Apply a limit to the number of items we accept into the keyboard queue.

Impact: Without this limit vnc clients can exhaust host memory by
sending keyboard events faster than qemu feeds them to the guest.

Cc: P J P <ppandit@redhat.com>
Cc: Huawei PSIRT <PSIRT@huawei.com>
Reported-by: jiangxin1@huawei.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 ui/input.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/ui/input.c b/ui/input.c
index ed88cda6d6..fb1f404095 100644
--- a/ui/input.c
+++ b/ui/input.c
@@ -41,6 +41,8 @@ static QTAILQ_HEAD(QemuInputEventQueueHead, QemuInputEventQueue) kbd_queue =
     QTAILQ_HEAD_INITIALIZER(kbd_queue);
 static QEMUTimer *kbd_timer;
 static uint32_t kbd_default_delay_ms = 10;
+static uint32_t queue_count;
+static uint32_t queue_limit = 1024;
 
 QemuInputHandlerState *qemu_input_handler_register(DeviceState *dev,
                                                    QemuInputHandler *handler)
@@ -268,6 +270,7 @@ static void qemu_input_queue_process(void *opaque)
             break;
         }
         QTAILQ_REMOVE(queue, item, node);
+        queue_count--;
         g_free(item);
     }
 }
@@ -282,6 +285,7 @@ static void qemu_input_queue_delay(struct QemuInputEventQueueHead *queue,
     item->delay_ms = delay_ms;
     item->timer = timer;
     QTAILQ_INSERT_TAIL(queue, item, node);
+    queue_count++;
 
     if (start_timer) {
         timer_mod(item->timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL)
@@ -298,6 +302,7 @@ static void qemu_input_queue_event(struct QemuInputEventQueueHead *queue,
     item->src = src;
     item->evt = evt;
     QTAILQ_INSERT_TAIL(queue, item, node);
+    queue_count++;
 }
 
 static void qemu_input_queue_sync(struct QemuInputEventQueueHead *queue)
@@ -306,6 +311,7 @@ static void qemu_input_queue_sync(struct QemuInputEventQueueHead *queue)
 
     item->type = QEMU_INPUT_QUEUE_SYNC;
     QTAILQ_INSERT_TAIL(queue, item, node);
+    queue_count++;
 }
 
 void qemu_input_event_send_impl(QemuConsole *src, InputEvent *evt)
@@ -381,7 +387,7 @@ void qemu_input_event_send_key(QemuConsole *src, KeyValue *key, bool down)
         qemu_input_event_send(src, evt);
         qemu_input_event_sync();
         qapi_free_InputEvent(evt);
-    } else {
+    } else if (queue_count < queue_limit) {
         qemu_input_queue_event(&kbd_queue, src, evt);
         qemu_input_queue_sync(&kbd_queue);
     }
@@ -409,8 +415,10 @@ void qemu_input_event_send_key_delay(uint32_t delay_ms)
         kbd_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL, qemu_input_queue_process,
                                  &kbd_queue);
     }
-    qemu_input_queue_delay(&kbd_queue, kbd_timer,
-                           delay_ms ? delay_ms : kbd_default_delay_ms);
+    if (queue_count < queue_limit) {
+        qemu_input_queue_delay(&kbd_queue, kbd_timer,
+                               delay_ms ? delay_ms : kbd_default_delay_ms);
+    }
 }
 
 InputEvent *qemu_input_event_new_btn(InputButton btn, bool down)
-- 
2.9.3

On Fri, Apr 28, 2017 at 10:42:37AM +0200, Gerd Hoffmann wrote:
> Apply a limit to the number of items we accept into the keyboard queue.

Is there a need for similar protection fir mouse input events from VNC ?

> Impact: Without this limit vnc clients can exhaust host memory by
> sending keyboard events faster than qemu feeds them to the guest.

Ability for a remote network client to crash a host by exhausting
memory should be considered a security flaw & have a CVE allocated
for it.

Regards,
Daniel
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On Fr, 2017-04-28 at 09:49 +0100, Daniel P. Berrange wrote:
> On Fri, Apr 28, 2017 at 10:42:37AM +0200, Gerd Hoffmann wrote:
> > Apply a limit to the number of items we accept into the keyboard queue.
> 
> Is there a need for similar protection fir mouse input events from VNC ?

No, there is no delay queue for mouse events.

> > Impact: Without this limit vnc clients can exhaust host memory by
> > sending keyboard events faster than qemu feeds them to the guest.
> 
> Ability for a remote network client to crash a host by exhausting
> memory should be considered a security flaw & have a CVE allocated
> for it.

Sure, it's WIP, Prasit will get one.

cheers,
  Gerd

  Hello Dan,

+-- On Fri, 28 Apr 2017, Daniel P. Berrange wrote --+
| Ability for a remote network client to crash a host by exhausting
| memory should be considered a security flaw & have a CVE allocated
| for it.

Yes, I'm getting it assigned.
--
Prasad J Pandit / Red Hat Product Security Team
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