[char-misc V4.5] mei: validate request value in client notify request ioctl

[Tomas Winkler <tomas.winkler@intel.com>]

From: Alexander Usyskin <alexander.usyskin@intel.com>

This patch address a possible security issue:

The request field in client notify request ioctl comes from user space
as u32 and is downcasted to u8 with out validation.
Check request field to have approved values
MEI_HBM_NOTIFICATION_STAR/STOP

Cc: <stable@vger.kernel.org> #4.3+
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
---
 drivers/misc/mei/main.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/mei/main.c b/drivers/misc/mei/main.c
index 677d0362f334..80f9afcb1382 100644
--- a/drivers/misc/mei/main.c
+++ b/drivers/misc/mei/main.c
@@ -458,7 +458,11 @@ static int mei_ioctl_client_notify_request(struct file *file, u32 request)
 {
 	struct mei_cl *cl = file->private_data;
 
-	return mei_cl_notify_request(cl, file, request);
+	if (request != MEI_HBM_NOTIFICATION_START &&
+	    request != MEI_HBM_NOTIFICATION_STOP)
+		return -EINVAL;
+
+	return mei_cl_notify_request(cl, file, (u8)request);
 }
 
 /**
-- 
2.4.3