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vnc: track & limit connections

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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>
This commit is contained in:
Gerd Hoffmann 2014-10-02 12:09:34 +02:00
parent 86fdcf23f4
commit e5f34cdd2d
2 changed files with 46 additions and 3 deletions
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46
ui/vnc.c
View File

@ -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");

3
ui/vnc.h
View File

@ -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