[Spice-devel] [PATCH spice v2] reds: Cancel unexpected xfer messages

[Frediano Ziglio]

> 
> Inform client that transfer will not work, instead of only
> dropping the agent messages.
> 
> The file transfer messages can be disabled using qemu cli option:
>  "disable-agent-file-xfer"
> 
> Resolves:
> https://bugzilla.redhat.com/show_bug.cgi?id=1373725
> 
> Signed-off-by: Pavel Grunt <pgrunt at redhat.com>
> ---
>  server/reds.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/server/reds.c b/server/reds.c
> index bafd04bab..fd163250d 100644
> --- a/server/reds.c
> +++ b/server/reds.c
> @@ -1111,6 +1111,39 @@ static void
> reds_on_main_agent_monitors_config(RedsState *reds,
>      reds_client_monitors_config_cleanup(reds);
>  }
>  
> +static void agent_data_free(uint8_t *data, G_GNUC_UNUSED void *opaque)
> +{
> +    free(data);
> +}
> +
> +/*
> + * Inform client about discarded file transfer
> + * https://bugzilla.redhat.com/show_bug.cgi?id=1373725
> + */
> +static void agent_xfer_error(MainChannelClient *mcc, const VDAgentMessage
> *message)
> +{
> +    VDAgentMessage *xfer_msg;
> +    VDAgentFileXferStatusMessage *xfer_status;
> +    size_t len;
> +
> +    if (message->type < VD_AGENT_FILE_XFER_START || message->type >
> VD_AGENT_FILE_XFER_DATA) {
> +        return;
> +    }
> +
> +    len = sizeof(VDAgentMessage) + sizeof(VDAgentFileXferStatusMessage);
> +    xfer_msg = spice_malloc0(len);
> +    xfer_msg->protocol = VD_AGENT_PROTOCOL;
> +    xfer_msg->type = VD_AGENT_FILE_XFER_STATUS;
> +    xfer_msg->size = sizeof(VDAgentFileXferStatusMessage);
> +    xfer_status = (VDAgentFileXferStatusMessage *) xfer_msg->data;
> +    xfer_status->id = ((VDAgentFileXferStartMessage *) message->data)->id;

VDAgentFileXferStartMessage should be const but the real problem is this:

reds.c: In function 'agent_xfer_error':
reds.c:1139:5: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
     xfer_status->id = ((VDAgentFileXferStartMessage *) message->data)->id;
     ^~~~~~~~~~~

no idea... but if I write (message+1) instead of message->data (which is from ABI the same)
the warning disappears :-( Not counting that data is uint8_t, a type that is supposed to
be ok to be aliases... but maybe I didn't understand something about aliasing.
Also spice_malloc0 is marked as __attribute__((malloc)) which should tell compiler
that xfer_msg (and so xfer_status) cannot alias...

> +    xfer_status->result = VD_AGENT_FILE_XFER_STATUS_ERROR;
> +
> +    spice_debug("canceling file transfer %u", xfer_status->id);
> +
> +    main_channel_client_push_agent_data(mcc, (uint8_t *) xfer_msg, len,
> agent_data_free, NULL);
> +}
> +
>  void reds_on_main_agent_data(RedsState *reds, MainChannelClient *mcc, const
>  void *message,
>                               size_t size)
>  {
> @@ -1124,6 +1157,7 @@ void reds_on_main_agent_data(RedsState *reds,
> MainChannelClient *mcc, const void
>      case AGENT_MSG_FILTER_OK:
>          break;
>      case AGENT_MSG_FILTER_DISCARD:
> +        agent_xfer_error(mcc, message);
>          return;
>      case AGENT_MSG_FILTER_MONITORS_CONFIG:
>          reds_on_main_agent_monitors_config(reds, mcc, message, size);

Frediano