[PATCH v2 4/4] cdx: use generic driver_override infrastructure

[Runyu Xiao]

CDX devices still keep driver_override in bus-private storage.

The sysfs write side updates that string through driver_set_override(),
which replaces the pointer and frees the old value. However,
driver_match_device() can call cdx_bus_match() from __driver_attach()
without holding the device lock, and cdx_bus_match() still dereferences
that private pointer directly.

That means the CDX match path can race with a concurrent
driver_override update and compare against freed memory.

Switch CDX to the driver-core driver_override infrastructure. This
removes the private driver_override storage, lets the core provide the
sysfs attribute, and uses device_match_driver_override() for the locked
read in cdx_bus_match().

Preserve the existing CDX override_only semantics: entries marked
override_only still require a matching driver_override, but ordinary ID
matches continue to work unchanged.

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@xxxxxxxxxx/
Fixes: 48a6c7bced2a ("cdx: add device attributes")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
---
drivers/cdx/cdx.c           | 40 +++++--------------------------------
include/linux/cdx/cdx_bus.h |  1 -
 2 files changed, 5 insertions(+), 36 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..f1a107b232da 100644
--- a/include/linux/cdx/cdx_bus.h
+++ b/include/linux/cdx/cdx_bus.h
@@ -165,7 +165,6 @@ struct cdx_device {
 	bool enabled;
 	u32 msi_dev_id;
 	u32 num_msi;
-	const char *driver_override;
 	struct mutex irqchip_lock;
 	bool msi_write_pending;
 };
-- 
2.34.1