[Spice-devel] [PATCH spice-server] red-worker: Fix leak processing update commands

[Christophe Fergeau]

On Fri, Sep 01, 2017 at 04:05:25PM +0100, Frediano Ziglio wrote:
> Is possible to have a leak processing update commands if
> the update command is synchronous and the rectangle list
> is empty. Note that Qemu always pass an empty list.
> 
> If the list is empty display_channel_update fill the list.
> This is used to send back the list in case of asynchronous
> requests. But in handle_dev_update_async (the callback that
> handle the asynchronous case) the list is correctly freed.
> 
> This was discovered by accident looking at the code.
> 
> Reproduced with a Windows recording file using GCC address
> sanitizer and this patch to spice-server-replay:
> 
> --- a/server/red-replay-qxl.c
> +++ b/server/red-replay-qxl.c
> @@ -1280,7 +1280,10 @@ static void replay_handle_dev_input(QXLWorker *worker, SpiceReplay *replay,
>          replay->created_primary = FALSE;
>          worker->destroy_surfaces(worker);
>          break;
> -    case RED_WORKER_MESSAGE_UPDATE:
> +    case RED_WORKER_MESSAGE_UPDATE: {
> +        QXLRect update = { 0, 0, 100, 100 };
> +        worker->update_area(worker, 0, &update, NULL, 0, 0);
> +        } break;
>          // XXX do anything? we record the correct bitmaps already.
>      case RED_WORKER_MESSAGE_DISPLAY_CONNECT:
>          // we want to ignore this one - it is sent on client connection, we

NB: inline patches in commit logs confuse git am :-/

> 
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
>  server/red-worker.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/server/red-worker.c b/server/red-worker.c
> index 4d8566be..594dec55 100644
> --- a/server/red-worker.c
> +++ b/server/red-worker.c
> @@ -437,13 +437,17 @@ static void handle_dev_update(void *opaque, void *payload)
>  {
>      RedWorker *worker = opaque;
>      RedWorkerMessageUpdate *msg = payload;
> +    QXLRect *qxl_dirty_rects = msg->qxl_dirty_rects;
>  
>      spice_return_if_fail(worker->running);
>  
>      flush_display_commands(worker);
>      display_channel_update(worker->display_channel,
>                             msg->surface_id, msg->qxl_area, msg->clear_dirty_region,
> -                           &msg->qxl_dirty_rects, &msg->num_dirty_rects);
> +                           &qxl_dirty_rects, &msg->num_dirty_rects);
> +    if (msg->qxl_dirty_rects != qxl_dirty_rects) {
> +        free(qxl_dirty_rects);
> +    }

Given that the caller (red_qxl_update_area) does not care about the
msg->qxl_dirty_rects/msg->num_dirty_rects, I guess you could always pass
NULL, and update display_channel_update accordingly. Maybe it would even
be enough to call display_channel_draw() here instead?

Christophe