Commit e5f34cdd authored by Gerd Hoffmann's avatar Gerd Hoffmann
Browse files

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: default avatarGerd Hoffmann <kraxel@redhat.com>
parent 86fdcf23

ui/vnc.c

+43 −3
Original line number Diff line number Diff line
@@ -68,12 +68,34 @@ static void vnc_set_share_mode(VncState *vs, VncShareMode mode) 
            vs->csock, mn[vs->share_mode], mn[mode]);

#endif



    if (vs->share_mode == VNC_SHARE_MODE_EXCLUSIVE) {

    switch (vs->share_mode) {

    case VNC_SHARE_MODE_CONNECTING:

        vs->vd->num_connecting--;

        break;

    case VNC_SHARE_MODE_SHARED:

        vs->vd->num_shared--;

        break;

    case VNC_SHARE_MODE_EXCLUSIVE:

        vs->vd->num_exclusive--;

        break;

    default:

        break;

    }



    vs->share_mode = mode;

    if (vs->share_mode == VNC_SHARE_MODE_EXCLUSIVE) {



    switch (vs->share_mode) {

    case VNC_SHARE_MODE_CONNECTING:

        vs->vd->num_connecting++;

        break;

    case VNC_SHARE_MODE_SHARED:

        vs->vd->num_shared++;

        break;

    case VNC_SHARE_MODE_EXCLUSIVE:

        vs->vd->num_exclusive++;

        break;

    default:

        break;

    }

}
@@ -2337,6 +2359,11 @@ static int protocol_client_init(VncState *vs, uint8_t *data, size_t len) 
    }

    vnc_set_share_mode(vs, mode);



    if (vs->vd->num_shared > vs->vd->connections_limit) {

        vnc_disconnect_start(vs);

        return 0;

    }



    vs->client_width = pixman_image_get_width(vs->vd->server);

    vs->client_height = pixman_image_get_height(vs->vd->server);

    vnc_write_u16(vs, vs->client_width);
@@ -2889,6 +2916,15 @@ static void vnc_connect(VncDisplay *vd, int csock, 
    {

        vnc_init_state(vs);

    }



    if (vd->num_connecting > vd->connections_limit) {

        QTAILQ_FOREACH(vs, &vd->clients, next) {

            if (vs->share_mode == VNC_SHARE_MODE_CONNECTING) {

                vnc_disconnect_start(vs);

                return;

            }

        }

    }

}



void vnc_init_state(VncState *vs)
@@ -2907,7 +2943,7 @@ void vnc_init_state(VncState *vs) 
    qemu_mutex_init(&vs->output_mutex);

    vs->bh = qemu_bh_new(vnc_jobs_bh, vs);



    QTAILQ_INSERT_HEAD(&vd->clients, vs, next);

    QTAILQ_INSERT_TAIL(&vd->clients, vs, next);



    graphic_hw_update(vd->dcl.con);
@@ -3097,6 +3133,9 @@ static QemuOptsList qemu_vnc_opts = { 
        },{

            .name = "head",

            .type = QEMU_OPT_NUMBER,

        },{

            .name = "connections",

            .type = QEMU_OPT_NUMBER,

        },{

            .name = "password",

            .type = QEMU_OPT_BOOL,
@@ -3211,6 +3250,7 @@ void vnc_display_open(const char *id, Error **errp) 
    } else {

        vs->share_policy = VNC_SHARE_POLICY_ALLOW_EXCLUSIVE;

    }

    vs->connections_limit = qemu_opt_get_number(opts, "connections", 32);



 #ifdef CONFIG_VNC_WS

    websocket = qemu_opt_get(opts, "websocket");

ui/vnc.h

+3 −0
Original line number Diff line number Diff line
@@ -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