[PATCH v2 3/5] Drivers: hv: vmbus: 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]

Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
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: d765edbb301c ("vmbus: add driver_override support")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/hv/vmbus_drv.c | 43 ++++++++++--------------------------------
 include/linux/hyperv.h |  5 -----
 2 files changed, 10 insertions(+), 38 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index d28ff45d4cfd..acfb579828c5 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -538,34 +538,6 @@ static ssize_t device_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(device);
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct hv_device *hv_dev = device_to_hv_device(dev);
-	int ret;
-
-	ret = driver_set_override(dev, &hv_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 hv_device *hv_dev = device_to_hv_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", hv_dev->driver_override);
-	device_unlock(dev);
-
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 /* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
 static struct attribute *vmbus_dev_attrs[] = {
 	&dev_attr_id.attr,
@@ -596,7 +568,6 @@ static struct attribute *vmbus_dev_attrs[] = {
 	&dev_attr_channel_vp_mapping.attr,
 	&dev_attr_vendor.attr,
 	&dev_attr_device.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -708,9 +679,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
 {
 	const guid_t *guid = &dev->dev_type;
 	const struct hv_vmbus_device_id *id;
+	int ret;
 
-	/* When driver_override is set, only bind to the matching driver */
-	if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+	/* If a driver override is set, only bind to the matching driver */
+	ret = device_match_driver_override(&dev->device, &drv->driver);
+	if (ret == 0)
 		return NULL;
 
 	/* Look at the dynamic ids first, before the static ones */
@@ -718,8 +691,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
 	if (!id)
 		id = hv_vmbus_dev_match(drv->id_table, guid);
 
-	/* driver_override will always match, send a dummy id */
-	if (!id && dev->driver_override)
+	/*
+	 * If there's a matching driver override, this function should succeed,
+	 * thus return a dummy device ID if no matching ID is found.
+	 */
+	if (!id && ret > 0)
 		id = &vmbus_device_null;
 
 	return id;
@@ -1021,6 +997,7 @@ static const struct dev_pm_ops vmbus_pm = {
 /* The one and only one */
 static const struct bus_type  hv_bus = {
 	.name =		"vmbus",
+	.driver_override =	true,
 	.match =		vmbus_match,
 	.shutdown =		vmbus_shutdown,
 	.remove =		vmbus_remove,
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 964f1be8150c..c054d7eff622 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1272,11 +1272,6 @@ struct hv_device {
 	u16 device_id;
 
 	struct device device;
-	/*
-	 * Driver name to force a match.  Do not set directly, because core
-	 * frees it.  Use driver_set_override() to set or clear it.
-	 */
-	const char *driver_override;
 
 	struct vmbus_channel *channel;
 	struct kset	     *channels_kset;
-- 
2.54.0