thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 163 insertions, 0 deletions

diff --git a/drivers/usb/misc/usb4604.c b/drivers/usb/misc/usb4604.c
new file mode 100644
index 000000000..2ae965671
--- /dev/null
+++ b/drivers/usb/misc/usb4604.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for SMSC USB4604 USB HSIC 4-port 2.0 hub controller driver
+ * Based on usb3503 driver
+ *
+ * Copyright (c) 2012-2013 Dongjin Kim (tobetter@gmail.com)
+ * Copyright (c) 2016 Linaro Ltd.
+ */
+
+#include <linux/i2c.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/gpio/consumer.h>
+
+enum usb4604_mode {
+	USB4604_MODE_UNKNOWN,
+	USB4604_MODE_HUB,
+	USB4604_MODE_STANDBY,
+};
+
+struct usb4604 {
+	enum usb4604_mode	mode;
+	struct device		*dev;
+	struct gpio_desc	*gpio_reset;
+};
+
+static void usb4604_reset(struct usb4604 *hub, int state)
+{
+	gpiod_set_value_cansleep(hub->gpio_reset, state);
+
+	/* Wait for i2c logic to come up */
+	if (state)
+		msleep(250);
+}
+
+static int usb4604_connect(struct usb4604 *hub)
+{
+	struct device *dev = hub->dev;
+	struct i2c_client *client = to_i2c_client(dev);
+	int err;
+	u8 connect_cmd[] = { 0xaa, 0x55, 0x00 };
+
+	usb4604_reset(hub, 1);
+
+	err = i2c_master_send(client, connect_cmd, ARRAY_SIZE(connect_cmd));
+	if (err < 0) {
+		usb4604_reset(hub, 0);
+		return err;
+	}
+
+	hub->mode = USB4604_MODE_HUB;
+	dev_dbg(dev, "switched to HUB mode\n");
+
+	return 0;
+}
+
+static int usb4604_switch_mode(struct usb4604 *hub, enum usb4604_mode mode)
+{
+	struct device *dev = hub->dev;
+	int err = 0;
+
+	switch (mode) {
+	case USB4604_MODE_HUB:
+		err = usb4604_connect(hub);
+		break;
+
+	case USB4604_MODE_STANDBY:
+		usb4604_reset(hub, 0);
+		dev_dbg(dev, "switched to STANDBY mode\n");
+		break;
+
+	default:
+		dev_err(dev, "unknown mode is requested\n");
+		err = -EINVAL;
+		break;
+	}
+
+	return err;
+}
+
+static int usb4604_probe(struct usb4604 *hub)
+{
+	struct device *dev = hub->dev;
+	struct device_node *np = dev->of_node;
+	struct gpio_desc *gpio;
+	u32 mode = USB4604_MODE_HUB;
+
+	gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio))
+		return PTR_ERR(gpio);
+	hub->gpio_reset = gpio;
+
+	if (of_property_read_u32(np, "initial-mode", &hub->mode))
+		hub->mode = mode;
+
+	return usb4604_switch_mode(hub, hub->mode);
+}
+
+static int usb4604_i2c_probe(struct i2c_client *i2c)
+{
+	struct usb4604 *hub;
+
+	hub = devm_kzalloc(&i2c->dev, sizeof(*hub), GFP_KERNEL);
+	if (!hub)
+		return -ENOMEM;
+
+	i2c_set_clientdata(i2c, hub);
+	hub->dev = &i2c->dev;
+
+	return usb4604_probe(hub);
+}
+
+static int __maybe_unused usb4604_i2c_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb4604 *hub = i2c_get_clientdata(client);
+
+	usb4604_switch_mode(hub, USB4604_MODE_STANDBY);
+
+	return 0;
+}
+
+static int __maybe_unused usb4604_i2c_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb4604 *hub = i2c_get_clientdata(client);
+
+	usb4604_switch_mode(hub, hub->mode);
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(usb4604_i2c_pm_ops, usb4604_i2c_suspend,
+		usb4604_i2c_resume);
+
+static const struct i2c_device_id usb4604_id[] = {
+	{ .name = "usb4604" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, usb4604_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id usb4604_of_match[] = {
+	{ .compatible = "smsc,usb4604" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, usb4604_of_match);
+#endif
+
+static struct i2c_driver usb4604_i2c_driver = {
+	.driver = {
+		.name = "usb4604",
+		.pm = pm_ptr(&usb4604_i2c_pm_ops),
+		.of_match_table = of_match_ptr(usb4604_of_match),
+	},
+	.probe		= usb4604_i2c_probe,
+	.id_table	= usb4604_id,
+};
+module_i2c_driver(usb4604_i2c_driver);
+
+MODULE_DESCRIPTION("USB4604 USB HUB driver");
+MODULE_LICENSE("GPL v2");