[Spice-devel] [PATCH] channel: do not free rcc->stream in red_channel_client_disconnect

[Victor Toso]

Hi,

On Tue, Jan 19, 2016 at 09:52:24AM +0000, Frediano Ziglio wrote:
> This fixes a crash if red_channel_client disconnect is called
> handling a message.
> This can happen for instance handling SPICE_MSGC_ACK which calls
> red_channel_client_push which try to write items to socket detecting
> writing errors (for instance socket disconnection).
> Messages are read in a loop and the red_channel_client_disconnect
> would cause rcc->stream to be NULL which will turn in a use-after-free
> problem (stream in red_peer_handle_incoming will use cached stream value).
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau at gmail.com>
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
>  server/red-channel.c | 38 ++++++++++++++++++++++----------------
>  1 file changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/server/red-channel.c b/server/red-channel.c
> index 306c87d..51e8958 100644
> --- a/server/red-channel.c
> +++ b/server/red-channel.c
> @@ -1231,22 +1231,28 @@ void red_channel_client_ref(RedChannelClient *rcc)
>  
>  void red_channel_client_unref(RedChannelClient *rcc)
>  {
> -    if (!--rcc->refs) {
> -        spice_debug("destroy rcc=%p", rcc);
> -        if (rcc->send_data.main.marshaller) {
> -            spice_marshaller_destroy(rcc->send_data.main.marshaller);
> -        }
> +    if (--rcc->refs != 0) {

My opnion is that doing --(var) on if() does not make the code easy
readable. rcc->refs will always be decreased so it should be outside
the conditional.

I see this in multiple places in spice-server but my vote is to change
that at least for new code :)

best,
  toso

> +        return;
> +    }
>  
> -        if (rcc->send_data.urgent.marshaller) {
> -            spice_marshaller_destroy(rcc->send_data.urgent.marshaller);
> -        }
> +    spice_debug("destroy rcc=%p", rcc);
>  
> -        red_channel_client_destroy_remote_caps(rcc);
> -        if (rcc->channel) {
> -            red_channel_unref(rcc->channel);
> -        }
> -        free(rcc);
> +    reds_stream_free(rcc->stream);
> +    rcc->stream = NULL;
> +
> +    if (rcc->send_data.main.marshaller) {
> +        spice_marshaller_destroy(rcc->send_data.main.marshaller);
>      }
> +
> +    if (rcc->send_data.urgent.marshaller) {
> +        spice_marshaller_destroy(rcc->send_data.urgent.marshaller);
> +    }
> +
> +    red_channel_client_destroy_remote_caps(rcc);
> +    if (rcc->channel) {
> +        red_channel_unref(rcc->channel);
> +    }
> +    free(rcc);
>  }
>  
>  void red_channel_client_destroy(RedChannelClient *rcc)
> @@ -1749,7 +1755,7 @@ void red_channel_pipes_add_empty_msg(RedChannel *channel, int msg_type)
>  int red_channel_client_is_connected(RedChannelClient *rcc)
>  {
>      if (!rcc->dummy) {
> -        return rcc->stream != NULL;
> +        return ring_item_is_linked(&rcc->channel_link);
>      } else {
>          return rcc->dummy_connected;
>      }
> @@ -1804,6 +1810,8 @@ static void red_channel_remove_client(RedChannelClient *rcc)
>                        rcc->channel->type, rcc->channel->id,
>                        rcc->channel->thread_id, pthread_self());
>      }
> +    spice_return_if_fail(ring_item_is_linked(&rcc->channel_link));
> +
>      ring_remove(&rcc->channel_link);
>      spice_assert(rcc->channel->clients_num > 0);
>      rcc->channel->clients_num--;
> @@ -1845,8 +1853,6 @@ void red_channel_client_disconnect(RedChannelClient *rcc)
>          rcc->channel->core->watch_remove(rcc->stream->watch);
>          rcc->stream->watch = NULL;
>      }
> -    reds_stream_free(rcc->stream);
> -    rcc->stream = NULL;
>      if (rcc->latency_monitor.timer) {
>          rcc->channel->core->timer_remove(rcc->latency_monitor.timer);
>          rcc->latency_monitor.timer = NULL;
> -- 
> 2.4.3
> 
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