patch "serdev: fix registration of second slave" added to tty-testing

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    serdev: fix registration of second slave

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


>From 08fcee289f341786eb3b44e5f2d1dc850943238e Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@xxxxxxxxxx>
Date: Tue, 10 Oct 2017 18:09:49 +0200
Subject: serdev: fix registration of second slave

Serdev currently only supports a single slave device, but the required
sanity checks to prevent further registration attempts were missing.

If a serial-port node has two child nodes with compatible properties,
the OF code would try to register two slave devices using the same id
and name. Driver core will not allow this (and there will be loud
complaints), but the controller's slave pointer would already have been
set to address of the soon to be deallocated second struct
serdev_device. As the first slave device remains registered, this can
lead to later use-after-free issues when the slave callbacks are
accessed.

Note that while the serdev registration helpers are exported, they are
typically only called by serdev core. Any other (out-of-tree) callers
must serialise registration and deregistration themselves.

Fixes: cd6484e1830b ("serdev: Introduce new bus for serial attached devices")
Cc: stable <stable@xxxxxxxxxxxxxxx>	# 4.11
Cc: Rob Herring <robh@xxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serdev/core.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index ec113e39993f..dde2ddc5967d 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -75,21 +75,32 @@ static int serdev_uevent(struct device *dev, struct kobj_uevent_env *env)
  */
 int serdev_device_add(struct serdev_device *serdev)
 {
+	struct serdev_controller *ctrl = serdev->ctrl;
 	struct device *parent = serdev->dev.parent;
 	int err;
 
 	dev_set_name(&serdev->dev, "%s-%d", dev_name(parent), serdev->nr);
 
+	/* Only a single slave device is currently supported. */
+	if (ctrl->serdev) {
+		dev_err(&serdev->dev, "controller busy\n");
+		return -EBUSY;
+	}
+	ctrl->serdev = serdev;
+
 	err = device_add(&serdev->dev);
 	if (err < 0) {
 		dev_err(&serdev->dev, "Can't add %s, status %d\n",
 			dev_name(&serdev->dev), err);
-		goto err_device_add;
+		goto err_clear_serdev;
 	}
 
 	dev_dbg(&serdev->dev, "device %s registered\n", dev_name(&serdev->dev));
 
-err_device_add:
+	return 0;
+
+err_clear_serdev:
+	ctrl->serdev = NULL;
 	return err;
 }
 EXPORT_SYMBOL_GPL(serdev_device_add);
@@ -100,7 +111,10 @@ EXPORT_SYMBOL_GPL(serdev_device_add);
  */
 void serdev_device_remove(struct serdev_device *serdev)
 {
+	struct serdev_controller *ctrl = serdev->ctrl;
+
 	device_unregister(&serdev->dev);
+	ctrl->serdev = NULL;
 }
 EXPORT_SYMBOL_GPL(serdev_device_remove);
 
@@ -311,7 +325,6 @@ struct serdev_device *serdev_device_alloc(struct serdev_controller *ctrl)
 		return NULL;
 
 	serdev->ctrl = ctrl;
-	ctrl->serdev = serdev;
 	device_initialize(&serdev->dev);
 	serdev->dev.parent = &ctrl->dev;
 	serdev->dev.bus = &serdev_bus_type;
-- 
2.14.2