media: v4l2-ctrls-api: fix error handling for v4l2_g_ctrl()

As detected by Coverity, the error check logic at get_ctrl() is
broken: if ptr_to_user() fails to fill a control due to an error,
no errors are returned and v4l2_g_ctrl() returns success on a
failed operation, which may cause applications to fail.

Add an error check at get_ctrl() and ensure that it will
be returned to userspace without filling the control value if
get_ctrl() fails.

Fixes: 71c689d ("media: v4l2-ctrls: split up into four source files")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Author: mchehab

drivers/media/v4l2-core/v4l2-ctrls-api.c

@@ -753,9 +753,10 @@ static int get_ctrl(struct v4l2_ctrl *ctrl, struct v4l2_ext_control *c)
 		for (i = 0; i < master->ncontrols; i++)
 			cur_to_new(master->cluster[i]);
 		ret = call_op(master, g_volatile_ctrl);
-		new_to_user(c, ctrl);
+		if (!ret)
+			ret = new_to_user(c, ctrl);
 	} else {
-		cur_to_user(c, ctrl);
+		ret = cur_to_user(c, ctrl);
 	}
 	v4l2_ctrl_unlock(master);
 	return ret;
@@ -770,7 +771,10 @@ int v4l2_g_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *control)
 	if (!ctrl || !ctrl->is_int)
 		return -EINVAL;
 	ret = get_ctrl(ctrl, &c);
-	control->value = c.value;
+
+	if (!ret)
+		control->value = c.value;
+
 	return ret;
 }
 EXPORT_SYMBOL(v4l2_g_ctrl);
@@ -811,10 +815,11 @@ static int set_ctrl_lock(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
 	int ret;
 
 	v4l2_ctrl_lock(ctrl);
-	user_to_new(c, ctrl);
-	ret = set_ctrl(fh, ctrl, 0);
+	ret = user_to_new(c, ctrl);
+	if (!ret)
+		ret = set_ctrl(fh, ctrl, 0);
 	if (!ret)
-		cur_to_user(c, ctrl);
+		ret = cur_to_user(c, ctrl);
 	v4l2_ctrl_unlock(ctrl);
 	return ret;
 }