[PATCH 03/12] cdx: use generic driver_override infrastructure

[Danilo Krummrich <dakr@kernel.org>]

When a driver is probed through __driver_attach(), the bus' match()
callback is called without the device lock held, thus accessing the
driver_override field without a lock, which can cause a UAF.

Fix this by using the driver-core driver_override infrastructure taking
care of proper locking internally.

Note that calling match() from __driver_attach() without the device lock
held is intentional. [1]

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/ [1]
Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
Fixes: 2959ab247061 ("cdx: add the cdx bus driver")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/cdx/cdx.c           | 40 +++++--------------------------------
 include/linux/cdx/cdx_bus.h |  4 ----
 2 files changed, 5 insertions(+), 39 deletions(-)

diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
index 9196dc50a48d..d3d230247262 100644
--- a/drivers/cdx/cdx.c
+++ b/drivers/cdx/cdx.c
@@ -156,8 +156,6 @@ static int cdx_unregister_device(struct device *dev,
 	} else {
 		cdx_destroy_res_attr(cdx_dev, MAX_CDX_DEV_RESOURCES);
 		debugfs_remove_recursive(cdx_dev->debugfs_dir);
-		kfree(cdx_dev->driver_override);
-		cdx_dev->driver_override = NULL;
 	}
 
 	/*
@@ -268,6 +266,7 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 	const struct cdx_driver *cdx_drv = to_cdx_driver(drv);
 	const struct cdx_device_id *found_id = NULL;
 	const struct cdx_device_id *ids;
+	int ret;
 
 	if (cdx_dev->is_bus)
 		return false;
@@ -275,7 +274,8 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 	ids = cdx_drv->match_id_table;
 
 	/* When driver_override is set, only bind to the matching driver */
-	if (cdx_dev->driver_override && strcmp(cdx_dev->driver_override, drv->name))
+	ret = device_match_driver_override(dev, drv);
+	if (ret == 0)
 		return false;
 
 	found_id = cdx_match_id(ids, cdx_dev);
@@ -289,7 +289,7 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 		 */
 		if (!found_id->override_only)
 			return true;
-		if (cdx_dev->driver_override)
+		if (ret > 0)
 			return true;
 
 		ids = found_id + 1;
@@ -453,36 +453,6 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(modalias);
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct cdx_device *cdx_dev = to_cdx_device(dev);
-	int ret;
-
-	if (WARN_ON(dev->bus != &cdx_bus_type))
-		return -EINVAL;
-
-	ret = driver_set_override(dev, &cdx_dev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct cdx_device *cdx_dev = to_cdx_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", cdx_dev->driver_override);
-	device_unlock(dev);
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 static ssize_t enable_store(struct device *dev, struct device_attribute *attr,
 			    const char *buf, size_t count)
 {
@@ -552,7 +522,6 @@ static struct attribute *cdx_dev_attrs[] = {
 	&dev_attr_class.attr,
 	&dev_attr_revision.attr,
 	&dev_attr_modalias.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -646,6 +615,7 @@ ATTRIBUTE_GROUPS(cdx_bus);
 
 const struct bus_type cdx_bus_type = {
 	.name		= "cdx",
+	.driver_override = true,
 	.match		= cdx_bus_match,
 	.probe		= cdx_probe,
 	.remove		= cdx_remove,
diff --git a/include/linux/cdx/cdx_bus.h b/include/linux/cdx/cdx_bus.h
index b1ba97f6c9ad..f54770f110bc 100644
--- a/include/linux/cdx/cdx_bus.h
+++ b/include/linux/cdx/cdx_bus.h
@@ -137,9 +137,6 @@ struct cdx_controller {
  * @enabled: is this bus enabled
  * @msi_dev_id: MSI Device ID associated with CDX device
  * @num_msi: Number of MSI's supported by the device
- * @driver_override: driver name to force a match; do not set directly,
- *                   because core frees it; use driver_set_override() to
- *                   set or clear it.
  * @irqchip_lock: lock to synchronize irq/msi configuration
  * @msi_write_pending: MSI write pending for this device
  */
@@ -165,7 +162,6 @@ struct cdx_device {
 	bool enabled;
 	u32 msi_dev_id;
 	u32 num_msi;
-	const char *driver_override;
 	struct mutex irqchip_lock;
 	bool msi_write_pending;
 };
-- 
2.53.0