolicy {
 struct VncDisplay
 {
     QTAILQ_HEAD(, VncState) clients;
+    int num_connecting;
+    int num_shared;
     int num_exclusive;
+    int connections_limit;
     VncSharePolicy share_policy;
     int lsock;
 #ifdef CONFIG_VNC_WS