Verify that user applications are not using the kernel RPC message
handle to restrict them from directly attaching to guest OS on the
remote subsystem. This is a port of CVE-2019-2308 fix.

Fixes: c68cfb71 ("misc: fastrpc: Add support for context Invoke method")
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Jonathan Marek <jonathan@marek.ca>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210212192658.3476137-1-dmitry.baryshkov@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>