[PATCH 5.10 224/290] misc: fastrpc: restrict user apps from sending kernel RPC messages

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

From: Dmitry Baryshkov <redacted>

commit 20c40794eb85ea29852d7bc37c55713802a543d6 upstream.

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: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Cc: Srinivas Kandagatla <redacted>
Cc: Jonathan Marek <redacted>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Baryshkov <redacted>
Link: https://lore.kernel.org/r/20210212192658.3476137-1-dmitry.baryshkov@linaro.org (local)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/misc/fastrpc.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c

@@ -948,6 +948,11 @@ static int fastrpc_internal_invoke(struc
 	if (!fl->cctx->rpdev)
 		return -EPIPE;
 
+	if (handle == FASTRPC_INIT_HANDLE && !kernel) {
+		dev_warn_ratelimited(fl->sctx->dev, "user app trying to send a kernel RPC message (%d)\n",  handle);
+		return -EPERM;
+	}
+
 	ctx = fastrpc_context_alloc(fl, kernel, sc, args);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);